Horus Heresy

"And in that time the Great Beasts shall walk the earth, beneath their tread shall cities become as dust by their burning breath shall civilisations be as ash, So the End of Days is begun."

- The Apocrypha Terra

The Horus Heresy was a galaxy-spanning civil war that consumed the worlds of Mankind for 7 Terran years. Its outbreak marked the end of the Emperor of Mankind's Great Crusade to reunite the scattered colony worlds of humanity under a single government and the beginning of the current Age of the Imperium. The Horus Heresy is in many ways the founding event of the Imperium of Man as it now exists. The conflict was fought across the Milky Way Galaxy in the early centuries of the 31st Millennium and resulted in more than 2.3 trillion dead, 4.6 trillion if one includes the planetary populations purged by the Imperium after the Heresy due to the taint of Chaotic corruption. The Heresy concluded with the death of the traitorous Warmaster Horus, the internment of the Emperor in the Golden Throne and the creation of the Chaos Space Marine Traitor Legions. The Heresy was directly responsible for the birth of the present-day structure of the Space Marine Chapters following the Second Founding and the Reformation of the Imperium by the Ultramarines' Primarch Roboute Guilliman.

Unity
During the turbulent era known as the Age of Strife, the Sol System and the nearby star systems that had been colonised by humanity during the Dark Age of Technology were effectively cut off from interstellar travel or communication with each other. This was due to the massive Warp Storms that swept the galaxy as the Immaterium was roiled by the millennia-long gestation of the Chaos God Slaanesh and the turbulence that marked the decay of the Eldar empire before the Fall. During this dark time, Terra sometimes held sway over the Sol System, while at other times the rulers of Mars or Luna were dominant. The different worlds found themselves constantly at war. During this 5,000 standard-year-long period of anarchy, fear and violence, Old Earth's once unified planetary government had completely broken down and been divided into dozens of warring states of so-called techno-barbarians.

Continuous warfare raged across the surface of Terra for 2,500 years, beginning in the late 27th Millennium. Little remained of the once sophisticated civilisation of Old Earth's glorious past as the centre of a growing human interstellar commonwealth marked by advanced science, high culture and wondrous technologies. Techno-barbarian warlords and their warrior hordes continuously fought over the planet, which had become little more than a massive battleground for their wars of attrition. They made use of chemical, biological and even thermonuclear weapons of mass destruction, and slowly transformed the cradle of Mankind into a battered, post-apocalyptic wasteland across most of its scarred surface. This was a dark period for the people of Old Earth, when they were dominated by brutal rulers and despotic tyrants. It was against this backdrop of oppression, violence and casual brutality that the Emperor of Mankind first revealed Himself openly to the people of Terra. In secret, he had been planning for this moment in history for millennia, ever since the Age of Strife had fractured what remained of the ancient human federation. With his massive army of genetically-enhanced warriors who comprised the first units of the Imperial Army and would serve as the prototypes for the later development of the Space Marines, the Emperor began his conquest of Terra. His intent was to reunite the warring nations of the world into a unified planetary government and then use Terra as the springboard from which to begin his reconquest of the galaxy under the aegis of an Imperium of Man dedicated to the Imperial Truth of progress and reason. Brutal rulers such as the warlord Kalagann of Ursh, Cardinal Tang of the Yndonesic Bloc, and the most infamous of all, the half-mad, half-genius Nathaniel Dume, the Tyrant of the Pan-Pacific Empire, would all fall by the wayside. Once unleashed, the geentically-enhanced armies of the Emperor swept all before them like wheat before the harvester's scythe until all the techno-barbarian warlords had either been conquered outright or had agreed through diplomacy to become subservient to the Emperor's will.

During this time the Emperor created a number of military organisations, such as the Imperial Army, which would become the nucleus of the armed forces that would later support his Space Marine Legions and his reconquest of the human-settled galaxy. Amongst the early Imperial Army units that saw action during the Unification Wars were such venerable regiments as the Geno Five-Two Chiliad, which would become one of the oldest and most respected regiments within the Imperial Army. Like many of these early regiments, the geno-soldiers were created through the use of some of the Emperor's sophisticated genetic engineering techniques, developed in his laboratories beneath the Himalazian (Himalayan) Mountains and by the advanced geneticists who called Luna home. The most elite of this first generation of genetically-engineered supersoldiers were known as the Thunder Warriors, men who were physically stronger and more formidable in combat than even the later Space Marines, though they were engineered to be vicious killers and lacked many of the more noble aspects of the Astartes as well as their tremendously long lifespans. The Thunder Warriors were engineered to be the means to an end and were never intended to be integrated into the Emperor's new realm after Unity had been achieved. Through genetic engineering and selection the standard geno-soldiers displayed many of the characteristics of the perfect human warrior -- they were physically more resilient, stronger and capable of taking more damage than any of their unaltered techno-barbarian foes. These early genetically-engineered Imperial Army regiments would go on to continue serving the Emperor after the conclusion of the Unification Wars. These regiments would eventually be referred to as the Old Hundred, and would form the core of the initial military force that embarked upon the Emperor's galaxy-spanning Great Crusade in the late 30th Millennium beside his newly created Space Marine Legions, the early versions of which had taken part in the later campaigns of the Wars of Unification.

When the Unification Wars were complete around the year 800.M30, the Emperor forged a new unified planetary government for Terra under his leadership. He next journeyed to Mars and met with the Adepts of the Cult Mechanicus. In return for the use of the Mechanicum's vast manufactorums, the use of its Titan Legions and the orbital shipyards to construct the weaponry and starships he would need for the Great Crusade to reunite Mankind under the banner of the Imperial Truth, the Emperor agreed to grant the newborn Adeptus Mechanicus complete autonomy on Mars and its other Forge Worlds as well as an exemption to the atheism required by the Imperial Truth. This agreement, known as the Treaty of Mars (the Treaty of Olympus to the Mechanicus), marks the true foundation of the Imperium of Man in the alliance between Terra and Mars.

Council of War
Following the successful conclusion of the Unification Wars in circa 800.M30, the Emperor convened the ruling body known as the War Council to manage the execution of the Great Crusade intended to reunite the entire human-settled galaxy under a single government. The War Council effectively became the true ruling body of the Imperium during the early and middle years of the Great Crusade. The Emperor Himself sat at the head of the Council; at his left hand was Malcador the Sigillite, perhaps the Emperor's greatest ally during the Wars of Unity and a human psyker whose powers were matched only by those of the Emperor. The rest of the Council was composed of talented administrators drawn from the great ruling aristocratic dynasties of Terra and the Segmentum Solar, and when the Emperor forged his alliance with the Mechanicum of Mars in the Treaty of Mars, the Fabricator-General of the Mechanicum also claimed his seat. The War Council was also attended by the Paternova of the Navigator Houses. As the Emperor departed the homeworld of Mankind to lead the Great Crusade into the stars, he left the legendary Malcador to act as the Regent of Terra and the head of the War Council in his stead. At the same time, Malcador took the lead in creating the clades of Imperial Assassins that would eventually evolve into the Officio Assassinorum, making Malcador the first Grand Master of Assassins.

Great Crusade
When the great Warp Storms that had cut off Terra since the end of the Dark Age of Technology subsided, and the Age of Strife came to an end at the dawn of the 31st Millennium, the Emperor of Mankind deemed it time to begin his Great Crusade, a massive campaign to conquer the galaxy by which he and his armies would free all human-settled colony worlds from alien oppression or primitive ignorance and reunite the human race across the galaxy under the single banner of the new Imperium of Man. To execute this plan, the Emperor created the Primarchs, his god-like, genetically-engineered superhuman offspring. The Primarchs were still in their infancy, growing to hyper-accelerated maturity in their special gestation tanks, when they were snatched away from the genetic laboratory deep beneath the Himalazian (Himalayan) Mountains on Terra where they had been created and gestated by the Emperor using His own DNA. The cause of this disappearance was the Chaos Gods, who were fearful that with the Primarchs, the Emperor would be able to impose Order across the galaxy and weaken their own firm grip on the collective unconsciousness of the minds of men. Uniting their powers, the Dark Gods opened a portal from the Warp and broke into the laboratory through the potent psychic wards the Emperor had erected. Unable to destroy the Primarchs outright because of the protections the Emperor had laid upon them, the Chaos Gods instead chose to scatter them across the galaxy through the Warp. The superhuman infants eventually came to rest on diverse, human-inhabited worlds. It was at this time that the Ruinous Powers first touched the souls of those Primarchs who would eventually turn to the worship of Chaos, infecting them with a shard of corruption. Certainly the fact that each of the Primarchs was ultimately cast ashore on an inhabited human world was no accident; the Chaos Gods may have hoped that by having the Primarchs raised among men without the guidance of the Emperor they would display more of the human weaknesses that would make them easier to corrupt when the time came.

During the Great Crusade, the Emperor encountered each of the Primarchs on their scattered homeworlds in turn. To fill the gap in his military plans for the Great Crusade wrought by the Primarchs' absence, the Emperor had instead Founded 20 Space Marine Legions, several of which had been raised even as the Unifications Wars still raged. The Emperor used the Primarchs' genetic material still in his possession to craft the genetically-enhanced warriors of each Legion. After the Emperor rediscovered his sons scattered across the galaxy, He deemed it fitting that each Primarch should lead their genetic offspring as the commander of the Legion whose Astartes bore their DNA. However, this would prove a critical mistake, as the Space Marine gene-seed creation process made the Emperor, the Primarchs and the Space Marines analogous to Grandfather, Fathers and Sons, respectively, in their genetic inheritance and superhuman abilities. In time, many of the Space Marines in the Legions, especially those recruited from their Primarchs' homeworld rather than from Terra before the Primarchs' rediscovery, would come to venerate and feel more loyalty for their Primarch than the Emperor of Mankind.

Triumph of Ullanor
"You are like a son and together we have all but conquered the galaxy. Now the time has come for me to retire to Terra. My work as a soldier is done and now passes to you for I have great tasks to perform in my earthly sanctum. I name you Warmaster and from this day forth all of my armies and generals shall take orders from you as if the words cam from mine own mouth. But words of caution I have for you for your brother Primarchs are strong of will, of though and of action. Do not seek to change them, but use their particular strengths well. You have much work to do for there are still many words to liberate, many peoples to rescue. My trust is with you. Hail Horus! Hail the Warmaster!"

- The Emperor of Mankind, at the Triumph of Ullanor

The Ullanor Crusade was a vast Imperial assault on the Ork empire of the Overlord Urrlak Urruk during the late 30th Millennium. This massive undertaking would mark the culmination of the Great Crusade's expansion.

Ullanor, the capital world of this empire, and the site of the final assault, lay in the Ullanor System of the galaxy's Ullanor Sector. The Crusade included the deployment of 100,000 Space Marines, 8,000,000 Imperial Army troops, and thousands of Imperial starships and their support personnel. The Ullanor Crusade marked the high point of the Great Crusade's vast effort to reunite the scattered colony worlds of humanity. The Orks of Ullanor represented the largest concentration of Orks ever defeated by the military forces of the Imperium of Man before the Third War for Armageddon began during the late 41st Millennium.

With the great victory sealed in blood and iron, the call to a Triumph was sounded, to recognise this highpoint of the Great Crusade and to honour all the warriors of the Ullanor Crusade, mortals and Astartes alike, for their extraordinary valour and service to humanity's cause. By the Emperor’s command, Ullanor was remade as a trophy world, designated Mundus Tropaeum on all galactic maps and records of tithe. It would be a site of glory and spectacle to cement not only this single conquest over the forces ranged against Mankind, but a greater symbol of the Great Crusade itself. For two hundred Terran years, the Emperor’s mighty endeavour had moved across the face of the galaxy to bring unity and illumination to the lost daughter-worlds of Old Earth. It had pushed back the night, reforged old links between civilisations, battled alien threats -- and with regret, it had often punished those who refused to return to the Imperial fold. A change was coming, though, a change that found its fulcrum on Ullanor. None who walked upon that world knew that the echo of that Triumph would sound for decades, for centuries, for millennia. The glory of this triumphant spectacle as so many of the Imperium's scattered military forces gathered in one place for the first time in centuries was to remain in the mind of every Astartes as the high-point of the great endeavour that they were engaged upon. It would prove to be a bright memory to recall in the dark days of the Horus Heresy after Astartes had turned against Astartes and Primarch against Primarch.

To prepare the world for the Imperial Triumph, geoformer platoons from the Adeptus Mechanicus brought world engines and mobile stone-burners to cut a massive swath across the broken landscape left in the battle’s wake. Orkish dead were buried by the millions with their savage ruins, interred beneath transplanted rocks and the heads of crushed mountains. The Mechanicus eradicated every last remaining trace of the enemy and paved over them with a giant boulevard, a parade stage as wide as the footprint of some entire Imperial cities. They built a highway and allowed only one structure to stand besides the great platform -- an ornamental pavilion of black marble and heavy granite that had been built piecemeal on Terra and then shipped across the void by special envoy. Marker posts decorated with the skulls of Ork commanders paced out the length of the road, and behind them great bowls of smokeless Promethium burned brightly, endlessly lighting the highway with their blue-white fire.

When the Mechanicus had finished their work, the honoured came to pay homage to the battle won, the Great Crusade’s ideal of human unity and the Emperor who was father to all Mankind. The Imperial Army and the Titan Legions bracketed the gathering. Human troops were ranked in uncountable numbers, their host so wide they became a sea of battle armour and dress uniforms. Every common man and woman who stood on Ullanor’s soil that day had been selected for their valour and conduct, and until the day they died each would have the singular honour of wearing the onyx-and-gold Ullanor Triumph Bar upon their uniforms. The award was forged from Bolter shells recovered from the field and melted down. Ranged around them, the great war machines of the Collegia Titanica towered towards a sky cut to ribbons by the contrails of a thousand aerospace fighters; and above those, high over the thin white cirrus clouds of Ullanor’s day, Imperial warships moved as slow as they dared through the upper atmosphere, washes of interface heat rolling off their Void Shields as they showed their flanks in a gesture of renewed fealty.

A full fourteen of the Space Marine Legions stood represented at the Ullanor Triumph, and with them came nine beings of superhuman power and majesty. Nine gods and angels made flesh, the Primarchs of the greatest armies ever created by human hands. Mortarion, the reaper of men and master of the Death Guard, cowled and lethal in aspect, matched by the warrior-guardians of his Deathshroud honour guard. The Phoenician, Fulgrim, resplendent in his finery and handsome in aspect, lit by the reflection of gold and platinum. Magnus the Red, the Crimson King, the lord of the unknown, his soul as much a mystery to the common world as the workings of the Warp and the ghosts within it. Lorgar Aurelian, the quiet and brooding zealot who burned with such intensity and buried it all deep in his heart, saying little and standing watchful. His polar opposite was Angron, the gladiator-lord and son of grief, never able to settle or moderate his seething, endless fury, always on the verge of outburst and violence. Rogal Dorn, the stalwart man of stone, the Imperial Fist with his unswerving manner and unbreakable focus, the one who would always obey, would always be ready for duty. Jaghatai Khan, his fur-trimmed robes and ornate armour detailed with a thousand narratives of the White Scars Legion, his every step across the land a challenge to the galaxy. Then Sanguinius of the Blood Angels, flanked by the gold-armoured honour detail of the Sanguinary Guard, his mighty wings folded back across his battle-plate, his face turned to the sky to welcome the impossible, majestic sight before him. Then, finally, came Horus of the Luna Wolves, the Hero of Ullanor, liberator and first among equals. Horus, who was to be given the new honour of an Imperial title above and beyond any that had been bestowed before; a title, it could be said, that would forever carry the echo of his name. After declaring Horus as Imperial Warmaster and the new supreme commander of the Great Crusade, the Emperor to the shock of those assembled announced his own intention to return to Terra to pursue a secret project intended to benefit all Mankind.

Seeds of Heresy Sown
After more than 200 standard years of hard conflict by the early 31st Millennium, over two million human-settled worlds across the Milky Way Galaxy had been reclaimed by the Emperor in the name of the Imperium of Man. Beside him had stood the Primarch Horus, who had fought alongside the Emperor for the early part of the Great Crusade as his only rediscovered son and primary military commander, glorying in the singular attentions of his father. The long wars had forged a strong bond between them, and they were truly father and son. But now the Emperor had to consolidate his newborn Imperium, and undertake the next phase of his Grand Plan. He intended to create a Webway through the Immaterium much like that used by the Eldar that would be open to humanity by wielding the psychic augmentation technology of the artefact from the Dark Age of Technology known as the Golden Throne. This work required his continued presence on Terra, and so after Horus' magnificent victory in the Ullanor Crusade, against the largest horde of Orks ever encountered in the galaxy at that time, the Emperor departed and left Horus in charge of the Great Crusade with the exclusive title of "Warmaster." As Warmaster, Horus was the commanding general of all of the Imperium of Man's military forces, charged with leading the other Primarchs and their Legions through the remainder of the Great Crusade.

At this announcement there was much shock and outrage. Many of the other Primarchs did not understand why the Emperor was leaving them to fight the enemies of Mankind alone and, worse still, why Horus should be raised as the first amongst equals. Rogal Dorn, Sanguinius and Fulgrim were pleased for their brother, the new Warmaster, while others -- such as Angron, Roboute Guilliman, Lion El'Jonson and Perturabo -- all reacted with varying degrees of disapproval. The situation only grew worse when the Emperor announced that he would be creating a civilian administrative bureaucracy known as the Council of Terra that was comprised of Imperial bureaucrats and nobles to carry out the day-to-day governmental affairs of the Imperium, replacing the direct rule of the Emperor while he was engaged in his secret Imperial Webway Project. The Council of Terra would implement and administer the new galaxy-wide tax of resources and manpower called the Imperial Tithe and other matters of day-to-day law in the Imperium of Man while the Emperor focused on bringing his Webway Project to fruition using the technology of the Golden Throne. The Primarchs would be relegated to a primarily military role as the Imperium's most preeminent commanders. Many of the Primarchs, including Horus, were deeply disturbed that their father would make them subject to normal men and women who had never shed blood in the establishment or expansion of the Imperium and that he would remove them from the political positions of rule to which they believed they were entitled. The Emperor had sought to create a civilian bureaucracy for the Imperium precisely because he wanted regular human beings to learn to govern themselves once more and not become beholden to a permanent, genetically-enhanced ruling class. The Chaos Gods would ultimately use the Primarchs' resentment as one of the all-too-human weaknesses they could exploit to corrupt half their number.

Lords of the Imperium
After the decisive victory during the Ullanor Crusade, when Mankind's re-ascension to predominance in the galaxy was no longer in doubt, the Emperor bestowed upon the Primarch Horus Lupercal the title of Imperial Warmaster and ceded to him control of all the Imperium's military forces in the Emperor's stead. The other Primarchs were then instructed to follow Horus and obey him and complete the Great Crusade under his direction. There was, it is said, some disquiet among the Primarchs that the Emperor had decided to no longer fight alongside them, but the Emperor was as adamant as He was close-mouthed as to what He would do on his return to Terra. The Emperor then departed for the homeworld of Mankind and the dungeons deep beneath his great Imperial Palace to begin His great work on the creation of a human extension into the Eldar Webway under a veil of secrecy previously unknown in the Imperium. He drew to him certain advisors and retired to the private vaults deep beneath his city-fortress within the Imperial Palace.

Upon his return to Terra, the Emperor called to his side Malcador and the Fabricator-General of the Mechanicum. He issued them with new commands. No longer were they to support the military campaigns, as these were now safely in the hands of his sons the Primarchs and the newly appointed Warmaster Horus. The Emperor needed time and all of his focus to be directed at his next great project, which would tie the newborn Imperium together and unite it as no other human polity had ever been united. To this end, the Emperor convened the first Council of Terra. Unlike the War Council, of which Horus was now the leader, the Council of Terra would attend to matters of state and the establishment and maintenance of Imperial Law across the myriad worlds of the Imperium. In particular, the Council of Terra was to administrate the establishment of the Imperial Tithe of troops and resources from all the worlds of the Imperium that were required to support the Great Crusade. In effect, to the new Council of Terra would fall the entirety of the civil government of the Imperium. Malcador, the Emperor's most trusted advisor, was named as the First Lord of the Council and would lead it in the Emperor's absence. The Fabricator-General of the Mechanicum of Mars, Kelbor-Hal, Captain-General Constantin Valdor of the Legio Custodes and the Masters of the Adeptus Astronomica, the Adeptus Astra Telepathica and the Administratum of the Imperium were also appointed to the Council.

Having established the new governing body of the Imperium to carry out the day-to-day work of ruling tens of thousands of worlds and trillions of human beings, the Emperor took refuge in His vast laboratories and workshops beneath the Imperial Palace. He began work in earnest on his new project. While the Emperor was locked away in His subterranean factories, trouble was brewing. The formation of the Council proved to be a contentious decision with the distant Primarchs, who were appalled when news of the formation of the Council of Terra finally reached them on the frontiers of the Great Crusade. Some of the Primarchs took great exception to being ruled by those they deemed less worthy of such an honour than themselves. The less stable Primarchs felt that this was a betrayal of all they had fought and won in the Emperor's name and that their victories now counted for nothing. The Primarchs, and many of their Astartes, felt that it was they who had suffered and sacrificed the most to build the Imperium and thus it was they who should have the greatest say in how it was ruled, not a council composed of effete Terran nobles and faceless bureaucrats. This was one of many growing resentments that allowed the Ruinous Powers to infect and corrupt several of the Primarchs.

The creation of the Council of Terra, seen in this light, lent new weight to Horus' argument to several of his brothers that the Imperium had been betrayed by their father. He argued that the Emperor had proved more than willing to turn His back on his sons and generals and give power instead to petty mortal administrators and the sycophantic Tech-adepts of Mars who lacked the Primarchs' brilliance and superhuman abilities. As Horus prepared his rebellion against the Emperor, he convinced himself that petty functionaries and administrators had supplanted the Primarchs and the Astartes within the Imperium they had won. Once the Imperium had been wholly geared for the war and conquest that was its life's blood since its inception, but now Horus believed that it had become burdened with parasitic exectors, scribes and scriveners who demanded to know the cost of everything. Bureaucracy was taking over -- red tape, administrators and clerks were replacing the heroes of the age. Horus argued to his more receptive brothers that unless the Imperium changed its ways and direction, its greatness as an empire would soon be a footnote in history books. Horus feared that everything he and his brother Primarchs had achieved would be a distant memory of former glory, lost in the mists of time like the civilisations of ancient Terra. It was this hubris and arrogance that led to the Warmaster's inevitable fall to Chaos and the resultant civil war that would consume the entire galaxy, ushering in a new Age of Darkness that would last for millennia.

Yet Horus and his more resentful brothers had completely misunderstood the Emperor's intent in creating the Council of Terra. The Council was to become the body of civilian government that would administrate the myriad bureaucratic tasks needed for the survival of the newly formed human interstellar empire. The Emperor was determined that in His Imperium power would reside with those men and women who were governed by its apparatus and not with an artificial military elite composed of genetically-engineered beings who were so powerful that they already possessed only a very tenuous grip upon their own humanity. The Primarchs and their Space Marines had been created to give life to the Emperor's dream of a united human Imperium stretching across the galaxy and to defend it from humanity's myriad foes. They were not to rule it as a hereditary caste of immortal warriors imposing their whims upon those they deemed mere "mortals" by brute force.

Corruption of the Space Marine Legions
Long before the tragic events that would unfold on Istvaan III and initiate the conflict of the Horus Heresy, the Primarch Lorgar of the Word Bearers Legion had already committed himself and his Astartes to the service of the Ruinous Powers. Lorgar was a puritanical religious zaelot who was said to have experienced visions that foresaw the coming of the Emperor, who he believed to be a living God. This belief resulted in a series of bitter religious wars as Lorgar fought to impose his new religious doctrine worshipping the Emperor on his homeworld of Colchis. When the Emperor finally arrived to reclaim his lost son, the entire world was already enthralled to Lorgar and his Cult of the Emperor. The people of Colchis united behind their new living God. The elaborate celebrations and displays of piety lasted for months, although it was said that the Emperor did not approve of this, wishing to rejoin the Great Crusade as soon as possible and being greatly dismissive of organised religion in general. The Emperor had not begun the Great Crusade to reshackle humanity within the chains of superstition and ignorance but to spread the light of reason and science. At the conclusion of the celebrations, Lorgar was made commander of the XVII Space Marine Legion, the Imperial Heralds, who were renamed the Word Bearers after they embraced their Primarch and his religious beliefs. Kor Phaeron, Lorgar's adoptive father and religious advisor, survived the augmentation process to join the Word Bearers as a rare adult Space Marine, though he would never be a true Astartes. Kor Phaeron became Lorgar's chief adviser, lieutenant and the commander of the Word Bearers' elite 1st Company as the XVII Legion's First Captain.

Lorgar led his Legion throughout the Great Crusade, as the Word Bearers sought to eliminate all blasphemy and heresy within the new Imperium of Man. Ancient texts and icons of other faiths were burned. The construction of vast monuments and cathedrals venerating the Emperor as the God of Mankind were supervised by Lorgar and the Word Bearers on many of the worlds they brought into Imperial Compliance. The greatest Chaplains of the Word Bearers produced enormous works on the divinity and righteousness of the Emperor, and gave grand speeches and sermons to the masses of conquered worlds. The progress of the Word Bearers was slow in bringing new worlds into Imperial Compliance, but the Imperial domination of those who were defeated by the XVII Legion was always complete, as religion proved to be a potent tool in securing Imperial loyalty. At some point during this period, Lorgar penned the work known as the Lectitio Divinitatus, which laid out the case that the Emperor of Mankind was a divine being and was worthy of worship as the rightful God of humanity. This book would later, ironically considering the identity of its author, become instrumental in the founding of the Imperial Cult and the Ecclesiarchy.

Castigation of Khur
At this time, some 40 standard years before the start of the Horus Heresy, the absolute loyalty of Lorgar and the Word Bearers Legion to the Emperor and his Imperium was unquestioned. Their Compliant worlds regularly delivered tithes in the Emperor’s name, and the orders of Terra were accepted without question throughout the worlds liberated by the Word Bearers. Lorgar and his Legion had successfully prosecuted the Emperor's Great Crusade for almost a full Terran century, and in that time the Emperor had never once admonished His zealous son or the Word Bearers Legion for their fervent worship of Him even though such doctrine clashed with the Emperor's Imperial Truth.

But the Emperor, for all His love for His son, was deeply disturbed by Lorgar's unwillingness to embrace reason or alter his practices despite decades of exposure to the advanced science and technology of the Imperium. He had initially tolerated the beliefs of his deeply religious son, but as the Great Crusade reached its height, the Emperor found Himself increasingly frustrated with the slow pace with which Lorgar conquered and then brought worlds into Compliance for the Imperium. The Emperor finally ordered the Word Bearers to cease their religious activities, as their mission was to reunify the galaxy under the banner of the secular Imperial Truth, not preach the word of the Emperor's personal divinity. The Emperor had long opposed the spread of organised religion and was determined to use the creation of the new Imperium of Man to enshrine reason and science, not religion, as the true guiding light of a new interstellar human civilisation. The Emperor was particularly troubled by any notion that He should be worshipped as a God and the actions of the Word Bearers Legion in slaughtering those who refused to accept the Emperor's divinity stank of the religious excesses that had so often poisoned human history.

The Emperor ordered a task force composed of the Ultramarines Legion and lead by their Primarch Roboute Guilliman and accompanied by a force of his elite personal bodyguards, the Legio Custodes and the Imperial Regent, Malcador the Sigillite, to raze the capital city of the planet Khur, a world dear to the Word Bearers, who considered its capital, Monarchia, the "perfect city" because of the intense religious devotion of its citizens and the sheer number of cathedrals and monuments dedicated to the worship of the Emperor as a God. Following the city's destruction by the Ultramarines, the entire Word Bearers Legion, 100,000 Space Marines strong, were ordered to assemble on the planet's surface, within sight of the smoldering ruins of Monarchia, where its Astartes were humiliated and rebuked by the Emperor Himself, who psychically forced everyone, including Lorgar, to kneel before Him, and explained to them that they had failed both Him and humanity. Lorgar was stunned by his father's reproach and refusal to accept his worship, and fell into a deep melancholy.

Feeling betrayed by the Emperor, Lorgar refused audience to all but Kor Phaeron, the Word Bearers' First Captain and Cardinal of its faith. Kor Phaeron was Lorgar's adoptive father and had raised him from infancy on Colchis as a member of the Colchisiam religious order called the Covenant. Kor Phaeron had served as Lorgar's chief lieutenant and advisor since the time when he ruled as the theocrat of Colchis. Lorgar also called the the Legion's First Chaplain Erebus to his side, who had long been another trusted advisor. Kor Phaeron and Erebus sympathised with Lorgar's unrequited religious longings, and felt that the Word Bearers Legion should serve gods truly worthy of their worship. Kor Phaeron and Erebus explained that they knew of such gods, the divine beings once worshipped by the Old Faith of Colchis. Thus, it was in this way that Lorgar first learned of the existence of the Chaos Gods, who not only accepted the zealous worship he offered, but demanded it. Thus the seeds of the Horus Heresy were first sown amongst the Word Bearers. Intrigued, Lorgar demanded that the Legion find these gods, and Kor Phaeron and Erebus, both of whom had been secret devotees of Chaos for decades, proposed a pilgrimage.

Pilgrimage of Lorgar
Prompted by First Captain Kor Phaeron and the XVII Legion's First Chaplain Erebus, both secret devotees of the Chaos Gods through Colchis' Old Faith, Lorgar journeyed with his Word Bearers Legion's Chapter of the Serrated Sun to what was then the fringes of known Imperial space as part of the 1301st Expeditionary Fleet of the Great Crusade. At this time, Lorgar had not yet fallen to the corruption of Chaos, though he had turned against the Emperor of Mankind as a deity no longer worthy of his worship. Lorgar believed that the Emperor was wrong to condemn Mankind's natural instinct to seek out the divine as an unworthy superstition and he intended to discover if there were truly deities worthy of humanity's respect. To this end, though Lorgar no longer had any love or loyalty for the Emperor, he and his XVII Legion rejoined the Great Crusade but did so only so their efforts could serve as a front for their pursuit of the Pilgrimage of Lorgar.

The Word Bearers were also accompanied on this Pilgrimage by 5 members of the Legio Custodes who had been set by the Emperor to watch over everything the Word Bearers did to prevent them from falling back into error once more. The Word Bearers' pursuit of any scrap of information that could be found on the Primordial Truth or the nature of the place where Gods and mortals could mingle ultimately led the 1301st Expeditionary Fleet to the Cadia System near the largest permanent Warp Storm in the galaxy, later known to the Imperium as the Eye of Terror. The Expeditionary Fleet's Master of Astropaths advised Lorgar that unusual "voices" in the Warp were heard in the vicinity of the great Warp rift, voices that spoke directly to the Primarch as well, which were the voices of the Chaos entities within the Immaterium. It would be in the Cadia System that Lorgar would learn that his suspicions had been correct and that the shape of all of the religions across the galaxy that possessed so many similarities to the Colchisian Old Faith were not artefacts of Mankind's collective unconsciousness, but expressions of worship in the universal truth that was Chaos.

Primordial Truth
The so-called "Primordial Truth" of the existence of Chaos changed Lorgar and the Word Bearers forever as they were exposed to the Ruinous Powers and slowly corrupted, the first of the Space Marine Legions to worship the Chaos Gods and become Traitors to the Emperor in their hearts. Lorgar and the Word Bearers spent the remaining years of the Great Crusade attempting to enlighten humanity about the true spiritual nature of Creation, ultimately resorting to manipulation and deception to sway nine of the Primarchs to the cause of Chaos as their Gods demanded, the most notable being the Warmaster Horus. When it became clear that Mankind could not be enlightened by Chaos without first being forcibly weaned at a great price in blood from the Emperor's false Imperial Truth, Lorgar would go on to willingly help orchestrate the terrible Battle of Istvaan III and the Drop Site Massacre at Istvaan V as well as the larger Horus Heresy itself. When Horus openly declared his rebellion against the Emperor, the Word Bearers were one of the first Legions to support him and his cause. The worlds they had conquered since their conversion to Chaos also joined the side of the Traitors, having been secretly corrupted to the worship of the Ruinous Powers in the final days of the Great Crusade.

Fall of Horus
During the Great Crusade, it became apparent that the Primarchs were far from the perfect specimens of humanity they were intended to be. Although each Primarch was physically and mentally god-like compared to a baseline human being, they harboured the flaws of vanity, egotism, hunger for power, jealousy, arrogance, insecurity and all the other sins of the human character.

As the Warmaster, Horus took over command of the Great Crusade, and accepted his new duties with earnest dedication. However, there was much dissension in the ranks of the Primarchs and other parties in the Imperium over the Emperor's decision to withdraw from the campaign and return to Terra as well as to reorganise the administration of the Imperium. Only a handful of the Primarchs, among them a scheming Lorgar, remained steadfast beside the Warmaster during this period of conflict. Horus also disagreed with many of the decrees passed by the newly established Council of Terra, intended to shift the burden of taxation and administration onto the newly-conquered ("Imperial Compliant") worlds. Even worse, Horus came to believe in his heart that he was failing his father, and was deeply wounded that the Emperor had revealed to none of the Primarchs, not even his most favoured son, why he had secluded himself upon Terra and the truth behind his secret Webway Project. These seeds of bitterness, resentment and frustration grew, and would soon bear deadly fruit.

It was on the moon of the world of Davin that Horus' fate was sealed. This was the second time his Legion had been posted to this world; after the previous visit sixty years earlier the Luna Wolves had adopted the native Davinite institution of warrior lodges. Though these lodges had begun as simple fraternities of warriors, their secretive nature handed Lorgar, the Primarch of the Word Bearers Legion and his First Chaplain Erebus, the tool they needed to manipulate Horus towards the service of the Chaos Gods.

Lorgar and his Word Bearers originally came from Colchis, a world defined by religious fanaticism, and had long worshiped the Emperor as a god. The Word Bearers had sought to spread their Cult of the Emperor to every world they added to the Imperium. But the Emperor deeply disliked and mistrusted organized religion (ironic, since he had often been the focus for much of it in his various guises across history), blaming it for much of the darkness that had plagued humanity's history. The Emperor openly and publicly refuted his alleged divinity and banned religious worship in his empire, and demanded that his subjects accept the "Imperial Truth"-- that science, reason and logic alone presented the tools required to create a better human future. Lorgar did not suffer the Emperor's reprimand or views on religion well. Angered and wounded that the Emperor would not accept his devotion and worship, Lorgar turned instead to the Ruinous Powers of the Warp -- who were all too willing to accept the devotion of one of humanity's Primarchs. Before long, the Word Bearers Legion had been almost entirely corrupted by the Chaos Gods, and Lorgar and Erebus were tasked by the Ruinous Powers with corrupting all of their fellow Space Marines -- starting with the greatest of them all, the Warmaster Horus.

During a battle against Chaos-spawned undead on Davin's moon, whose Planetary Governor, Eugen Temba, had been corrupted by the forces of the Chaos God Nurgle, Horus was poisoned by a xenos blade dedicated to Nurgle known as a Kinebrach Anathame that had been stolen from the human civilisation of the Interex by Erebus after Horus and the Luna Wolves of the 63rd Expeditionary Fleet had made a disastrous first contact with them. Erebus then gifted the weapon to the Chaos-corrupted form of the Imperial Army commander Eugen Temba who the Warmaster had left behind to govern Davin sixty years before. Temba had turned to the worship of Nurgle in the interim, being transformed into a bloated mutant and killing off most of his Imperial Army garrison in the process, transforming them into undead Plague Zombies that the Luna Wolves were forced to mow down in waves. Horus personally faced off with the mutant that had been Temba aboard the grounded ruins of his Imperial Cruiser. In the course of that battle, the potent living metal of the Chaos blade wielded by the plague-infused monstrosity left Horus with a bleeding, toxic wound in his shoulder that his Legion's Apothecaries could not heal despite all the advanced technology available to them. Seeing his chance to further the designs of Chaos, Erebus next persuaded the Luna Wolves' warrior lodge to allow a group of Davinite shamans -- Chaos Cultists all -- located on the surface of Davin at the Temple of the Serpent Lodge to heal him. The Luna Wolves, besides themselves with grief and the fear that their beloved Primarch would die, agreed to the suggestion, despite its direct violation of the creeds of the Imperial Truth.

During the dark rituals that followed within the temple, Horus' spirit was transferred from his body into the Immaterium. There, he bore witness to a nightmare vision of the future. He saw the Imperium of Man as a repressive, violent theocracy, where the Emperor and several of his Primarchs (but not Horus) were worshiped as Gods by the masses. While this vision of the Imperial future granted by the Chaos Gods was a true one, it was ironically an outcome largely created by the Warmaster's own actions. The Dark Gods portrayed themselves as victims of the Emperor's psychic might, and claimed that they had no real interest in the happenings of the material world. Magnus the Red, the sorcerous Primarch of the Thousand Sons Legion, had also travelled into the Warp via sorcery to try and stop Horus from turning to Chaos. Magnus explained that the Warmaster's vision was only one of many possible futures, but one that Horus alone could prevent. Horus, already jealous and resentful of the Emperor, proved all too receptive to the Ruinous Powers' false vision. The Chaos Gods' pact with Horus was simple: "Give us the Emperor and we will give you the galaxy." Driven by his jealousy, desire for power and anger at what he saw as his father's abandonment of him, Horus accepted the Ruinous Powers' offer. They healed his grievous wound and filled him with the powers of the Warp. Renouncing his oath to the Emperor, Horus led his Legion, renamed the Sons of Horus, into worship of the myriad Chaos Gods in the form of Chaos Undivided. He then sought to turn many of his fellow Primarchs to the service of Chaos, and succeeded with Angron of the World Eaters, Fulgrim of the Emperor's Children and Mortarion of the Death Guard, who were the first of many to follow, along with many regiments of the Imperial Army and several Titan Legions of the Adeptus Mechanicus.

Magnus the Red, the Primarch of the Thousand Sons Legion, foresaw Horus' actions through his Legion's own use of psychic sorcery, which had been forbidden to the Space Marines and the Primarchs by the dictates of the Council of Nikaea. Magnus then attempted to forewarn the Emperor of the impending betrayal of his favourite son. However, knowing that he would have to find a means of quickly warning the Emperor, Magnus used sorcery to send his message to the Emperor. The message penetrated the potent psychic defences of the Imperial Palace on Terra, shattering all the psychic wards the Emperor had placed on the Palace -- including those within His secret project in the Imperial Palace's dungeons, where He was proceeding with the creation of the human extension into the Webway. Refusing to believe that Horus, His most beloved and trusted son, would actually betray Him, the Emperor instead mistakenly perceived the traitor to the Imperium to be Magnus and his Thousand Sons, who had long suffered from a near-debilitating run of mutations because of the instability of Magnus' own genome as well as being practicioners of sorcery that brought them into constant contact with the dangerous entities of the Empyrean. The Emperor ordered the Primarch Leman Russ, Magnus' greatest rival, to mobilise his Space Wolves Legion and the witchhunters known as the Sisters of Silence and take Magnus into custody to be returned to Terra to stand trial for violating the Council of Nikaea's prohibitions against the use of sorcery within the Imperium. While en route to the Thousand Sons Legion's homeworld of Prospero, Horus convinced Russ, who had always been repelled by Magnus' reliance on psychic powers, to launch a full assault on Prospero instead even though Magnus had been entirely willing to face the Emperor's judgment once he realised he was being manipulated by the entities that called the Immaterium home.

Istvaan Massacres
Note: Published materials are inconsistent on their spelling of "Isstvan"; the more recently published material uses "Isstvan", while other (generally older) materials use "Istvaan". No explanation for this difference has been provided. For the sake of expediency, this article will use the spelling Istvaan, with no claims made to the accuracy of the spelling.

Istvaan III Atrocity
"Horus is the rightful Master of Mankind! He is the one who has led us to triumphs undreamed of. He is the one who has conquered ten thousand worlds. He will lead us in conquest of ten thousand more! Cast down the false Emperor! Hail the Warmaster!"

- Attr. Anonymous Traitor Legionary

Unknown to the Emperor, the Word Bearers Legion had been devoted to Chaos Undivided for some time before this event. The Imperial Planetary Governor of Istvaan III, Vardus Praal, had been corrupted by the Chaos God Slaanesh whose cultists had long been active on the world. Praal had declared his independence from the Imperium, and practiced forbidden sorcery, so the Council of Terra charged Horus with the retaking of that world, primarily its capital, the Choral City. This order merely furthered Horus' plans to overthrow the Emperor. Although the four Legions under his direct command -- the Sons of Horus, the World Eaters, the Death Guard and the Emperor's Children -- had already turned Traitor and now pledged themselves to Chaos, there were still some Loyalist elements within each of these Legions that approximated one-third of each force; many of these warriors were Terran-born Space Marines who had been directly recruited into the Astartes Legions by the Emperor himself before being reunited with their Primarchs during the Great Crusade. Horus, under the guise of putting down the religious rebellion against Imperial Compliance on the world of Istvaan III, amassed his troops in the Istvaan System.

Horus had a plan by which he would destroy all the remaining Loyalist elements of the Legions under his command, a plan that would ultimately unfold into the nightmare of what Imperial scholars would later name the Istvaan III Atrocity. After a lengthy bombardment of Istvaan III, Horus dispatched all of the known Loyalist Astartes down to the planet, under the pretense of bringing it back into the Imperium. At the moment of victory and the capture of the Choral City, the planetary capital of Istvaan III, these Astartes were betrayed when a cascade of terrible virus-bombs fell onto the world, launched by the Warmaster's orbiting fleet. Captain Saul Tarvitz of the Emperor's Children, however, was aboard his Legion's flagship Andronius and discovered the plot to wipe out the Loyalist Astartes of the Traitor Legions. He was able, with help from Battle-Captain Nathaniel Garro of the Death Guard who was in command of the Death Guard frigate Eisenstein, to reach the surface of Istvaan III despite pursuit and warn the Loyalist Space Marines he could find of all four Legions of their impending doom. Those that heard or passed on Tarvitz's warning took shelter before the virus-bombs struck. The civilian population of Istvaan III received no such protection: eight billion people died almost at once as the lethal flesh-dissolving virus called the Life-Eater carried by the bombs infected every living thing on the planet. The psychic shock of so many deaths at one time shrieked through the Warp, briefly obscuring even the Astronomican. The Primarch of the World Eaters, Angron, realising that the virus-bombs had not been fully effective at eliminating all the Loyalists, flew into a rage and hurled himself at the planet with 50 companies of Traitor Marines. Discarding tactics and strategy, the World Eaters Legion's Traitors worked themselves into a frenzy of mindless butchery. Horus was furious with Angron for delaying his plans, but the Warmaster sought to turn the delay into a victory and was obliged to reinforce Angron with troops from the Sons of Horus, the Death Guard, and the Emperor's Children. Fortunately, a contingent of Loyalists led by Battle-Captain Garro escaped Istvaan III aboard the damaged Imperial frigate Eisenstein and fled to Terra to warn the Emperor that Horus had turned Traitor.

On Istvaan III, the remaining Loyalists, under the command of Captains Tarvitz, Garviel Loken and Tarik Torgaddon, another Loyalist member of the Sons of Horus, fought bravely against their own traitorous brethren. Yet, despite some early successes that delayed Horus' plans for three full months while the battle on Istvaan III played out, their cause was ultimately doomed by their lack of air support and Titan firepower. During the battle the Sons of Horus Captains Ezekyle Abaddon and Horus Aximand were sent to confront their former Mournival brothers, Loken and Torgaddon. Horus Aximand beheaded Torgaddon, but Abaddon failed to kill Loken when the building they were in collapsed. Loken survived and witnessed the final orbital bombardment of Istvaan III that ended the Loyalists' desperate defence. To prove his worth and loyalty to Lord Commander Eidolon of the Emperor's Children -- and thus to his Primarch, Fulgrim -- Captain Lucius of the 13th Company of the Emperor's Children, the future Champion of Slaanesh known as Lucius the Eternal, turned against the Loyalists that he had fought beside because of his prior friendship with Saul Tarvitz. Lucius slew many of them personally, an act for which he was then accepted back into the Emperor's Children on the side of the Traitors. In the end, the Loyalists retreated to their last bastion of defense, only a few hundred of their number remaining. Finally, tired of the conflict, Horus ordered his men to withdraw, and then had the remains of the Choral City bombarded into dust for a final time from orbit.

Flight of the Eisenstein
"His dreams and hope are in ruin, his trust proved false, and his brightest son fallen to darkness. These are bitter tidings, a nightmare made flesh, but they must reach the Emperor."

- Battle-Captain Nathaniel Garro, Legiones Astartes Death Guard

Seventy Loyalists of the Death Guard Legion and the Imperial Saint Euphrati Keeler led by Battle-Captain Garro had commandeered the Imperial frigate Eisenstein and, evading the Traitor forces of Horus, were able to escape from the Istvaan System into the Immaterium, after being told what was happening on the planet. The Eisenstein was badly damaged by the Death Guard battleship Terminus Est during its escape from Istvaan III and it was assaulted by undead minions, including the first known Plague Marines of Nurgle while it was within the Immaterium. This assault by Warp entities forced the ship to make a crash emergence from the Warp. The repeated traumas left all of the frigate's astropaths dead, and its lone Navigator was mortally wounded. However, Garro managed to attract the attention of passing Loyalist starships by setting the vessel's Warp-Drives to self-destruct and ejecting them from the starship. Rogal Dorn's Imperial Fists Legion's massive mobile fortress-monastery Phalanx and the Legion's fleet had been becalmed in the Warp for some time due to the waxing power of the Ruinous Powers as the Heresy began, and his Navigators sensed the detonation of the Eisenstein's Warp-Drives. Charting an immediate course for the location of the detonation, Dorn met with Garro, who explained to him all that had happened with the Traitor Legions. Dorn was reluctant to believe Garro's tale, but overwhelming proof from a Remembrancer (journalist) named Mersadie Oliton who had escaped from Horus' flagship, the Vengeful Spirit, and Garro's dogged insistence finally convinced the Primarch. The Phalanx fortress set a course for Terra.

The fate of the Eisenstein's survivors is unknown. Sequestered on Luna in a tower belonging to the Sisters of Silence after their arrival in-system, Garro, the rest of his Loyalist Death Guard, Captain Iacton Qruze of the Luna Wolves, and the warriors of the Silent Sisterhood faced one of the Death Guard Marines named Solun Decius who had succumbed to the temptations of the Chaos God Nurgle after being infected with one of the Lord of Plague's more virulent illnesses now known as Nurgle's Rot by the undead minions Nurgle had unleashed on the Eisenstein. Seeking to end his pain, Decius allowed himself to become possessed by a Lesser Daemon of Nurgle, a variant Plaguebearer called the Lord of the Flies. Afterwards, Garro and Captain Qruze were met by Malcador the Sigillite, leader of the Council of Terra and the Emperor's Regent, who informed them that the Emperor had need of people who were strong of will and as "inquisitive" as they. Malcador ordered Garro to begin to comb the galaxy for 7 other Astartes from both the Traitor and Loyalist Legions who with him would become the founding members of the Imperial Inquisition and the militant arm of its daemon-hunting Ordo Malleus -- the Grey Knights.

Preparations and Allegiances
Much of Horus' later success arose from the thorough groundwork he had laid before the opening shots of the Heresy were fired at Istvaan III. He had already swayed the Primarchs Angron and Mortarion, of the World Eaters and Death Guard Legions, respectively, to the side of Chaos because of their own various personal grudges against the Emperor. Fulgrim of the Emperor's Children had been lured to the side of the Warmaster by the promise of power and personal perfection that the Chaos Gods, especially Slaanesh, offered to him and his vain Astartes. Lorgar of the Word Bearers, who had been responsible for the nascent rebellion and Horus's own corruption by Chaos, was also with the Warmaster. Three of the most loyal Legions who could not be swayed to the side of Chaos, the Dark Angels, Blood Angels and Ultramarines and their Primarchs, were sent on missions by the Warmaster far from Terra and the Istvaan System. The Imperial Fists and White Scars were too close to Terra to be contacted without raising suspicion, though Horus believed -- mistakenly -- that the White Scars' Primarch Jaghatai Khan, would ultimately take his side. Shortly before the Drop Site Massacre on Istvaan V, Fulgrim also attempted to sway his friend Ferrus Manus of the Iron Hands Legion to Horus' cause by using many of the same inducements that had been offered to the Adeptus Mechanicus, with whom the Iron Hands were closely allied in both temperament and philosophy. This attempt failed, and Fulgrim barely escaped with his life. Angered by the rebuff, Fulgrim promised he would deliver Manus' severed head to Horus in recompense, a promise he kept on Istvaan V. The Blood Angels were sent to the daemon-infested Signis Cluster and the Ultramarines to the world of Calth, where a large Word Bearers force, under First Captain Kor Phaeron, had massed to hold Roboute Guilliman's equally massive Legion in place while Horus made his play for Terra.

Of the other eventual Traitor Primarchs, Konrad Curze, the Night Haunter, was due to face disciplinary action from the Emperor which he did not believe he deserved; the Alpha Legion Primarch Alpharius had always been closer personally to his brother Horus than to his father the Emperor, although some evidence indicates that he and his twin brother Omegon's turn to Chaos was driven by mistaken loyalty to the Emperor; and the Iron Warriors' Primarch Perturabo's open and bitter rivalry with Rogal Dorn of the Imperial Fists and his feeling that he and his Legion were handed the worst tasks in the Great Crusade for which they never received the recognition they believed they were due made him an easy target for corruption.

The Thousand Sons had never planned to join Horus, but the path Tzeentch had mapped for that Legion and their potent psychic Primarch Magnus the Red ultimately led them to Chaos regardless. Unfortunately, the Space Wolves' unexpected assault on the Thousand Sons' homeworld -- a brutal campaign remembered as the Scouring of Prospero -- resulted in the destruction of the libraries of precious knowledge that Magnus and his fellow Thousand Sons held so dear. Mortally wounded by Leman Russ, Magnus fell to temptation as he watched Tizca, the capital city of Prospero and its famed libraries of ancient knowledge burn and he called out to the Chaos God Tzeentch to save both himself and the remains of his Legion. The God of Sorcery was only too happy to oblige and he transported Magnus and the Thousand Sons through the Warp to the Daemon World later known as the Planet of the Sorcerers. Magnus became a Daemon Prince of Tzeentch and now desired only vengeance against the Emperor for what he saw as a betrayal, never realizing that it was Horus who had truly engineered his downfall and corruption.

The remaining Space Marine Legions -- the Raven Guard, Salamanders, Iron Hands and Space Wolves -- remained staunchly loyal to the Emperor, though all but the Space Wolves would pay dearly for it in the battles to come. Beyond the Legions, Horus had already swayed Magos Regulus of the Adeptus Mechanicus to his side with promises of the Standard Template Construct (STC) databases of ancient technology recovered during the war with the Auretian Technocracy. This alliance delivered crucial Adeptus Mechanicus and Titan support to the Warmaster's Traitor Legion and Traitor Imperial Army forces.

Meanwhile, Horus and his confidante and mentor in the ways of Chaos, the Word Bearers' First Chaplain Erebus, conducted a ritual designed to communicate with the Chaotic entities of the Warp. They established contact with a daemon called Sarr'kell, who acted as an emissary of the Chaos Gods to Horus and the Traitor Legions. Horus was then deceived by the daemon into believing that the Chaos Gods had no interest in dominating the material universe, and were only lending their support so that Horus could overthrow the Emperor, who they claimed was creating devices that could destroy the daemonic beings of the Immaterium. Horus agreed, and promised to swear loyalty to Chaos Undivided after his fateful operations on Istvaan III.

Drop Site Massacre on Istvaan V
"It was treachery at first. To turn against brothers, to kill for personal advancement and power. But we have seen them, how their minds and bodies have been corrupted. Their very belief systems have been warped. This is no longer Horus's treachery. It is his heresy."

- Attributed to Roboute Guilliman, Lord of Ultramar and Primarch of the Ultramarines Legion

The Istvaan System’s third world, comfortably close enough to the sun to support human life, was now a virus-soaked mass grave marking the anger of Horus Lupercal. The world’s population was nothing more than contaminated ash scattered over lifeless continents, while the bones of their cities remained as blackened smears of burnt stone – a civilisation reduced to memory in a single day. The orbital bombardment from the Warmaster’s fleet, payloads of incendiary shells and virus-laden biological warfare pods, had seemingly spared nothing and no one anywhere in the world. Istvaan III lingered now in silent orbit around its sun, almost grand in the extent of its absolute devastation, serving as the scarred tombstone for the death of an empire.

Ringing Istvaan V was one of the largest fleets ever gathered in the history of the human species. Without a doubt, it was the most impressive coalition of Astartes vessels, with the scouts, cruisers, destroyers and command ships of seven entire Legions. With a precision that required mass calculation, the fleets of seven Astartes Legions hung in the skies above Istvaan V. Shuttles and gunships ferried between the heaviest cruisers, while the decks of every warship made ready to deploy their warriors in an unprecedented, unified planetfall. Horus, traitorous son of the Emperor, was making his stand on the surface. The Imperium of Man had sent seven Legions to kill its wayward scion, little knowing four of them had already spat on their oaths of allegiance to the Throneworld.

Aboard the Fidelitas Lex, Lorgar's flagship played host to a gathering of rare significance. There were commanders from the Night Lords, Alpha Legion, Iron Warriors as well as three additional Primarchs; Nighthaunter, Alpharius Omegon and Perturabo. Lorgar strode to the centre of the gathering of Traitors. He then proceeded to impress upon the gathering of his sons, brothers and cousin Astartes of the importance of their cause, and of the significance this day would hold in history. The Word Bearers and their allies believed that the Imperium had failed them and by being flawed to its core, imperfect in its pursuit of a perfect culture, and in its weakness against the encroachment of xenos breeds that sought to twist humanity to alien ends. And it had failed them, most of all, by being founded upon lies. The Imperium was forged by a dangerous deceit, and had eroded them all by demanding they sacrifice truth on the altar of necessity. This was an empire, propagated by sin, that deserves to die. And here, on Istvaan V, they would begin the purge. From the ashes would rise the new kingdom of mankind: an Imperium of justice, faith and enlightenment. An Imperium heralded, commanded and protected by the avatars of the gods themselves. An empire strong enough to stand through a future of blood and fire. The Emperor believes them loyal. Their four Legions were ordered to Istvaan V on His misguided conviction alone. But their coalition here and now was the fruit of decades’ worth of planning. It was ordained, and brought about according to ancient prophecy. No more hiding in the shadows. No more manipulating fleet movements and falsifying expeditionary data. From this day forward, the Alpha Legion, the Word Bearers, the Iron Warriors and the Night Lords would stand together – bloodied but unbowed beneath the flag of Warmaster Horus, the second Emperor. The true Emperor. First Captain Sevatar of the Night Lords Legion uttered, "Death to the False Emperor," becoming the first living soul to utter the words that would echo through the millennia. The curse was taken up by other voices, and soon it was being cried in full-throated roars. "Death to the False Emperor! Death to the False Emperor! Death! Death! Death!"

Thousands of Drop Pods and Stormbirds were deployed for the initial assault. The first wave was under the overall command of the Primarch Ferrus Manus and besides his own X Legion, the Salamanders led by Vulkan, and the Raven Guard under the command of their Primarch Corax joined him. Vulkan's Legion assaulted the left flank of the Traitors' battle line while Ferrus Manus, the Iron Hands' First Captain Gabriel Santor, and 10 full companies of elite Morlocks Terminators charged straight into the centre of the enemy lines. Meanwhile, Corax's Legion hit the right flank of the enemy's position. The odds were considered equal; 30,000 Traitor Marines against 40,000 Loyalists. Horus was aware of the location of the Loyalists' chosen drop site and his troops fell upon the Loyalist Legions.

The battlefield of Istvaan V was a slaughterhouse of epic proportions. Treacherous warriors twisted by hatred fought their former brothers-in-arms in a conflict unparalleled in its bitterness. The mighty Titan war engines of the Machine God walked the planet’s surface and death followed in their wake. The blood of heroes and traitors flowed in rivers, and the hooded Hereteks Adepts of the Dark Mechanicum unleashed perversions of ancient technology stolen from the Auretian Technocracyto wreak bloody havoc amongst the Loyalists. All across the Urgall Depression, hundreds died with every passing second, the promise of inevitable death a pall of darkness that hung over every warrior. The Traitor forces held, but their line was bending beneath the fury of the first Loyalist assault. It would take only the smallest twists of fate for it to break. The forces on the surface have been embattled for almost three hours with no clear victor emerging. Even now, the loyalists wait for the second wave of 'allies' to make planetfall, believing they would be reinforced for their final advance. The traitors all knew their parts to play in this performance. They are all aware of the blood they must shed to spare their species from destruction, and install Horus as the Master of Mankind.

Though the Iron Hands, Raven Guard and Salamanders had managed to make a full combat drop and secured the drop site, known as the Urgall Depression, they did so at a heavy cost. Overwhelmed with rage, the headstrong Ferrus Manus disregarded the counsel of his brothers Corax and Vulkan and hurled himself against the fleeing rebels, seeking to bring Fulgrim to personal combat. His veteran troops -- comprising the majority of the X Legion's Terminators and Dreadnoughts -- followed. What had begun as a massed strike against the Traitors’ position was rapidly turning into one of the largest engagements of the entire Great Crusade. All told, over 60,000 Astartes warriors clashed on the dusky plains of Isstvan V. For all the wrong reasons, this battle was soon to go down in the annals of Imperial history as one of the most epic confrontations ever fought.

The Urgall Depression was churned to ruination beneath the boots and tank treads of countless thousands of Astartes warriors and their Legion’s armour divisions. The loyal primarchs could be found where the fighting was thickest: Corax of the Raven Guard, borne aloft on black wings bound to a fire-breathing flight pack; Lord Ferrus of the Iron Hands at the heart of the battlefield, his silver hands crushing any traitors that came within reach, while he pursued and dragged back those who sought to withdraw; and lastly, Vulkan of the Salamanders, armoured in overlapping artificer plating, thunder clapping from his warhammer as it pounded into yielding armour, shattering it like porcelain.

The traitorous primarchs slew in mirror image to their brothers: Angron of the World Eaters hewing with wild abandon as he raked his chainblades left and right, barely cognizant of who fell before him; Fulgrim of the lamentably-named Emperor’s Children, laughing as he deflected the clumsy sweeps of Iron Hands warriors, never stopping in his graceful movements for even a moment; Mortarion of the Death Guard, in disgusting echo of ancient Terran myth, harvesting life with each reaving sweep of his scythe.

And Horus, Warmaster of the Imperium, the brightest star and greatest of the Emperor’s sons. He stood watching the destruction while his Legions took to the field, their liege lord content in his fortress rising from the far edge of the ravine. Shielded and unseen by his brothers still waging war in the Emperor’s name. At last, above this maelstrom of grinding ceramite, booming tank cannons and chattering bolters – the gunships, drop-pods and assault landers of the second wave burned through the atmosphere on screaming thrusters. The sky fell dark with the weak sun eclipsed by ten thousand avian shadows, and the cheering roar sent up by the loyalists was loud enough to shake the air itself. The traitors, the bloodied and battered Legions loyal to Horus, fell into a fighting withdrawal without hesitation.

The second wave of "Loyalist" Space Marine Legions descended upon the landing zone on the northern edge of the Urgall Depression. Hundreds of Stormbirds and Thunderhawks roared towards the surface, their armoured hulls gleaming as the power of another four Astartes Legions arrived on Istvaan V. Yet the Space Marine Legions of the reserve were no longer loyal to the Emperor, having already secretly sworn themselves to Chaos and the cause of Horus. The Night Lords of Konrad Curze, the Iron Warriors of Perturabo, the Word Bearers of Lorgar Aurelian, and the Alpha Legion of Alpharius represented a force larger than that which had first begun the assault on Istvaan V. The secret Traitor Legions mustered in the landing zone, armed and ready for battle, unbloodied and fresh.

The Iron Warriors had claimed the highest ground, taking the loyalist landing site with all the appearance of reinforcing it through the erection of prefabricated plasteel bunkers. Bulk landers dropped the battlefield architecture: dense metal frames fell from the cargo claws of carrier ships at low altitude, and as the platforms crashed and embedded themselves in the ground, the craftsmen-warriors of the IV Legion worked, affixed, bolted and constructed them into hastily-rising firebases. Turrets rose from their protective housing in the hundreds, while hordes of lobotomised servitors trundled from the holds of Iron Warriors troopships, single-minded in their intent to link with the weapons systems’ interfaces. The Word Bearers bolstered their brother Legions on one flank of the Urgall Depression while the Night Lords took positions on the opposite side. Down the line, past the mounting masses of Iron Warriors battle tanks and assembling Astartes, First Captain Sevatar of the Night Lords and his First Company elite, the Atramentar took up defensive positions. Both the Word Bearers and the Night Lords were to be the anvil, while the Iron Warriors would be the hammer yet to fall. The enemy would stagger back to them, exhausted, clutching empty bolters and broken blades, believing their presence to be a reprieve. Dragging their wounded and dead behind them, Corax and Vulkan led their forces back to the drop site to regroup and to allow the warriors of their recently arrived brother Primarchs of the second wave a measure of the glory in defeating Horus. Though they voxed hails requesting medical aid and supply, the line of Astartes atop the northern ridge remained grimly silent as the exhausted warriors of the Raven Guard and Salamanders came to within a hundred metres of their allies. It was then that Horus revealed his perfidy and sprung his lethal trap. Inside the black fortress where Horus had made his lair, a lone flare shot skyward, exploding in a hellish red glow that lit the battlefield below. The fire of betrayal roared from the barrels of a thousand guns, as the second wave of Astartes revealed where their true loyalties now lay. Ferrus Manus looked on in stunned horror as Fulgrim laughed at the look on his brother's face as the forces of his "allies" opened fire upon the Salamanders and Raven Guard, killing hundreds in the fury of the first few moments, hundreds more in the seconds following, as volley after volley of Bolter fire and missiles scythed through their unsuspecting ranks. Even as terrifying carnage was being wreaked upon the Loyalists below, the retreating forces of the Warmaster turned and brought their weapons to bear on the enemy warriors within their midst. Hundreds of World Eaters, Sons of Horus and the Death Guard fell upon the veteran companies of the Iron Hands, and though the warriors of the X Legion continued to fight gallantly, they were hopelessly outnumbered and would soon be hacked to pieces. The Iron Hands had damned themselves by remaining in the field.

The Raven Guard front ranks went down as if scythed, harvested in a spilling line of detonating bolter shells, shattered armour and puffs of bloody mist. Black-armoured Astartes tumbled to their hands and knees, only to be cut down by the sustained volley, finishing those who fell beneath the initial storm of head- and chest-shots. Seconds after the first chatter of bolters, beams of achingly bright laser slashed from behind the Word Bearers as the cannon mounts of Land Raiders, Predators and defensive bastion turrets gouged through the Raven Guard and the ground they stood upon. The Iron Warriors and Word Bearers kept reloading, opening fire again, hurling grenades and prepared to fall back. The Word Bearers Legion had taken up landing positions on the west of the field, ready to sweep down and engage the Raven Guard from the flank.

The Raven Guard were confronted by the treacherous Word Bearers, with their Primarch Lorgar, the First Captain Kor Phaeron and the First Chaplain Erebus at their vanguard. The two Legions fought one another in bitter combat. In the midst of this battle, the Word Bearers unleashed the elite unit known as the Gal Vorbak -- Astartes who had allowed themselves to be possessed by daemons. They attacked the Raven Guard's Primarch en masse, but despite the advantage of their numbers, Corax's formidable abilities as a consummate warrior proved to be more than a match for the possessed Astartes, and he slew them with impunity. Seeing the slaughter of his most favoured sons, Lorgar intervened and prevented the death of the remaining Gal Vorbak Astartes. The two opposing Primarchs then duelled one another in close combat, and the Raven Guard's Primarch quickly gained the upper hand over his outmatched brother. Lorgar had always been more of a scholar than a warrior and Corax prepared to execute him for his betrayal of the Emperor. Lorgar was spared from execution by the intervention of the Night Lords' Primarch, Konrad Curze, at the last moment. The Night Haunter and the Raven fought a brutal melee. Curze quickly gained the upper hand over his battle-weary brother and prepared to slay him, but Corax managed to escape death by taking to the sky with his master-crafted Jump Pack.

The outnumbered Loyalists were then surrounded and brutally butchered. Refusing to surrender, the remaining Raven Guard and Salamanders Astartes stubbornly defended themselves, trying to hold off the inevitable slaughter for as long as possible. Though they suffered an atrocious number of casualties, the Loyalists managed to hold their own, until the Primarchs Mortarion of the Death Guard and Angron of the World Eaters joined the fray. Bolstered by the support of the infamous Imperator-class Titan Dies Irae, the Traitors killed tens of thousands of Loyalist Astartes. At the height of the massacre the Warmaster Horus entered the fray, at the head of the elite Sons of Horus Terminators known as the Justaerin, slaughtering the Loyalists in wrathful anger.

Any hope for escape for the Loyalists was quickly crushed when the traitorous Iron Warriors destroyed the first wave's drop ships. The Loyalist starships still orbiting the embattled planet were also largely annihilated by the vastly superior numbers of the Traitor's fleet. Despite the odds arrayed against them, some of the Loyalists on the ground managed to survive against these odds—they miraculously escaped through the tightening cordon of Traitors that surrounded their position. The Raven Guard fared better than the Salamanders in escaping the brutal massacre. But the Salamanders managed to assist a few surviving Astartes from the decimated Iron Hands Legion to also escape the slaughter. Imperial history does not record the fate of these surviving Salamanders or their missing Primarch Vulkan. The Raven Guard's Primarch just barely managed to board a fleeing Thunderhawk gunship to make good his escape, but was thwarted in the attempt when it was shot down almost immediately by the gunfire of the Traitors. The badly damaged ship crashed on the outskirts of the Urgall Plateau.

Raven's Flight
Corax had survived the crash and quickly ordered the remaining warriors of his Legion to regroup. He learned to his shock that a large percentage of his Legion had been utterly annihilated during the ensuing slaughter. They took to the highlands of the surrounding hills and took to the shadows, hiding from their relentless pursuers. During their flight, their position was nearly discovered by a roving armour column of traitorous Iron Warriors, but they were destroyed in a Raven Guard ambush and wiped out before they could report what they had learned.

Thirty days after the initial planetary assault, the future looked grim for the fleeing Raven Guard survivors. They had received no word from either the surviving Iron Hands or Salamanders Legions. Corax ordered his warriors to dig-in and hold position at Lurgan Ridge while he undertook a lone reconnaissance of their original drop site to determine their options. Utilising his innate psi-abilities to escape detection, Corax successfully conducted a reconnaissance of the Traitor Legions' positions around the heavily fortified drop site. Though the Primarch informed his men that his mission was to reconnoiter the drop site, his primary objective was to scour the Urgall Plateau for the bodies of his fallen sons, but he failed to find them.

After 98 days of relentless pursuit, the Raven Guard survivors were finally backed into a literal corner. Caught upon the windswept mountainside, Corax's Legion remained resolute. Behind the peak stretched the great salt plains that had forced them into this last, defiant stand. Ahead of them massed the might of the World Eaters, the rage-driven Astartes Legion of Angron, who strode at their head roaring for the blood of his brother. A sea of white and blue World Eaters Astartes spattered with the red of gore swept up from the valley intent on the destruction of the Raven Guard. Maddened by their neural implants and driven into a battle-frenzy by inhuman cocktails of stimulants, the berserk warriors of the World Eaters pounded up the sloping mountainside while their tanks and guns provided covering fire; every warrior bellowed his eagerness to fulfill the blood oaths he had sworn to his Primarch.

But before they could utterly eradicate the surviving Raven Guard Astartes, the World Eaters were attacked from an unexpected quarter. Broad-winged aircraft plunged down from the scattering of clouds, missile pods rippling with fire. A swathe of detonations cut through the ranks of the World Eaters, ripping through their advance companies. Incendiary bombs blossomed in the heart of the approaching army, scattering white-hot Promethium over the steep slopes. Corax looked on with incredulity as blistering pulses of plasma descended from orbit, cutting great gouges into Angron’s Legion.

The roar of jets became deafening as drop ships descended on pillars of fire: black drop ships emblazoned with the badge of the Raven Guard. The Legionaries scattered to give the landing craft space to make planetfall. As soon as their thick hydraulic legs touched the ground, their ramps whined down and boarding gateways opened. The Raven Guard met their rescuers in stunned disbelief. These drop ships were part of a desperate rescue mission that had been devised by Commander Branne, a Raven Guard Captain who had been left in charge of the Legion’s homeworld of Deliverance. Without further delay the Raven Guard survivors quickly prepared for embarkation and escaped aboard the drop ships, breaking for orbit and leaving behind the frothing berserkers of the World Eaters, their angry Primarch futilely baying for blood.

Horus Triumphant
"The road to Terra is open. The time has come for us to take the war to the Emperor in his most impregnable fastness! We will make immediate preparation for the invasion of Terra and an assault on the Imperial Palace. Make no mistake, and it will be ours, my brothers! This will be no easy task, for the Emperor and his deluded followers will fight hard to prevent us from interfering with his plans for godhood. Doubtless much blood has yet to be spilled, theirs and our own, but the prize is the galaxy itself...Are you with me?"

- Warmaster Horus, Master of Istvaan

After the killing had stopped and the dead were gathered into great funeral pyres across the broken desert of the Urgall Depression, the once-grey skies of the planet burned orange with the reflected glow of a thousand pyres. The firelight bathed the rippling, glassy sands in a warm radiance, and towering pillars of black smoke from the burning corpses filled the air. Thousands of Astartes loyal to Horus gathered before a great reviewing stand, constructed by the Tech-priests of the Dark Mechanicus with astonishing speed. As the sun began to sink beyond the horizon, the smooth black planes of the stand shone with a blood red glow. The stand was erected as a series of cylinders of ever decreasing diameter, one standing atop another. The base was perhaps a thousand metres in width, constructed as a great grandstand upon which the Sons of Horus stood, their pre-eminent position as the elite of the Warmaster in no doubt after this great victory. Each warrior bore a flaming brand, and the firelight cast brilliant reflections from their armour.

Atop this pedestal of flame was another platform, occupied by the senior officers of the XVI Legion. Above the senior officers of the Sons of Horus stood the Traitor Primarchs. The sheer magnificence of such a gathering of might was breathtaking. Seven beings of monumental power stood on the penultimate tier of the reviewing stand, their armour still stained with the blood of their foes, their cloaks billowing in the winds that swept the Urgall Depression. Finally, the uppermost tier of the reviewing stand was a tall cylinder of crimson that stood a hundred metres above the Primarchs. Horus stood on top of it, his clawed gauntlets raised in salute. A furred cloak of some great beast hung from his shoulders, and the light of the corpse pyres reflected from the amber eye upon his breastplate. The Warmaster was illuminated from below by a hidden light source, bathing him in a red glow that gave him the appearance of the statue of a legendary hero, as he stood looking down on the endless sea of his followers from the towering platform. As the sun finally dipped below the horizon, a flight of assault craft roared over the Urgall Hills, their wings dipping in salute to the mighty warrior below. Solid waves of cheering crashed against the reviewing stand, howls of adulation torn from tens of thousands of throats. No sooner had the aircraft passed overhead than the massed Astartes began to march around the reviewing stand, their arms snapping out and hammering their breastplates in salute of the Warmaster. At some unseen signal a flame ignited on the northern slopes of the Urgall Depression and a blazing line of phosphor leapt across the ground in a snaking arc that described the outline of an enormous blazing eye upon the hillside. The adulation soared to new heights as the Eye of Horus seared itself into the sands of Isstvan V, the Warmaster’s forces roaring themselves hoarse in his praise. Super-heavy tanks fired in salute of Horus, and the towering immensity of the Dies Irae inclined its massive head in a gesture of respect. The ashes of the dead fell like confetti over Horus' mighty army as thousands of Traitor Astartes cheered, their cries of "Hail Horus! Hail Horus!" resounding long into the darkness.

Barely a handful of Loyalist Space Marines escaped with their lives from Istvaan V to bring dreadful word of the further betrayal of four more Space Marine Legions to the Emperor. A critically wounded Corax made the dangerous journey through the Immaterium back to Terra, arriving 133 days after departing the Istvaan System and finally reaching the Sol System -- the heart of the Imperium -- to seek audience with the Emperor. Vulkan was missing and presumed dead, though he would later reemerge after a harrowing journey back to Terra himself, to lead his Legion once more. The Salamanders, along with the Iron Hands and the Raven Guard, would spend the remainder of the Horus Heresy rebuilding their decimated Legions and were too weakened to play any further role in the great conflict.

In the days after the battle, the Traitor Legions salvaged a large number of vehicles, wargear and other war materiel from what the Loyalist Legions had left on the field. This salvage was repaired and modified for the Traitor Legions' use and then put back into frontline service to be used against the Imperium. Some of this equipment would still be in service with certain Chaos Space Marine warbands in the late 41st Millennium. Orbital space around Istvaan V was busy as the vessels of 8 Legions assumed formation prior to transit to the system jump point. Over 3,000 vessels jostled for position above the darkened fifth planet, their holds bursting with warriors sworn to the service of Horus. Tanks and monstrous war machines had been lifted from the planet with incredible efficiency and an armada greater than any in the history of the Great Crusade assembled to take the fire of war into the very heart of the Imperium.

In the days after the Drop Site Massacre, Horus called for a conclave of the Primarchs of all 8 of the Traitor Legions aboard his flagship, the Vengeful Spirit. Five of the Primarchs, including four who had fought at Istvaan V, met in person, including Horus, Fulgrim, Angron, Mortarion and Lorgar. Three appeared through the use of hololithic emitters that transmitted their signals through the Warp, including Perturabo, Night Haunter and Magnus the Red, who had only recently joined the Traitors after the Scouring of Prospero when the broken remains of his XV Legion had been transported by Tzeentch into the Eye of Terror to the Planet of the Sorcerers. The Thousand Sons, bitter at what they perceived as their betrayal by the Emperor, now willingly became the eighth Traitor Legion. The council of Traitor Primarchs made their plans for the next step in their war against the Emperor and then each Legion went its way according to its assigned role.

The fleets of Angron, Fulgrim, Mortarion, Lorgar and Horus' own Legion would rendezvous at Mars, now that word had come from the Tech-priest Regulus, the Mechanicus' liaison with the 63rd Expeditionary Fleet, of that planet’s fall to Horus’ supporters within the Mechanicus during the internecine conflict known as the Schism of Mars. With the manufacturing facilities of Mondus Gamma and Mondus Occullum wrested from the control of the Emperor’s forces, the forges of Mars were free to supply the Warmaster’s army. The eager warriors of the Alpha Legion were singled out by Horus for a vital mission, one upon which the success of the entire venture could depend. Following Horus' manipulation of Leman Russ into assaulting the homeworld of the Thousand Sons, the Space Wolves were known to be operating in the region of Prospero. In the nearby system of Chondax, the White Scars of Jaghatai Khan were sure to have received word of Horus’ rebellion and would no doubt attempt to link up with the Space Wolves. Horus could not allow such a grave threat to appear, and so the warriors of Alpharius were to seek out and attack these Legions before they could join forces.

The Night Haunter’s fleet had already departed, bound for the planet of Tsagualsa, a remote world in the Eastern Fringe that lay shrouded in the shadow of a great asteroid belt. From there, the Night Lords’ terror troops would begin a campaign of genocide against the Imperial strongholds of Heroldar and Thramas, star systems that, if not taken, would leave the flanks of the Warmaster’s strike on Terra vulnerable to attack. The Thramas System was of particular importance, as it comprised a number of Mechanicus Forge Worlds whose loyalty was still to the Emperor. This campaign would also serve to tie up the dreaded Dark Angels Legion, so that the forces of the Lion wouldn't be brought to bare against Horus and his upcoming campaign against Terra.

The ships of the Iron Warriors prepared to make the journey to the Phall System where a large fleet of Imperial Fists vessels were known to be regrouping after a failed attempt to reach Istvaan V in time to join the Loyalist assault. Though Rogal Dorn’s warriors had played no part in the Drop Site Massacre, Horus could not allow such a powerful Loyalist force to remain unmolested. The enmity between bitter Perturabo and proud Dorn was well known, and it was with great relish that the Iron Warriors set off to do battle with their old rivals. With his flanks covered and the Space Marine forces that could potentially reinforce the heart of the Imperium soon to be embroiled in war, the Traitors were ready to unleash 7 Terran years of devastating civil war upon the Imperium in the name of Horus and the Dark Gods.

Disposition of the Traitor Legions
Much remains uncertain in regards to the strategic positions, deployments and configuration of the forces loyal to the Warmaster Horus in the early phases of the war, and even their full scope and extent cannot be ascertained with any genuine certainty by the historian. Perhaps a full half of the Titan Legions and the numberless hosts of the Excertus Imperialis -- hundreds of millions of soldiers, vessels and war machines -- had either through corruption, misguided loyalty to Horus or simple blind ignorance in compliance with their orders, sided with the Warmaster. But this alone would never be enough to overthrow the Emperor. A thousand Battleships might be wrecked against the defences of Terra, ten million Auxilia might spend their lives in besieging the Eternity Gate, and ten millions follow them, and again and again, but Horus knew this alone would never avail him. Not against the superhuman warriors who held it; not against the Legio Custodes and defences designed by the Emperor's own hand and garrisoned now by Rogal Dorn and his sons, the Imperial Fists. So it was that the greatest attention should be placed on the location and strengths of the Traitor Legions. The Legions at the Warmaster's side during this period at the start of the conflict comprised eight Legions. The shattered remnants of the Thousand Sons, who would later join the Traitor's cause in earnest, were not yet at this time fully active in the war, and were still largely of unknown disposition and even allegiance following the apocalyptic Battle of Prospero. Although the Drop Site Massacre had inflicted terrible wounds on the Loyalist forces involved, the Traitor Legions had not themselves come away from the cataclysm unscathed which, combined with losses suffered during the recent purging of the Traitors' ranks at Istvaan III and elsewhere, had weakened Horus' position from its notional strength when the die for war was cast.

Hard facts regarding the operational Legiones Astartes numbers are impossible to ascertain, but credible estimates place Traitor losses during the battles of the Istvaan, Phall and Paramar Systems in the region of 100,000 Space Marine fatalities, compared to an unknown number, perhaps three or four times as high, as a death toll for those who remained loyal to the Emperor. This, by many estimates, left something in the region of 900,000 Legiones Astartes under arms in the Warmaster's cause, with perhaps two thirds or more of that figure in the Loyalist camp. This estimate, however, was still far from certain, one which is itself further distorted by the events that were to shortly unfold on Calth and Signus Prime. From this calculation -- as equivocal as it is -- it is possible to determine that even after the Drop Site Massacre, the military advantage Horus had yet gained was simply not large enough in scale to make an immediate and direct assault on Terra and the Imperial heartlands of the Segmentum Solar, roused as they were now against attack, a strategically viable option, let alone one that would guarantee victory. This was the reality that Horus faced in determining his next move.

The Traitor Legions were the single greatest power and strength of Horus' armies, but they were far from alone. To achieve the ultimate aim of laying siege to Terra and casting down the Emperor, the Traitors would have to call upon and fight alongside a wide array of other forces, some simply obeying the will of masters of long association, while others were brought into the Warmaster's fold through bribery, pacts of alliance, coercion or the infamous progress of the Dark Compliance. As early as the Traitors' defence of the Urgall Depression during the Istvaan V Drop Site Massacre, mortal Auxilia troops were used with unspeakable callousness by their Space Marine masters, herded towards the enemy as bullet-soaks on which the foe's ammunition would be expended before battle was truly joined, and such disregard for the purely human component of the Warmaster's forces would be shown time and again throughout the bloody years that were to follow. This was not however universal, as at other times, Horus and his principal subordinates entrusted vital missions to the more reliable of his mortal allies, and split entire battlegroups of Traitor Auxilia and Armada units on independent operations either of conquest or destruction, although it was not uncommon for him to assign an officer or cadre of the Sons of Horus, Iron Warriors or Alpha Legion to oversee such forces in the field.

The Traitor Auxilia
"Fear not that I am come to demand your surrender. There is in me no such gift of mercy. I am come to deliver not words, but fire."

- Baron Armelan, Emissary of the Warmaster to the planetary council of Subinus

By far the largest numbers of human troops under the Warmaster's command were drawn from the Imperial Auxilia, and ranged from the massive Imperial Army Regiments of the Line to the elite ranks of the Solar Auxilia. In addition to these experienced and well-equipped forces, the Warmaster also exercised command over native militias, planetary tithe-hosts and Rogue Trader Conquestor companies. The latter were able to range far and wide, often serving as emissaries of the Warmaster and delivering in person demands for Planetary Governors to swear loyalty to his cause, or suffer the ruin of their worlds. Some accounts even suggest Traitor Rogue Trader Conquestor forces continued their exploration of the outer darkness even as the Heresy consumed the Imperium, claiming untold worlds not in the name of the Emperor, but of the Warmaster. Some even established pocket empires far beyond the Imperium, crowning themselves as the Warmaster's suzerains over realms that lingered beyond the Heresy and well into the age of the Great Scouring.

The Traitor Fleets
In addition to these ground forces, Horus' mighty host was bolstered still further by entire fleets of warships turned to his service, whether willingly or otherwise. The need for such a vast armada only became apparent after the events of Istvaan when the shortest route to attack Terra was no longer available, and the wars of the so-called Age of Darkness had begun. Without an aggressive expansion in the number of Warp-capable voidcraft in the Traitors' hands, Horus' war would simply not have been possible, for while the Legiones Astartes controlled their own ships, and thousands more besides as part of the great Expeditionary Fleets, in scale alone they were insufficient to move and supply the vast hosts of all kinds that Horus had now gathered under his banner and to fight the battles flaring up across a war zone that encompassed the galaxy entire. To ensure the continued service of these vessels and their crews when seperated from his Legions' direct control, the Warmaster emplaced within them numerous hidden agents, cults, spies and assassins. Many a Traitor shipmaster who attempted to renege on his oaths to Horus whilst thinking himself beyond the Warmaster's gaze, found himself cut down by a deck officer who was in fact a sworn agent of Horus, while those who displayed ruthless ambition in the Warmaster's service or who embraced the strange and sinister teachings promulgated by the dark forces that walked in Horus' shadow were rewarded.

The Dark Mechanicum
Aside from the human component in the Traitors' ranks, the powers of the Mechanicum and their kin were also of great importance to the war. Within the ranks of this "Dark Mechanicum," as they became known, could be found powerful elements of the Martian Priesthood, the Ordo Reductor and the Legio Cybernetica, along with many of the feared Myrmidon Destructor Cults and a number of sub-cults which had operated for long years on the edge of tech-heresy, all drawn together by Fabricator-General Kelbor-Hal. With them had come the support of more than half of the legions of the Titanicus as well as dozens of allied Knight Houses, and now Mars itself was lost to the Loyalists, while the output and military power of Forge Worlds such as Sarum, Voss, Cyclothrathe and Stygies had declared for the Traitors, with others such as Anvilus, Incaladion and Ryza paralysed by civil war.

Hidden Forces
As the fires of the Heresy consumed ever greater swathes of the Imperium, other, less conventional forces fought alongside the Traitors. Aside from the legions of long-implanted spites, agents, terrorist cells and mercenaries, many were cultic in origin. These were drawn from the vast numbers of fanatics steeped in the insanity of the Immaterium that were rising up on world after world where the disciples of the Dark Apostle Erebus and the Davinites that had followed in the Warmaster's wake -- among others -- had seeded unspeakable blasphemy before the war. Most were frenzied zealots who threw themselves upon their erstwhile lords screaming the praises of entities then unnamed, but which became all too familiar as the Heresy ground on. Few worlds were untouched by the presence of these deluded cults, but it is notable that many of the Traitor Space Marines avoided direct contact with them. The Word Bearers in particular factored the cult forces into their battle plans, and it is notable that many appeared to venerate the warriors of Lorgar as demi-gods or angels, prostrating themselves upon the ground in their pesence or laying down their own lives in battle without question.

There was one further ally Horus could call upon, one most often encountered where the Warp cults had previously risen up or where the greatest amounts of blood had been shed, though as the war ground on, incursions grew ever more widespread and unpredictable. These were the entities of the Warp, known by some by the ancient and arcane term "Daemons," though many of the Imperium's savants thought of them instead as aliens that simply existed within the Immaterium much as the dreaded parasite Psychneuein did, or as psychic phenomena -- mortal insanity given physical, albeit temporary form with the rise in Warp Storm activity across the galaxy. Few perceived the true danger or power of such creatures, nor would they for some time yet. Eventually, many of the Traitor Legions would fight side by side with the legions of the abyss, sharing their sins and chanting the names of the same dark powers. But at the time of the Warmaster's conquest of the northern Imperium, most of the Legiones Astartes, with the notable exception of the Word Bearers, still considered them anathema to their principles or disregarded them as mere dangerous Warp phenomena, although particularly within the ranks of the Emperor's Children that was rapidly changing, even in the early years of the Age of Darkness. The truth -- often now overlooked -- is that for many years after the battles of Istvaan, most of the Traitor Legions were concerned more with a political rebellion and with imposing a new order on the Imperium than with surrendering it to the anarchy and Warp-rent Chaos that would descend in the latter years of the Heresy.

Disposition of the Loyalist Legions
"The measure of true glory is not to give battle in the bright noon of war, surrounded by brave comrades upon the field of victory, but to valiantly fight on alone in darkness, with no hope of aid or even remembrance, and to spit defiance in midnight's eye."

- Lion El'Jonson, Primarch of the Dark Angels Legion, Reflections in the Mirror of War, Vol. III

In the aftermath of the Drop Site Massacre, the Imperium was plunged into a period of anarchy that future historians would know as the "Age of Darkness." To those still loyal to Terra, all had at a stroke been cast into confusion, for none could tell who was ally and who Traitor, and so grievous a blow had been dealt, it called into question the Imperium's survival itself. Increasingly, the Warp was in turmoil, making voyages across the void hazardous and protracted, while communication by astrotelepathy over any extended distance was all but impossible. This left the defenders of the Imperium sundered from each other, shorn of direct contact and separated not simply by distance, but by insurmountable hazards and vulnerable to attack. For Rogal Dorn, on whose shoulders the fate of Terra and possibly the entire Imperium rested, this was a period of intense frustration as he attempted to assay his forces and coordinate their stand. Though the remnants of the Imperial Fists at Terra benefitted from the vast military assets located there, including such elite forces as the Legio Custodes and the powerful Armada Imperialis Battlefleet Solar Saturnyne shipyards. Mars, however, having risen in civil war in support of the Warmaster, was now forbidden to the Loyalists, and worse yet had become a deadly thorn in the Emperor's side, needing constant watchful blockade, and so further diverted Dorn's attention. The decision was taken for him to concentrate on building Terra's defences for the inevitable Traitor onslaught to come.

Shattered Legions
"We must learn to pace ourselves. Tactical restraint. To hit and run, and not to be greedy and trust in overwhelming power as of old. We must learn the tactics and techniques of those thrown in with us and respect them. We must take our iron and alloy it with the mettle of the others who were shattered alongside us. We must mix our broken strength with other broken strengths to forge a new, unbroken edge."

- Captain Shadrak Meduson, 10th Company, Sorrgol Clan, Iron Hands Legion

The fate of Corax and his Raven Guard is well-documented, but of the other Legions betrayed during the Drop Site Massacre, still less was known for certain. Corax had confirmed the bitter news of the death of his brother Ferrus Manus of the Xth Legion at the hands of their brother Fulgrim of the Emperor's Children, news that had shaken Malcador and the members of the Council of Terra to the core. Of the Iron Hands Legion itself, it was known that many had been driven to stark madness by witnessing their father's end and thrown themselves wholesale into the crucible of war as if to absolve their loss in their own deaths. Yet, a substantial number of Iron Hands Legionaries had extricated themselves from the massacre, and while few had made it off the surface, many more had survived the calamitous void ambush of the Legion's fleet, breaking away and scattering across the stars. Some would form isolationist bands, fighting their own private wars against the Traitors, such as the infamous "Red Talons" of Autek Mor, or refuse any master save their own will as did the company known to some records as the "Heart of Stone." Others, such as those who came to follow Shadrak Meduson, would form a series of ad-hoc, cell-structured forces slowly cohering into a single loosely knit organisation; a shattered Legion army shot through with elements of other forces that had been wrecked by the base treachery at Istvaan.

Of the fate of the Legiones Astartes Salamanders, still less was known. Witnesses had watched in horror as the entire sector in which the last of the XVIIIth had fought was consumed in atomic fire. Of all three Legions betrayed at the Drop Site Massacre, the Salamanders suffered the worst, scant few of their number escaping. Of these, most would join the bitter shadow-war against the Traitors either as part of shattered Legion warbands, or more rarely as coherent forces of their own entirely, such as those who followed the so-called "Prophet of Fire," at the Siege of Mezoa and the liberation of Goth, while the small guard force of Nocturne acted in the aggressive defence of their native region in accordance to their oaths, continuing to raise recruits in their Primarch's name and their Legion's traditions unchecked. Of the Primarch Vulkan, it was assumed through much of the Age of Darkness, incorrectly, that he had perished.

Hunter-Killers
As Loyalist survivor forces scattered across the northern Imperium and beyond, the Warmaster tasked certain elements to hunt them down and slaughter them to a man. Such orders were invariably accompanied by an implicit or explicit threat -- return in victory or do not return at all. Thus, these hunter-killer forces were as isolated from their own chains-of-command as the Loyalists they tracked, and soon a bitter and bloody war developed between hunter and hunted. While most of the Traitor Legions contributed forces to this effort, the Legion that embraced the task with the most relish was undoubtedly the Emperor's Children, those elements not accompanying their Primarch commanding hunts which scoured the void and inflicted unspeakable atrocities upon those Loyalists they were able to corner.

The Sundered and the Black
"I should rather fall in honour and glory than live in dishonour and treachery, but in truth that decision is not mine to make. Rather, it has been made for me, by one I once held above all others and whose name shall never pass my lips again."

- Unidentified Blackshield, thought formerly of the Sons of Horus

Almost from the outset, the war of the Horus Heresy was a vast cataclysm and one whose events moved with such quicksilver pace that mystery, supposition, lies and simple ignorance cloaked much of the bloodshed even as it occurred, casting a veil over much that would never be lifted. Though the roll call of Space Marine Legions, Titan Legio, Auxilia regiments and Mechanicum Taghmata that sided with the Arch-Traitor and those who remained loyal is largely known and accepted, the full truth is far more complex and far more mysterious than commonly believed.

Of those who fell at Istvaan, there were survivors, remnants and fleeing fragments shorn of command and driven half mad by treachery; from that point onwards they were isolated, alone. These were the shattered Legions and, while some swiftly returned to the Imperial fold, some did not or would not. Some would go on to wage a bitter war of vengeance alone, some would simply disappear, their fates unknown, their stories untold. But there were others of a darker hue. It has long been refuted since, but is indelibly the case, that in the Legions that remained loyal to the Emperor there were elements, sometimes whole companies and commands, that did not. In some cases the infection of the Warmaster's "Warrior Lodges" has been blamed, while in others perhaps grievances long-smouldering were the cause, just as infiltration by outside forces, or simply a darker truth applies that, given the option, some Astartes believed Horus had the superior cause and the superior right to command their allegiance, not the Emperor, while some retained a loyalty to their Emperor and the Great Crusade over that of their own Primarch's will. It is true that particularly in the early years of the war, detachments of Legiones Astartes and sometimes entire squadrons of warships simply vanished without apparent trace, and while many may have fallen foul of Warp Storms and enemy action, it is likely just as true that some quietly slipped anchor and turned their coats to serve another master, and that this happened on both sides of the divide.

Thus can perhaps be explained, at least in part, persistent stories and evidence long since suppressed of midnight clad warriors in defaced Night Lords heraldry savagely attacking Traitor forces at the liberation of Estaban III, or of recurring reports of multiple Space Marine strike forces seemingly in the resurrected livery of the Dusk Raiders thwarting the Iron Warriors at Kibron and Malinche's Fall. Likewise also should be considered the long-denied evidence of a Great Company of the Space Wolves Legion bearing the symbol of the Serpent's Eye slaughtering millions at Neo Cadiz in 008.M31, or of a company of Legiones Astartes present at the Siege of Mezoa bearing the hybrid arms and panoply of the Iron Hands and Sons of Horus Legions both. These were merely a handful of still infamous cases, but there are many more unsubstantiated or simply now forgotten which paint a more complex and uncertain picture of this great civil war than is normally accounted. Further to this, and perhaps an even more sinister enigma, are the persistent reports of Space Marine forces appearing bearing no sign or seal of heraldry or origin at all, or stranger yet, heraldry which bears no mark known during the Great Crusade, although whether the "black" Legionaries were merely turncoats or, as some have whispered, perhaps raised by the Traitors from the chimeric gene-seed of the Istvaan dead for their own terrible purposes, none can now say for certain.

The term "Blackshield" came to be used during the period of the Horus Heresy known as the Age of Darkness in the early 31st Millennium to cover a wide range of Space Marine outcasts, marauders and those Legiones Astartes of uncertain allegiances or origin. Mystery and suspicion attached themselves to such warriors regardless of their true loyalties or intentions, and while some did deliberately scour their old heraldry from their armour or replace it with some false device or heraldry of their own, their name of Blackshield was often a literal description for armour over-masked or simply scorched black.

Though never existing in numbers so great as the Legions from which they had no doubt sprang -- far from it -- each faction and band, from the dozen survivors of a deadly betrayal by their own kind who cast aside the past, to the cohort of rapidly indoctrinated initiates thrust into battle for a cause they barely understood in Power Armour empty of livery, had their own place in the tapestry of galaxy-wide destruction that was the Horus Heresy.

The motivations and goals of those forces dubbed Blackshields by the warlords of the era and the historians of later times were as individual as their bands. Many ultimately can be categorised as believing (rightly or wrongly) that their Legion or Primarch was no more, or on the opposite side of the coin renounced their Legion and their sire, refusing to follow his example in siding with one faction or the other in Mankind's galactic civil war. In such ways did so-called "traitors" draw Traitor blood and -- albeit more rarely -- did scions of Legions that remained steadfastly loyal turn upon their Emperor and their brothers. The more shadowy and less understood of the Blackshield factions remained cloaked under a shroud of misdirection and secrecy. These were Legionaries created using dangerously accelerated or forbidden chimeric gene-seed implantation and brutally expedited psycho-indoctrination protocols to quickly replace catastrophic losses as the certainties of the early years of the war gave way to the grim realisation that neither side might have enough Space Marines and materiél to overwhelm the other, and while many programs were put into place for the Legions to accelerate recruitment by the Legions themselves, other, darker and more hidden endeavours were undertaken by the powers of both sides outside the "legitimate" framework of the Legions that had gone before, uncaring of established practice or traditions, or indeed risk, needing only results.

Of those Blackshields who were truly rogue, many still fought their war with a bitter fervour that matched any zealot in either the Warmaster's or the Emperor's cause. While others, perhaps starting on their path through a simple drive to survive, became reavers and renegades intent upon forging their own destinies among the stars. Of these some began to corrode in mind and spirit as time and the tide of war ground on, degenerating into little more than madmen and wanton killers, while others eventually regained a place, although often a distrusted one, in the order of battle of one great faction or the other before the end. Of those who did not, most would find the Great Scouring that was to follow their bloody ending, or be driven into the darkness beyond known space.

Loyalists Scattered
War now spread the length and breadth of a chaotic and now largely unseen Imperium, and as far as Rogal Dorn and Malcador the Sigillite were concerned, the Imperial Fists alone of all the Legiones Astartes would have to shoulder the burden of the defence of the Throneworld of Terra. Until such time as the Warp Storms relented or those Legions still unknowingly enacting the Warmaster's duplicitous orders could fight their way through to them, the defenders of Terra would stand alone while around them the galaxy burned.

Uncertainty and Allegiance
The treachery of the Legions that prosecuted the Drop Site Massacre was a stark crime against all the Great Crusade had striven so hard to achieve, and the names of these Traitor Legions spread far and wide. From the very beginning, however, the division between Loyalist and Traitor was never as clearly defined as later generations might believe. The nature of the Emperor's immense Great Crusade was such that, while each of the Legions often fought as a whole army under the direct leadership of its own Primarch, smaller contingents were detached across the entire Imperium and into the deep void beyond. Space Marine detachments of all sizes, from individual squads to entire battalions operated beyond even the reach of the Warmaster's agents whilst the poison was spreading through their parent Legions. In most cases, these contingents were simply too far distant to be infected with the malady of treachery. By the time they eventually returned to communication range with the Imperium at large, such as it was with astrotelepathy made all but impossible by the tortured Warp, the die was cast and events had moved on. Confronted with outright betrayal, these contingents saw the Warmaster for what he truly was and their brothers for base traitors, and could do nothing but renounce their erstwhile kin.

Despite the paucity of records, accounts of small warbands that were once part of the known Traitor Legions fighting independently persisted throughout the war. A handful of extant accounts, now sealed beyond all retrieval, make reference to a loosely-termed and non-formal class of warrior known as the "Blackshields." The majority of Blackshields appear to have been of the Legiones Astartes, though some may once have belonged to other factions. In some cases the term was literal description, the warriors having obscured the livery of their armour's panels black to hide all former associations. In other cases, outcast forces proudly bore their original colours and may have regarded themselves as the true inheritors of their Legions. Thus, for example, the 34th Millennial of the Emperor's Children (the "Death Eagles") bore the original purple and gold of their parent Legion with pride, refusing to abandon their heraldry. It is thought that the Death Eagles Millennial clashed with their Traitor kin at Lethe and at Revorthe Keep in the Coronid Deeps, but their ultimate fate, like that of so many others, remains unknown.

The Dark Compliance
"The slave cares not whose hand wields the whip or why, knowing only the authority of its touch, the discipline of its voice and the certainty of pain."

- A Cthonian Proverb On many worlds, the seeds of corruption had been sown long before the hand of betrayal struck at Istvaan. When the Warmaster led his forces in civil war, hundreds of worlds not directly connected to his power base declared for his cause. On these planets and dominions, many scattered around the dangerous periphery of the Imperium's frontiers, it was because his agents and those of his allies within the Mechanicum, the Alpha Legion and the Word Bearers had already poisoned their hearts against the Emperor. There would be many hundreds more, from isolated and otherwise unimportant colonies to keystones of the Imperium's economy and military strength, that would fall under his sway as the war progressed in a process that became known as the "Dark Compliance." To each world over which the Warmaster's shadow fell, a simple choice was given; total submission and surrender or total destruction and brutal subjugation -- slavery or death, there were no other options and no second chances. It was a perverse parody of the progress and glorious goals of the Great Crusade, but served as more than mere scorn for the Emperor's dream or even the vainglory of a tyrant, for there was underlying method and intelligence beneath the apparently wanton savagery. When one militant world or stubbornly Loyalist star system was punished by apocalyptic destruction for their brave defiance, such fear was created in others nearby that their surrender came as a rapid and forgone conclusion, often without a shot fired in their defence. Each world added not simply territory but manpower, production capacity and supply, feeding a Traitor war machine that was growing exponentially in power. Further, those worlds marked for death -- where possible -- can be seen with hindsight to have been more measured if no less brutal decapitation strikes for which Horus' own Legion had long been famed. It can also be observed that the devastation visited during the Dark Compliances was never so thorough that survivors were not left to spread the word of what terrors they had beheld, and of the price this new shadow emperor executed for defiance.

Execution Team
After learning of Horus' perfidy on Istvaan III, the Sires and Siresses of the various secret Imperial Assassin Clades were tasked by Malcador the Sigillite, the secret Master of Assassins, with the daunting task of slaying the Arch-Traitor Horus, for if they could accomplish this monumental undertaking, they could effectively crush the nascent rebellion against the Emperor before it could inflict further damage upon His Imperium. But every assassination attempt against the Warmaster had failed thus far. Though the operatives sent by the Clades were their finest students and equal to the task, every attempt had resulted in failure. The Assassins had thrown their most gifted students into a meat-grinder, sending them in blind and half-prepared. Every strike against Horus was broken, and he had shrugged off each attempt without notice. Every time the Clade masters met, they were forced to grimly listen to a catalogue of each other's failures.

After the last failed attempt by Clade Venenum, a new strategy was decided upon. With the advice of a special guest in the form of Constantin Valdor, the Captain-General of the Legio Custodes who served as the personal protectors of the Emperor, the masters of the Clades realised that their mission plans were not flawed, they were simply not enough. No single Assassin, no matter how well-trained, no matter which Clade they hailed from, could ever hope to terminate the Arch-Traitor alone. But a collective of killers, a strike team consisting of an elite unit of killers hand-picked for the task, might be enough to succeed. There had never been a precedent for such an initiative, for the Emperor would have never sanctioned assassination as an official Imperial policy. The deployment of an Assassin was a delicate matter and never one taken lightly. In the past, the Clades had fielded two or three of their operatives on a single mission when the circumstances were most extreme, but these Assassins were always drawn from the same Clade, and even this occurred only after much deliberation. Yet in this crucial and extreme instance, Malcador, serving as Director Primus of the Clades, decided that more drastic measures were needed to accomplish the Assassins singular goal. He authorised the creation of the first Imperial Execution Force.

Horus did not adhere to the rules of war, nor did he baulk at the use of a tactic because it offended sensibilities. At Istvaan III he had bombed his sworn brethren, his own warriors even, into obliteration. Nothing, no mater how vile, was beyond him. It was decided by the Assassins that if they were to kill this foe, the could not limit themselves to the moral abstracts that had guided the Clades in the past. They had to dare to exceed them. And so a select strike team of Assassins was formed. An Execution Force, the first of its kind. Six Assassins, one from each Clade, were gathered together and given the select task of killing Horus by any means necessary. In the meantime, the Dark Apostle Erebus had decided on a bold course of action of his own. He firmly believed that as long as the Traitor Legions followed Horus, all would be as it should and as the Dark Gods had promised. Victory would come soon enough, perhaps even sooner than any of them might expect, for after the latest assassination attempt on the Warmaster, Erebus had come to realise a truism of warfare: if a tactic could be used against Horus, then it could also be used by the Traitors against the Emperor.

"Black Pariah"
Within Imperial history, only one "Black Pariah" has ever existed. He was a former Imperial Assassin by the code-name of "Spear." Born as a human Untouchable, he was captured by the Silent Sisterhood and brought to Terra, where the Clade Culexus experimented upon and augmented him in an attempt to create a more powerful and deadly form of Culexus Assassin. It is not known whether these augmentations or his unnatural abilities made him a "Black Pariah." Spear was eventually deemed too unstable and dangerous by his Clade's masters to be left alive. He was placed in the care of the Sisters of Silence and was sent aboard one of their lone vessels, bound for the heart of a nearby sun. Unfortunately, this vessel was intercepted by a Traitor vessel carrying the Dark Apostle Erebus of the Word Bearers Legion. Boarding the Sisters' vessel, the Word Bearers killed all aboard, with the exception of Spear.

Sensing the usefulness of such a unique specimen, Erebus found a new purpose for his captive. He forced Spear to undergo a painful and vile Chaotic ritual, in which a minor daemon from the Immaterium was bonded with the former Imperial Assassin. This bonding created a highly dangerous apex predator -- a "counter-psyker" -- capable of redirecting a psyker's attack directly back upon him. In order to utilise this ability, the "Black Pariah" first had to obtain a sample of his target's blood. This was a necessary component that helped him synchronise with his target's psionic abilities in order to reflect their attacks. Two standard years later, following the events of the Drop Site Massacre on Istvaan V, Erebus tasked his deadly minion to assassinate the Emperor. Spear spent an inordinate amount of time in order to painstakingly reach his ultimate goal -- a document that possessed a minute drop of the Emperor of Mankind's precious blood. Spear eventually obtained this document upon the world of Dagonet, which would bring him into direct conflict with the Imperial Execution Force.

Dagonet
As the Horus Heresy progressed and word filtered throughout the galaxy of Horus' galactic uprising, numerous worlds began to erupt into anarchy as the populations began to split over whether they should remain loyal to the Emperor or join the Warmaster. Dagonet was one such world, where Horus Lupercal was second only to the Emperor in being celebrated by the people of the planet; statues in Horus' honour were raised everywhere, and the Dragoneti spoke of him as "the Liberator." As the historic record went, in the early years of the Great Crusade, Dagonet had languished under the heel of a corrupt and venal priest-king who ruled the planet through fear and superstition. Horus, at the head of his Luna Wolves Legion, had come to Dagonet and freed the world -- accomplishing the deed with only one round of ammunition expended, the single shot he fired that dispatched the tyrant. The victory was one of the Warmaster's most celebrated triumphs, and it ensured he would be revered forever as Dagonet's saviour. The Dagoneti clans had started the uprising against the Imperium when the Heresy began. The Imperial Governor issued a formal statement of support for the cause of Horus. The world's nobles had declared in favour of Horus and rejected the rule of Terra. The common people were the ones fighting back in the name of the Emperor. There was blood in the streets of the Dagoneti capital city as soldiers fought soldiers and militia fought clan guards. Those who could flee the star system filled every starship they could get their hands on. It was small wonder that the aristocratic clans who now ruled the planet would give their banners to Horus instead of a distant Emperor who had never set foot on their world.

The Execution Force soon learned the future whereabouts of where Horus would be. Agents of the Imperium operating covertly in the Taebian Sector report a strong likelihood that Horus was planning to bring his flagship, the Vengeful Spirit, to the planet Dagonet in order to show his flag. The Clades believed that the Warmaster’s forces would use Dagonet as a foothold from which to secure the allegiance of every planet in the Taebian Stars Sector. Dagonet was a keystone world in the politico-economic structure of the Taebian Sector, and if it fell fully under the shadow of Horus, then it would mark the beginning of a domino effect, as planet after planet along the same trade axis followed suit. Every Loyalist foothold in this sector of space would be in jeopardy. One Imperial vessel would be able to slip through the Warp to Dagonet, far easier than an entire reprisal fleet. Six Assassins, the best of their Clades, could bring death. The Execution Force would embed on Dagonet and set up multiple lines of attack. When Horus arrived there, they would terminate his command with extreme prejudice. Horus' assassination at this juncture would throw the Traitor forces into disarray and break the rebellion before it could advance on to the Segmentum Solar.

The Execution Force successfully circumvented all detection and was able to secretly arrive upon Dagonet. The Execution Force gathered intelligence to determine what exactly had occurred on Dagonet. In the first moments of the insurrection, desperate signals had been sent to the Space Marine Legions and their Legion fleets; but these had gone unanswered. Both the starships of the admiralty and the Legions had battles of their own to fight, far from the Taebian Stars. They would not intervene. For all the fire and destruction the collapse of Dagonet and its sister worlds might cause, there were larger conflicts being addressed; no crusade of heroes was coming to ride to the rescue. The civil war on Dagonet was a rout, and it was those who stood in the Emperor's name who were dying. Across the planet, the forces that carried Horus' banner were only days away from breaking the back of any resistance. Dagonet was already lost. The turncoat nobility on this planet did not need to see Horus to adhere to his banner. His influence hung over Dagonet like an eclipse blotting out the sun. They were fighting in his name in fear of him, and that was enough. And when the Traitors finally won, Horus' work would be done for him. This same thing was happening all across the galaxy, on every world too far from the Emperor and the rule of Terra. When Dagonet fell, Horus would turn his face from this place and move on, his advance one step closer to the gates of the Imperial Palace.

While gathering intelligence and deciding upon the best course of action, two of the Execution Force's number decided to set about on a different course of action. The Venenum Assassin Jenniker Solam had become distracted by her mission with the plight of the local Loyalist Dagoneti who continued to wage their desperate war against the pro-Horus planet's nobility. The Dagoneti introduced her to the forbidden writings of the Lectitio Divinitatus which postulated the worship of the Emperor of Mankind as a divine being, the one, true God of humanity. Solam became a willing convert of this nascent religious movement and vowed to help the Dagoneti with their plight. Her interest in helping the people of Dagonet and her new spirituality created friction with the rest of the Execution Force, and so she took her leave, and the mission to assassinate Horus continued on without her. The Culexus Assassin Iota, who showed great interest in Solam's quest, followed her. The pair of Assassins soon came into conflict with the "Black Pariah" known as Spear. Realising the dire threat of such a creature, the two Assassins attacked the Traitor Assassin. In the ensuing battle Solam was mortally wounded. Iota utilised her Animus Speculum, unleashing her innate anti-psyker abilities upon Spear, seriously wounding him in the process. Though Iota finally gained the upper hand, her efforts were for naught, as Spear was able to sample a drop of her spilt blood. This enabled the Traitor Assassin to engage his genetic lock, using his own innate abilities to reflect Iota's attack back onto her, boiling the Assassin in the crucible of her own powers.

The dying Solam was found by her brother Eristede Kell, a Vindicare Assassin and the Execution Force's team leader. Solam made Kell promise to kill the Traitor Assassin, not out of vengeance, but for the sake of the God-Emperor. The Execution Force managed to salve Iota's memory coil from her Animus Speculum and review her confrontation with the creature known as Spear. Realising the dire threat that this Counter-Assassin represented, the Assassins' mission became twofold; assassinate Horus and kill the creature that had murdered their comrade.

Moment of Truth
The Sons of Horus Legion finally arrived in-system at Dagonet. The Vengeful Spirit settled in orbit above the world of Dagonet. The vessel had brought a military force of such deadly intent and utter lethality that the planet and its people had never known the like, in all their recorded history. And it was only the first. Other warships were following close behind. This was the visitation granted to Dagonet by the Sons of Horus, the tip of a sword blade forged from shock and awe. Far below, on the planet's surface, across the white marble of Liberation Plaza, a respectful hush fell over the throng of people who had gathered. A pregnant hush fell over the Dagoneti, as they looked to the sky and awaited the arrival of their redeemer, the owner of their new allegiance. Their war-god, the Warmaster Horus. At this time, the Execution Force was in place. The Vindicare Assassin Kell waited in the perfect assassin's perch, ready for the Warmaster's arrival. The Callidus passed a measuring gaze over the nervous lines of Dagoneti Planetary Defence Force soldiers and the robed nobles standing back on the gleaming, sunlit steps of the great hall. Governor Nicran was there among them, waiting with every other Dagoneti for the storm that was about to break. Suddenly, there was a blast of fanfare from the trumpets of a military band, and Governor Nicran stepped forward. When he spoke, a Vox-bead at his throat amplified his voice. "Glory to the Liberator!" he cried. "Glory to the Warmaster! Glory to Horus!" The assembled crowd raised their voices in a thundering echo.

The Sons of Horus teleported onto the planet's surface. The tallest of the superhuman warriors, his battle gear decked with more finery than the others, stepped forward. He was covered with honour-chains and combat laurels, and about his shoulders he wore a metal dolman made from ores mined in the depths of Cthonia; the Mantle of the Warmaster, forged by Horus' captains as a symbol of his might and unbreakable will. He drew a gold-chased Bolt Pistol, raising it up high above his head; and then he fired a single shot into the air, the round crashing like thunder. The same sound that rang about Dagonet on the day they were liberated. Before the empty shell casing could strike the marble at his feet, the crowd were shouting their fealty. Glory to Horus! The towering warrior holstered his gun and unsealed his helmet, drawing it up so the world might see his face. This was the moment of truth. The Vindicare Assassin placed his crosshairs on the centre of the scowling grille of the Warmaster's helmet. There was no hesitation, no margin for error. The Assassin fired his Exitus Rifle. The shot struck the target in the throat, reducing the flesh to atoms, superheating the fluids into steam, boiling skin and vapourising bone. The only sound was the fall of the headless corpse as it crashed to the ground, blood jetting across the white marble and the Warmaster's shining mantle. Horus was dead.

But the Assassins of the Execution Force had been duped. Horus had sent a surrogate, a sacrificial proxy. The Vindicare had killed Luc Sedirae, the Captain of the Sons of Horus' 13th Company. Though the warrior Kell shot wore the mantle of the Warmaster, the unique robe belonging to the Primarch himself, it had all been a ruse. In their anger, the Sons of Horus turned upon the populace of Dagonet and began to slaughter them in earnest.

Amidst the chaos and anarchy of the massacre of the entire populace of Dagonet, Kell finally tracked Spear down and with the assistance and sacrifice of his fellow Assassin, managed to finally draw out and kill the "Black Pariah." Kell found himself was the lone survivor of the first Imperial Execution Force. The Vindicare Assassin departed Dagonet and decided to make one last attempt on the Warmaster's life. He made a suicidal attack on Horus' flagship. Kell set his own ship on a direct course for the Vengeful Spirit's command bridge, where he seemed to meet his own fate when he ejected himself into space once he reached his intended target, in an ultimately vain attempt to land a desperate shot at Horus while he stood looking out of the Battle-Barge bridge's armoured observation deck into space. The Execution Force's assassination attempt had failed.

In the aftermath of the events on Dagonet, Horus confronted Erebus within his private chambers. He chastised the Dark Apostle for his audacious plan to assassinate the Emperor, declaring that when the opportune moment finally dawned, it would be him -- and him alone -- who killed the Master of Mankind.

The Talon Closes Around Manachea
What came to be known as the Conquest of Manachea was a campaign carried out by those under the direct command of the Warmaster Horus during the latter part of 007.M31. It was both an early example of the Warmaster turning his forces to seize entire sectors of the Imperium he deemed valuable, and a demonstration of the speed and brutality with which such campaigns were accomplished. It could be seen in retrospect to have provided a template for scores of such campaigns which came after it, both in terms of strategy and the savage consequences involved for those worlds which fell into the Traitors' grasp throughout the time of the Age of Darkness. The Conquest of Manachea, led personally by Horus and his inner cadre of commanders, was itself the centerpiece of an interlinked series of campaigns, fleet actions and local wars which swept like storms through the celestial region sometimes referred to as the Coronid Thule, or the Coronid Deeps, between 006.M31 and 008.M31. This region, which encompasses the frontier border areas of the Segmentum Obscurus and Ultima Segmentum, and constituted some of the most industrialised regions of the northern Imperium at the time, had been effectively cut away from regular direct contact with the Segmentum Solar owing to the rising tide of Warp turbulence which would culminate in the so-called "Ruinstorm," which followed on from the dark events at Calth in 007.M31.

Battle of Calth
While Horus made his plans for what would become known as the infamous Drop Site Massacre on Istvaan V, the Warmaster sent word to the XVII Legion’s Primarch Lorgar that the time had come for his Astartes, the Word Bearers, to strike against the Imperium. The Warmaster was keenly aware of the bitter hatred that Lorgar had for his Primarch brother Roboute Guilliman and his XIII Legion, the Ultramarines, who had once humiliated the Word Bearers by destroying their city of Monarchia on the world of Khur at the Emperor's orders during the Great Crusade. The Ultramarines had taken no pleasure in this act, which was intended to teach Lorgar and his Astartes to adhere to the atheistic doctrines of the Imperial Truth rather than spread the false belief that the Emperor was divine to all the worlds that they conquered. Yet Lorgar and the Word Bearers had never forgiven the Ultramarines for this action and they longed for vengeance against the XIII Legion.

Horus told Lorgar that he had fed Guilliman false intelligence in regard to a possible threat within the Veridian System in the Segmentum Tempestus, far to the galactic south of Terra. This supposed threat stemmed from the Orks of the Ghaslakh Empire. Horus had ordered the XIII and the XVII Legions to muster and meet at the world of Calth in the Ultramarines' Realm of Ultramar, in order to conduct a massive joint campaign of extermination against the Ghaslakh xenohold, a common mission for the Astartes during the final days of the Great Crusade.

It would be at Calth that Lorgar would launch a surprise attack on the Ultramarines whilst they were gathered for the campaign against the Orks of Ghaslakh. The XIII Legion would be caught completely unaware while the Word Bearers would use the advantage of surprise to completely annihilate their hated rivals. The assault at Calth would also allow the Word Bearers to reveal that they, too, now served Ruinous Powers. Calth was not chosen as the site of the confrontation between the Word Bearers and the Ultramarines by chance, for the Word Bearers intended to destroy one of the jewels in the Ultramarines' realm of Ultramar (then known as the Ultramar Coalition), just as the XIII Legion had destroyed one of the Word Bearers' greatest achievements, the sacred city of Monarchia, four decades earlier.

Horus ordered the majority of the XVII Legion to Ultramar, and the dark powers of the Warp gave them sure and swift passage across the increasingly restless Immaterium. As the Word Bearers entered Ultramar space, Lorgar prepared his Legion for the inevitable slaughter that would follow. Command of the main assault force was given to Kor Phaeron, the First Captain of the XVII Legion and one of Lorgar’s most favoured champions. Calth was to be Kor Phaeron’s operation to execute, far more than it was Lorgar’s. Kor Phaeron had planned the assault of Calth for his Primarch meticulously, and executed it with the aid of the Dark Apostle Erebus. The punishment and annihilation of the XIII Legion was the campaign's principal aim; the humiliation and execution of Lorgar's hated rival Roboute Guilliman was a secondary objective. But for Lorgar, the assault would also mark his first opportunity to gain true favour in the eyes of the Dark Gods he now served; to prove to them that he had earned his place as their Chosen One.

Cull of the Word Bearers
Unknown to Erebus and Kor Phaeron, their Primarch had also had a secret objective in mind when he had sent his two most zealous sons to Calth. After their humiliation at Khur, thousands of World Bearers within the Legion detested the Ultramarines. The Urizen ordered a great gathering of his Legion while their fleet was already en route to Calth. The Primarch called for Argel Tal, the leader of the Gal Vorbak, and one other Word Bearers officer who would eventually become commanders and apostles amongst the elite Vakrah Jal. The Primarch wanted their counsel on what to do with those amongst their Legion he no longer trusted. The Word Bearers had culled their ranks down through the decades, removing such unrepentantly Loyalist elements such as the Terran-born warriors of their Legion, but had carried out no purge like the Istvaan III Atrocity that Angron was so proud of. Lorgar knew that the loyalty of his own Legion to both him and his vision of Mankind transformed through an embrace of Chaos was never in doubt, but competence was another matter entirely. Lorgar asked what should be done with those warriors of the XVII Legion he felt were no longer reliable. Those whose hatred burned brighter than their sense. For tens of thousands of them -- whole companies, whole Chapters -- their rage was no longer pure. It was decided that these suspect elements of the Legion would be gathered into a single host and ordered to undertake the "sacred" mission to Calth to assault the Ultramarines that they had so craved. They would be led by such zealots as First Chaplain Erebus, the Dark Apostle Kor Phaeron and Fleet-Captain Zadkiel and were expected to martyr themselves in glory. The other Traitor Legions such as the Emperor's Children, Sons of Horus and the World Eaters might have purged their own ranks at Istvaan III, but the Word Bearers had proceeded to purge their own at Calth.

Furious Abyss
At the same time that Lorgar had concentrated his Legion's offensive on Calth, a separate assault by the XVII Legion on the Ultramarines' homeworld of Macragge had been prepared, using a massive prototype Battleship specially constructed by Horus' allies in the Mechanicum before the start of the Heresy known as the Furious Abyss. The Furious Abyss was manned by one thousand Astartes, a full Chapter split into ten companies, each a hundred strong. All heeded the Word of Lorgar. These Legionaries were led by Fleet-Captain Zadkiel, a devout and zealous follower of the Word. He was charged by the Dark Apostle Kor Phaeron to lead the assault upon the world of Macragge, where they would strike the first blow against the hated Imperium of Man. Had it succeeded in reaching Macragge, the Furious Abyss would likely have annihilated the planet, the remaining two Chapters of the Ultramarines Legion garrisoned there, and the stores of precious gene-seed in the XIII Legion's fortress-monastery, the Fortress of Hera. Fortunately, the Furious Abyss was intercepted in the void before it reached Macragge by an ad hoc force led by the Ultramarines Captain Lysimachus Cestus and was destroyed, though at the cost of every Loyalist Space Marine's life.

Calth Atrocity
Before Horus had made his break with the Emperor of Mankind public at Istvaan III, he had sought to lure away as many Loyalist Legions from Terra as possible. Horus had ordered Roboute Guilliman to lead an expeditionary force to the world of Calth in the Veridian System in the Realm of Ultramar to prepare for a campaign in the Eastern Fringes of the galaxy, where, Horus claimed, an Ork WAAAGH! was massing. Horus expected the Ultramarines to await the arrival of the Word Bearersm who would join with the XIII Legion in prosecuting a camapign against the Ork menace. Unknown to Guilliman, XVII Legion had long before turned Traitor in service to the Chaos Gods, and its Primarch, Lorgar, gleefully accepted Horus' orders to close the trap on his Legion's long-hated rivals. The Word Bearers' sudden attack decimated Guilliman's Legion fleet, and the Ultramarines' ground troops quickly found themselves impossibly outnumbered by their former allies as the infamous Battle of Calth erupted. The Word Bearers slew their Loyalist foes in droves in the early stages of their surprise attack and pushed them back over huge stretches of territory. The Traitors rejoiced at the terrible blows they were inflicting upon the Legion that had once aided the Emperor in humiliating them upon the world of Khur decades before the start of the Heresy when they had been taken to task for repeated violations of the atehistic philosophy known as the Imperial Truth. Unknown to them, Guilliman's flagship, which had survived the initial Word Bearers' attack on the Ultramarines fleet, effected emergency repairs and regrouped with the other surviving Ultramarine starships in space. Having taken stock of his remaining forces, Guilliman sent an immediate astropathic distress call to Macragge.

The Loyalist Marines on Calth, Ultramarines all, had been forced into a fighting retreat, but soon occupied fortified positions. Many Ultramarines had been born on Calth, and proved more resolute than the Word Bearers anticipated. In space, Guilliman's vessels began hit-and-run attacks on their over-confident enemy. Guilliman assessed his ground troops' positions and broadcast clear, concise orders to each pocket of defence, coordinating them into a cohesive force. One Ultramarine force led by Captain Ventanus led a breakout and retook Calth's Defence Laser silos, aiding the sorely-pressed Ultramarines fleet from the surface of Calth. Guilliman's depleted forces slowed the Word Bearers down long enough for the remainder of the Ultramarines Legion to arrive and rout the Traitor Marines from the system, though at a heavy cost. The Word Bearers turned Calth's own orbital defence platforms on the Veridian star, stripping away the outer layers of its photosphere and destabilising it, ultimately rendering the surface of Calth uninhabitable. At the same time, the Word Bearers had used the battle taking place on Calth to summon a massive Warp Storm called the Ruinstorm, that was intended to cut off Ultramar from the rest of the galaxy and prevent the Ultramarines from providing any reinforcements to Terra as Horus made his assault upon humanity's homeworld. The eruption of the Ruinstorm cut off Calth from the main body of the Ultramarines Legion and left the Astartes of the XIII Legion trapped on Calth locked in a brutal subterranean war with those Word Bearers units that had also been left behind when their Legion retreated from the Viridian System. Yet Roboute Guilliman and a large portion of his Legion had remained off-world as a result of the Word Bearers' devious assault upon the Ultramarines fleet. Bloodied but unbowed, the Ultramarines received the orders of Malcador the Sigillite, the Emperor's Regent, while he was in disposed pursuing the secret Imperial Webway Project, and prepared to meet the needs of the Imperium's defence against the Traitor Legions as best they could.

The Word Bearers' use of Calth's orbital defence platforms against Calth’s sun destabilised it, tore away the outer layers of its photosphere and threatened to cause it to explode as a supernova. The Veridian System's star, its colour changing from a bright yellow to an angry blue as its internal composition shifted, immediately suffered a flare trauma, and shortly after unleashed massive solar flares that irradiated Calth with lethal levels of radiation and stripped away its once dense oxygen-nitrogen atmosphere. The surface of Calth was no longer a safe environment for human habitation or any form of organic life, nor was it possible to evacuate the planet's remaining population in time. Therefore, Captain Ventanus sent out a warning over the planetary Vox and data network to all citizens, soldiers of the Imperial Army, Astartes of the XIII Legion, and any other loyal servant of the Imperium, to move with all haste to the subterranean arcology or arcology system closest to them. The arcology systems offered sufficient protection for the remaining inhabitants of Calth and their defenders to survive the wave of solar death that was about to engulf their world. This message successfully reached many millions of people who successfully took shelter within Calth's underground warrens, which had originally been built to free up more land for agricultural cultivation. It would take several Terran years for the remnants of the Ultramarines fleet to return to the Veridian System after the Loyalist survivors rode out the storm. Unfortunately, the Forces of Chaos left on the planet also fled underground as well. Vetanus vowed that the Ultramarines and their allied Loyalist forces would continue to fight until every last Traitor on Calth had been exterminated. Thus began the phase of the conflict that would be remembered as the Underworld War.

Yet, despite the Loyalists' last-minute victory and the survival of the Ultramarines Legion and its Primarch, the Forces of Chaos could consider their assault on Calth a success. The XIII Legion had been badly crippled and no longer presented a viable threat to Horus' plan to drive on Terra. Erebus had managed to complete his blasphemous ritual on Calth's surface, which summoned a Ruinstorm to the galaxy's Eastern Fringe -- a monstrous Warp Storm larger and more destructive than anything space-faring humanity had witnessed since the days of the Age of Strife. It would split the void asunder, dividing the galaxy in two and rendering vast tracts of the Imperium impassable for centuries.

The Ruinstorm would also isolate and trap those Loyalist forces caught behind it like the Ultramarines, preventing them from coordinating their efforts and supporting one another as the Traitor Legions moved towards Terra. It would even prevent them from warning each other, for a time, of the Warmaster's betrayal and the civil war that had begun to consume the Imperium. The Ruinstorm would leave Terra alone in the void, infinitely vulnerable to the approaching shadow of Horus.

Some of the warships destroyed during the Calth Atrocity would continue to circle the tortured Veridian star for over 100,000 years as frozen wrecks. They served as silent tombs for the dead, eternal funerary monuments to the greatest betrayal in human history.

The Ultramarines learned another hard lesson at Calth. The Calth Atrocity represented the Loyalist Astartes' first sustained experience with fighting the Warp entities later known as daemons in realspace. The Ultramarines realised that their decision to accept the anti-psyker dictates of the Council of Nikaea had lead to their voluntary surrender of the one weapon that might have proved most potent against the horrors of the Warp. It was almost as if the Traitors had known what was coming, and had orchestrated events so that the Imperium would voluntarily cast aside the only practical weapon it possessed against the sorceries of the Empyrean just before it was needed most. After the Ultramarines' experience at Calth, Roboute Guilliman sought to petition the Emperor for the revocation of the Edicts of Nikaea and the reinstatement of the corps of Librarians within all of the Loyalist Space Marine Legions. When the Horus Heresy ended and Roboute Guilliman initiated the Second Founding and the Reformation of the Imperium, he would get his wish, and the Imperium would once more make use of psychic powers against the Forces of Chaos despite the inherent dangers.

Though the XVII Legion had achieved a monumental victory of sorts, it was all a matter of perspective. Piercing the veil of the Warp, Lorgar had heard the whisperings of the Chaos Gods and had witnessed the truth for himself. Yes, Erebus had successfully conjured the Ruinstorm at Calth. But ultimately, Erebus and Kor Phaeron had failed to achieve their overall objectives: Roboute Guilliman was still alive, the Word Bearers had lost half the fleet at Calth to an Ultramarines counter-attack, and tens of thousands of Word Beaers, including the Gal Vorbak and mortal servants, had been abandoned to a useless subterranean war beneath Calth's irradiated surface while the two Word Bearers commanders had fled. This meant that the Word Bearers left behind were left to die, never to be reinforced. Never to be recovered. All those Gal Vorbak who had spent months of their lives fasting, praying, scarring their flesh in preparation for a chance to taste the Divine Blood, they had simply been lost for no real gain. Though Lorgar was somewhat displeased, Erebus had more or less achieved the base level of success required of him; the Ruinstorm had been conjured and the rogue elements of the Word Bearers had been culled. Now it was time for Lorgar to further his own plans and complete the campaign against the Ultramarines he had come to call his Shadow Crusade.

Shadow Crusade
Simulataneous with the Word Bearers' assault on Calth, Lorgar and the more reliable Word Bearers under his command launched a second offensive, a joint Shadow Crusade with his brother Angron and his World Eaters Legion into the rest of the Realm of Ultramar, laying waste to the Five Hundred Worlds with reckless abandon, slaughtering twenty-six worlds in rapid succession. This was to ensure the success of the sorcerous Ruinstorm, which would ultimately split the void asunder, dividing the galaxy in two and rendering vast tracts of the Imperium impassable for centuries, effectively cutting Ultramar off from the rest of the Imperium. This prodigious Warp Storm would deny needed reinforcements to the Loyalists as Horus drove on Terra in an attempt to overthrow the Emperor of Mankind. Nothing from Terra would get in and nothing would get out. Not even an astropathic whisper would be able to pierce this storm of Warp energy bleeding into realspace.

During this campaign of destruction, Lorgar had come to realise that over the course of their Shadow Crusade, Angron's temperament and mental stability had steadily grown worse. His cybernetic neural-implants known as the Butcher's Nails were killing him faster than Lorgar had originally imagined, faster than anyone realised. The rate of degeneration had accelerated very quickly in the months after the Battle of Calth. The implants had never been designed for the peculiar genetics of a Primarch's brain. Angron's physiology was trying to heal the damage produced by the implants as the Nails bit deeper. To save his life, Lorgar convinced the Lord of the World Eaters to go back to his homeworld of Nuceria. The overlords of the gladiatorial games on that world who had first hammered the foul device into Angron's skull would know more of the implant's function than the Traitor Legion's savants and the Dark Mechanicum. The two Primarchs would learn all that was known about the Nucerians' insidious cortical implant technology, and then they would burn that loathsome world until its surface was nothing but glass. Angron would finally take the vengeance he pretended to no longer desire. Whether Angron fought him, hated him or trusted him, mattered little to Lorgar, who intended to drag Angron into the immortality that he deserved before the Dark Gods whether he wanted it or not.

Guilliman's retribution fleet, which had been tracking the rest of the Word Bearers Legion in the wake of the Battle of Calth, finally caught up to the Traitors upon Angron's homeworld of Nuceria, which the World Eaters Legion were preoccupied with wiping clean of all life in vengeance for the treatment the Nucerians had merited out a century before to Angron. The XIII Legion warship Courage Above All, Guilliman's temporary flagship, broke Warp at the system’s edge, at the head of a large void armada consisting of 41 vessels. The Ultramarines armada looked wounded, cobbled together from separate fleets. It was not a dedicated interdiction war-fleet, but clearly a ragtag strike force, a lance thrust to the enemy’s heart. Guilliman himself had done the best he could with limited resources. The XIII Legion's Cruisers and Battleships ran abeam of the enemy fleet for repeated exchange of broadsides, offering targets too big and powerful to ignore, while the rest of the Ultramarines fleet used calculated Lance strikes from safer range. The armada then divided its assault potential, doing its utmost to destroy Lorgar's flagship Fidelitas Lex, and attempted to take the World Eaters' flagship Conqueror in a boarding action.

But the Ultramarines' warships not only fought a void war, they also attempted to take the fight to the surface of Nuceria, for this attack was personal. The Ultramarines had come for revenge against Lorgar and the Word Bearers, just as they had pursued Kor Phaeron all the way to the Maelstrom on the other side of Ultramar. Several Ultramarines warships attempted to make a run on Nuceria, haemorrhaging Drop Pods, landers and gunships, forcing planetfall by any means necessary. The Ultramarines fleet swept over and against the Traitors like an insect horde. But the tenacious commander of the Conqueror, Lotara Sarrin, put up a difficult fight and destroyed a number of Ultramarines vessels that attempted to make a run for the surface. Though the World Eaters' flagship transformed a number of the smaller vessels into flaming wreckage, the Ultramarines eventually punched through her tenacious defence and managed to land troops on the surface of Nuceria.

Meanwhile, the Fidelitas Lex was already a ruin, its armour pitted and cracked, its shields a memory. The cathedrals and spinal fortresses barnacling along its back were gone, laid waste by the Ultramarines’ incendiary rage. The XIII Legion's armada attacked in strafing runs and protracted exchanges of broadsides, trading fire with the superior warship and accepting their own casualties as the cost of bleeding the bigger vessel dry. Each assault left the Lex weaker, firing fewer turrets and cannons, taking punishment on its increasingly fragile armour. But she fought on. Crawling with smaller ships, the Lex lashed back with its remaining Macro-cannons, rolling in the light of its own burning hull. Guilliman guided the battle from the command deck of Courage Above All, and had decided that the Lex would die first, killed in the death of a thousand cuts and swept from the game board, while the Conqueror would be boarded and killed from within. In the course of the battle in Nucerian orbit, the Conqueror could not rise to its sister-ship’s defence. Both Traitor Legion flagships fought alone, starved of support and suffering the endless attacks of the XIII Legion’s ragged armada. Salvation Pods streamed from the Lex’s sides and underbelly, along with heavier Mechanicum craft and bulk landers. With the Legionaries of the Word Bearers already on the surface, the ship’s human population fled in the vessel’s final minutes. And still the great vessel fought -- rolling, turning, raging. The Ultramarines Cruisers that drifted past burned as badly as the warship they were killing. This void battle was a form of dirty fighting between warships, too close for the neat calculations of ranged battery fire. Instead, it was an up close and personal slugfest.

The Ultramarines Battle Barge Armsman intercepted the Conqueror and came abeam, launching Assault Carriers and Boarding Torpedoes. While the World Eaters flagship was busy repelling boarders, a number of smaller XIII Legion vessels slipped past her defences and launched Drop Pods, gunships and troop carriers. The first Drop Pods hammered home on the planet's surface. Sealed doors unlocked and the first Ultramarines poured forth, Bolters raised, moving in perfect and well-trained unity. But the World Eaters were waiting for them. Those not lost to the Butcher's Nails at once had the presence of mind to note that these Ultramarines weren not the pristine cobalt-blue warriors they had previously faced on the War World of Armatura. These Legionaries of the XIII wore cracked Power Armour, still scarred and burnwashed from some horrendous battle weeks or months before. These were hardened veterans of the Calth Atrocity. They burned with a cold intensity to carry out the vengeance in their hearts, and were intent on getting to grips with the Word Bearers.

As was their way, the Ultramarines established footholds at defensible positions, clearing room for their reinforcements to land. For every position they held, another was overrun by the World Eaters in a storm of roaring axes, or lost to the Word Bearers' chanting, implacable advance. The XII Legion crashed against the XIII in rabid packs, showing why Imperial forces had feared to fight alongside them for decades. Uncontrolled, unbound, unrestrained, they butchered their way through Ultramarines strongpoints, enslaved to the joy of battle because of the Butcher's Nails cortical implants sandwiched within the meat of their minds. The XVII Legion also met their Loyalist cousins, replacing ferocity with spite and hate. The Ultramarines returned it in kind, hungry for vengeance against the vile Traitors who had defiled Calth and damaged its star. Word Bearers units marched, droning black hymns and chanting sermons from the Book of Lorgar, bearing corpse-strewn icons of befouled metal and bleached bones above their regiments.

As the fighting raged, the burning shell of the Fidelitas Lex cut through the clouds into the planet's atmosphere, shuddering on its way east, rolling ever downwards, achingly slow for something of such scale. The weight of the Lex's massive plasma engines dragged the stern down first, colliding with the Nucerian ocean's surface far from shore. In the meantime, the demigod in gold and blue had finally found the object of his obsession amidst the clamour of war. Guilliman confronted Lorgar, possessing the advantage of two weapons, but Lorgar's Crozius gave him a reach his brother lacked. When they first met, there was no furious trading of frantic blows, nor were there any melodramatic speeches of vengeance avowed. The two Primarchs came together once, Power Fist against War Maul, and backed away from the resulting flare of repelling energy fields. Their warriors killed each other around them both, and neither Primarch spared their sons a glance. Lorgar flicked the clinging lightning from the head of his Crozius, shaking his head in slow denial.

Both Primarchs fought without heeding their warriors, their godlike movements an inconceivable blur to the Space Marines fighting around them. None had ever imagined the heroes of this new age would take the field against each other, nor could they have predicted the wellsprings of spite between them. Guilliman confronted Lorgar for what his Legion had done across the Five Hundred Worlds of Ultramar. In his righteous anger the Ultramarines Primarch struck Lorgar with one of his fists, battering the Word Bearers Primarch's sternum. Lorgar repulsed him with a projected burst of telekinesis, weak and wavering, but enough to send his brother staggering. The Crozius followed, its power field trailing lightning as Lorgar hammered it into the side of Guilliman’s head with the force of a cannonball. Both Primarchs faced each other beneath the grey sky, one bleeding internally, the other with half of his face lost to blood sheeting from a fractured skull.

As the two Primarchs were locked in their furious life-and-death struggle, they were oblivious to the destruction being wrought around them. Suddenly, Angron burst forth from the Ultramarines ranks, his armour a shattered wreck, and both of his Chainswords spat gobbets of ceramite armour plating and scarlet gore. Angron was plastered with the blood of the slain after hours in the crush of the front lines of intense combat. On his chest hung a bandolier of skulls taken from the mass grave at Desh’elika Ridge. Blood painted them as surely as it marked Angron. Even through the constant pain generated by the Butcher's Nails, that pleased him. He wanted his deceased brothers and sisters to taste blood once more. He had carried them with him across Nuceria, letting their empty eyes witness the razing of his former, hated homeworld. The World Eater launched himself at Guilliman with murderous hatred. The two Primarchs fell into a seamless, roaring duel where Lorgar and Guilliman had abandoned theirs. Guilliman found himself forced back by the storm of Angron's blows.

Once on Nuceria, Angron had paid his respects to his fallen brothers and sisters amongst the Nucerian gladiators he had once fought beside, whose bones now lay exposed to the elements on the Desh'elika Ridge where they had died. The painful memories of that day, long ago, were too much for the Primarch to bare. After paying a visit to the city-state of Desh'ea to see who ruled the Nucerian city-state that had once claimed to own him, he became enraged when he was told the tale of how he had fled at the Battle of Desh'elika Ridge, and the subsequent massacre of the rebel army in the mountains. The rebels had died to a man in his absence. Enraged by the lies that had been told about him over the last century, Angron ordered his Legion to kill everyone in the city. Then they were to kill everyone on the planet. At the height of the final battle against the last city on Nuceria, Lorgar was confronted by his wrathful brother Roboute Guilliman, who had been chasing him and the XII Legion since the destruction of Calth. As the two Primarchs fought, Guilliman gravely wounded Lorgar and was about to deliver a killing stroke to his wretched brother. But Angron had seen Guilliman's assault upon Lorgar and intervened, facing the Lord of Ultramar in single combat.

On Angron's chest hung a bandolier of skulls taken from the mass grave at Desh'elika Ridge. Blood painted them as surely as it marked Angron. Even through the haze of pain created by the Butcher's Nails, that pleased him. He wanted his former brothers and sisters, the Eaters of Cities, to taste blood once more. He had carried them with him across Nuceria, letting their empty eyes witness the razing of the high-rider cities. As the two Primarchs fought, Guilliman landed a glancing blow, his fist pounding across Angron's breastplate. One of the skulls of Angron's fallen kinsman that hung from the chain worn across his breastplate was partially shattered and scattered across the ground. Guilliman stepped back, his boot crushing a skull's remnants to powder. Angron saw it, and threw himself at his brother, his howl of wrath defying mortal origins, impossibly ripe in its anguish.

Lorgar saw it, too. The moment Guilliman's boot broke the skull, he felt the Warp boil behind the veil. The Bearer of the Word started chanting in a language never before spoken by any living being, his words in faultless harmony with Angron's cry of torment. Lorgar enacted his dark plan to save his brother's life, summoning the Ruinstorm to the world of Nuceria, tearing the sky open and unleashing a crimson torrent, formed from the ghosts of a hundred murdered worlds, raining blood. Lorgar focused his concentration on the triumphant form of his mutilated brother, calling for the Neverborn, the entities men called daemons, to answer in kind. He locked Angron’s muscles, setting fire to the synapses in his brain. The first spasms wracked their way through Angron’s sinews, turning his blood to quicksilver, then to lava and at last to holy fire. His cries of thwarted rage were tainted by an agony beyond comprehension. His body started tearing itself apart, growing, rising. Perfecting, after a lifetime of broken torture. This was the moment of Angron's apotheosis into daemonhood.

The World Eaters Librarians, those few who had never received the deadly Butcher's Nails implants which were inimicable to psykers, sensed the fey powers summoned by Lorgar from the Warp. In an attempt to halt the Urizen's dark plans, the 19 remaining Librarians harnessed their collective psychic powers to manifest a psychic entity known as the Communion, the gestalt consciousness of 19 psychic minds. In the midst of Lorgar's incantations, the Communion pulled the soul of the Primarch from his body. The two psychic entities confronted one another within the Warp, locked in a deadly contest of wills, each convinced that they were the one responsible for saving Angron. But ultimately, the Communion failed, for Lorgar was just as powerful in the Warp as he was in the material universe. After Angron's completed metamorphosis into a new Daemon Prince, the Daemon Primarch turned his attention to the Librarians. The creatures that had pained him for decades. The warriors that had made the Butcher's Nails sing and his brain bleed just for the sin of standing near them. Now they moved against his brother, hurling their foulness at Lorgar, who crouched one-handed and wounded, down on his knees. The Daemon Primarch's rage killed the remaining Libarians, each of them tasting a different doom. Angron killed the last of the Librarian, expunging his Legion of the weakness that had plagued his gene-sons since his reunification with them a century earlier. The Librarius of the World Eaters, the last fragment of the War Hounds within the XII Legion, was no more, a fact which greatly pleased the Blood God Khorne, who would not brook the existence of any psykers amongst his chosen servants. Lorgar had offered up the XII Legion to the whims of the Blood God as his loyal servants. Now there would only be blood, an ocean of blood carried on a tide of eternal slaughter.

The gravely wounded Guilliman escaped from Nuceria, unable to face or even fully comprehend what both of his brothers had become through their corruption by the Ruinous Powers. The World Eaters completed their purge of Nuceria until not one human life remained on the benighted world. Angron, now the very embodiment of the Blood God's Eight-Fold Path, shook the dust of the world from his feet and did not think of it again. Lorgar believed that he had "saved" his brother. In his mind it was the only way, for he alone had sought to save Angron from the implants that were killing him by degrees. Only Lorgar had found a way to free Angron from an existence of unrivalled agony, and he alone had acted to save his tormented brother. Now the Shadow Crusade could move on from Ultramar and rejoin Horus. The next target for the Traitors would be Terra itself.

Signus Campaign
When the Imperial Warmaster Horus, the greatest of the Emperor's genetic sons, fell to the temptations of the Chaos Gods and became swayed by their promises of power, he sought to sway his brother Primarchs to his cause. Horus and Sanguinius, the Primarch of the Blood Angels Legion, had fought many campaigns by each other's side. Their relationship was so close it had even incited jealousy amongst their brother Primarchs on occasion. But in his black heart Horus knew that Sanguinius would never willingly betray their father, and so he had formulated an audacious plan to either convert the Blood Angels Legion to his cause or utterly destroy them. To this end, Horus had discovered decades earlier a carefully guarded secret of the Blood Angels when he fought alongside Sanguinius' IX Legion in a xenocidal campaign on the world of Melchior. Horus had come upon his brother Primarch in a sunken ruin of an alien chapel and had witnessed the unthinkable -- Sanguinius murdering one of his own Astartes. Sanguinius explained his actions to his bewildered brother. He had discovered that within his own genome there was a trait that lay buried and waiting to be awakened. This genetic flaw would later be known as the Red Thirst.

Sanguinius had been aware of the flaw in his genome for several years, keeping the truth from the Emperor and his fellow Primarchs. Some of the Angel’s sons had learned a measure of the truth, but only Azkaellon, First Captain Raldoron, the IX Legion’s Master Apothecary on the Legion homeworld of Baal and a few others were fully aware of the extent of this affliction. They were united with Sanguinius in finding a way to repair this Flaw. Horus swore to his brother that he would never speak of this matter to anyone, even their father. He would keep this promise for as long as Sanguinius wished him to. The Angel was touched by his brother's gesture and expressed his gratitude. Horus solemnly vowed to help Sanguinius deal with this matter, however long it took. Little did they know at the time, that one day a corrupted Horus would take full advantage of this knowledge and attempt to turn the Blood Angels' Flaw against them.

Sanguinius Betrayed
Decades later, Horus exploited this knowledge of the Blood Angels' genetic Flaw. The Warmaster had found a way to sway his "beloved" brother's Legion to his cause and the service of the Chaos Gods. In his capacity as Imperial Warmaster, Horus ordered Sanguinus to gather his entire Legion and make for the Signus Cluster, a triple star system located in the Ultima Segmentum near the Eastern Fringe. His IX Legion was to cleanse the 7 worlds and 15 moons that comprised the Signus Cluster of xenos invaders and release the humans settled there from their xenos-overlords in what would later be known to history as the Signus Campaign. To further entice Sanguinius, the Warmaster informed him that he had found the means by which the Blood Angels would be able to excise the darkness from within their souls, and rid themselves of the Flaw. If Sanguinius obeyed the Warmaster's command in this matter, then Horus promised him that the Blood Angels would find a new freedom. Sanguinius had no reason to doubt Horus, for they were as close as two brothers could be. Many of their fellow Primarchs were even jealous of the closeness between the pair. Sanguinius relished the opportunity to once again prove the value of their bond, and so the Blood Angels Legion gathered in its entirety and duly set course for the Signus Cluster, unaware that they were heading into a terrible trap.

Unaware of the Warmaster's perfidy, Sanguinius willingly obeyed his brother Primarch and immediately set out for this volatile region of space. Unbeknownst to the Blood Angels, they were blindly walking into a deadly trap, for the Signus Cluster had fallen prey to agents of the Ruinous Powers and become a veritable Realm of Chaos -- a system of hellish Daemon Worlds under the rule of a Greater Daemon of Slaanesh known as Kyriss the Perverse. When the Blood Angels arrived in-system, their fleet was ambushed by the malevolent forces of the Warp, crippling or killing many of their Navigators and Astropaths in the initial onslaught. The Blood Angels now faced the fury of Chaos for the first time. Kyriss sent an image of himself to Sanguinius, declaring his lordship over the system in the name of Slaanesh and taunting the Primarch into taking it back from him. Though they had never faced such a foe, the Blood Angels prepared their counterattack, sure that they would prevail. Rising to the challenge of the vile Greater Daemon, the Blood Angels Legion attacked the daemon host of Kyriss, launching a series of attacks across the seat of the daemon's power, the world of Signus Prime.

The Black Rage
During the epic battle, Sanguinius came face-to-face with a new nightmare known as Ka'bandha, a Greater Daemon of Khorne. During the battle that ensued, Sanguinius was sorely wounded and temporarily incapacitated. He witnessed Ka'bandha slaughter 500 of his sons with huge swathes of his mighty axe. The psychic backlash of the deaths of so many of his sons blasted Sanguinius into unconsciousness. With the fall of their Primarch and the slaughtering of their brethren, the Blood Angels Legion was consumed by a black rage that drove them into a berserker's fury as they charged into the daemonic horde and in their madness they smashed the horde of daemons asunder. Yet the brutal violence of the daemon Ka'Bahnda had unleashed something dark within the psyche of the Space Marines, a thirst for blood that would not be slaked until every taint of Chaos had been erased from the planet. Even the mighty Kyriss was banished back to the Immaterium. Only when the planet was cleansed did the rage of the Blood Angels finally subside. Though Signus had been freed from its thrall to the Forces of Chaos, the cost of victory was far higher than any could have wished. The berserker rage the Blood Angels had experienced had left a brooding shadow on their souls that would manifest in the centuries to come as the great curse (later known as the Black Rage) that would afflict the Blood Angels and their later Successors.

Fall of the Iron Warriors
As the tragic outbreak of the Horus Heresy had grown closer, it appeared that Perturabo, Primarch of the Iron Warriors Legion, had become ever more bitter over the fact that his Legion had often been used for ginding siege duties that resulted in little glory or recognition. Events eventually came to a head when, leading his Iron Warriors on a campaign to cleanse the Hrud Warrens on the world of Gugann, the Primarch received news that his own homeworld, Olympia, had risen up in rebellion against the Imperium. The Olympian demagogues had brought the people together and risen in arms against the rule of the Emperor of Mankind. The thought of being the only Primarch who could not control his own Legion's homeworld appalled Perturabo.

Perturabo and the IV Legion returned to their homeworld and brutally purged Olympia of its rebels city by city, overrunning the fortresses he had built and sparing no one who stood against him. By the time the massacre was over, five million Olympians had been killed and the rest put into vicious slavery to the Iron Warriors. Perturabo looked on at the remains of his homeworld in cold silence. Only once the great pyres were burning to cleanse the world of the heaps of corpses created by the IV Legion's assault did Perturabo fully realise what he had done. The Iron Warriors were no longer the saviours of the Imperium; they had been destroying the alien Hrud one moment and yet, in the next, they were committing genocide against their own people. With the cooling of Olympia’s mass funeral pyres had come the realisation that nothing the Lord of Iron could ever do from that moment could ever atone for a worldwide genocide. His father would never forgive him so grievous a sin, but Horus had not only forgiven it, he had lauded his brother’s thoroughness and dedication. Horus had sworn Perturabo never to feel guilt over what he had done to Olympia, but that was an oath easier to make than to live by.

It was at this time that disturbing news of the outbreak of the Horus Heresy on the world of Istvaan III reached Olympia and new orders for the Iron Warriors came from Terra. Leman Russ and the Space Wolves had attacked Magnus the Red and his Thousand Sons Legion on their homeworld of Prospero at the direction of the Emperor and as a result of the deceit of Horus. Horus had turned Traitor with his XVI Legion, the Sons of Horus, alongside some other allied Legions such as the Death Guard, Emperor's Children and the World Eaters. The whole of the Imperium was on the brink of an outright civil war. The new orders from the Emperor ordered the Iron Warriors to join with six other Loyalist Space Marine Legions to face Horus and his Traitor Legions on the world of Istvaan V. During the battle that followed the Iron Warriors, Night Lords, Word Bearers and Alpha Legion all went over to the side of Horus and almost completely destroyed the three remaining Loyalist Legions of the Imperial assault force -- the Iron Hands, the Salamanders and the Raven Guard -- at the infamous Drop Site Massacre on that world. In truth, Perturabo and the other Primarchs who turned Traitor on Istvaan V had already been seduced by the Warmaster and made their decision to stand with him against the Emperor, guaranteeing that the Traitors would field nine Space Marine Legions against the Loyalists.

Hydra Cordatus
As Horus’ rebellion ground on, the Iron Warriors took the time to humble their great enemies, the Imperial Fists, upon the isolated world of Hydra Cordatus that the Sons of Dorn had recently brought into Imperial Compliance. The Iron Warriors made planetfall in the wake of a saturation bombardment that reduced the valley where the planet's lone formidable fortress, known as the Cadmean Citadel, was situated and the agri-settlements filling its fertile deltas to ash. Magma bombs and mass drivers boiled away the rivers and reduced fecund earth to arid dust. The Cadmean Citadel was left untouched, and the small garrison of Imperial Fists Legionaries that Rogal Dorn had left behind still found it difficult to believe that such a precise bombardment was possible. But the Iron Warriors had purposely done this in order to show the Imperial Fists that they were superior to them in every way. The technological cunning of the ancient fortress builders, married to the artfully wrought geography and the courage of the defenders, proceeded to keep the Iron Warriors at bay for almost three months. Every day the Loyalist warriors stayed alive, it kept the enemy from redeploying and bringing their strength to bear elsewhere against the forces of the Imperium. Yet, when the Iron Warriors finally overcame the citadel’s ancient defences and broke open its walls they ran amok. They slaughtered the remaining Imperial Fists Legionaries, the heroic men and women of Hyrdra Cordatus that had chosen to stand with them, and the refugees from the devastated fields below the fortress. Fifty-two Imperial Fists and thirteen thousand men, women and children were crammed within the citadel’s walls. When the final assault came, the Lord of Iron himself spearheaded the audacious attack upon the citadel's defenders, and slaughtered over thirty Imperial Fists Astartes in a span of only a few minutes. The rest of the Cadmean Citadel's defenders were slaughtered to a man and the surviving mortal refugees were enslaved by the Iron Warriors before they moved on to their next objective. Hydra Cordatus was reduced to a barren desert world by the Traitor Legion's assault.

Angel Exterminatus
Following the Iron Warriors' victory on the world of Hydra Cordatus, word reached the Lord of Iron that Fulgrim, Primarch of the Emperor's Children Legion, wished to rendezvous with him to discuss something of great import. Though the Phoenecian had yet to reveal the true purpose of his visit, he had promised Perturabo that it was "wondrous." Perturabo knew that his brother had a flair for the melodramatic, which only seemed to have gotten worse since the III Legion threw their lot in with the Warmaster. The Lord of Iron counted none of his fellow Primarchs as close, but the Phoenician’s adherence to perfection in all things had once provided common ground between the two superhuman warriors and allowed them to talk as trusted comrades-in-arms if not beloved brothers. What the Emperor’s Children had sought with constant movement towards the attainment of perfection, the Iron Warriors earned with rigid discipline and methodical planning; two divergent paths to the same ultimate goal.

Perturabo believed Fulgrim's visit had something to do with Mars. The Warmaster needed the Martian theatre fully secured before they moved against Terra, and he believed that Fulgrim was there to seek the Iron Warriors' aid in breaking open the forge-cities of the Mechanicum. If he was right, Perturabo wanted his Legion to have a plan in place to achieve that objective. Until the Iron Warriors received further orders, Perturabo would humour his brother and listen to what Fulgrim had to say. While making plans for the upcoming campaign, Perturabo received word that the Emperor's Children had arrived, unannounced, on the surface of Hydra Cordatus. Over three hundred drop-craft had landed beyond the mouth of the valley where the Iron Warriors had made their encampment.

The IV Legion quickly gathered in formation to honour the III Legion with a vanguard to receive them. Battalions of Thorakitai Imperial Army troops stood ranked in their tens of thousands. Before them stood two hundred Grand Battalions of Iron Warriors, fifty thousand warriors in amberdust-burnished warplate. Such a display of might and magnificence had not been seen since the slaughter unleashed upon the black sands of Istvaan V. Yet Perturabo and his senior officers looked on in awe at the gaudy cavalcade of noise, colour and spectacle that emerged from the III Legion's drop site into the valley. Fulgrim and his Emperor’s Children were now completely unrecognisable from the honourable warriors that had once formed the III Legion. Perturabo knew something fundamental had changed within the Emperor’s Children, but could not imagine what purpose the disfigurements and degradations its warriors now sported could possibly serve.

Fulgrim met with his brother Primarch in the private inner sanctum of his command bunker with an enticing offer that Perturabo could not refuse; the means to make it so that the Lord of Iron's every desire could be made real and would never disappoint, never fail to live up to his fondest expectations, and never, ever be eclipsed. Fulgrim came with an offer to unite their mutual forces in battle on a glorious quest. One that might tip the balance of the Warmaster’s rebellion. Though Perturabo was suspicious of his brother's intentions, perhaps this joint venture would grant understanding through common cause. Fulgrim revealed his purpose; they were to venture to the Warp Storm that had plagued Perturabo's dreams all of his life. Within it was hidden an ancient and forbidden xenos weapon known as the Angel Exterminatus. It had been hidden in the grave of its doom, a weapon of such power that the stars themselves turned upon it rather than allow it to escape its prison.

Into the Eye of Terror
"A name to lodge in the hearts of all who hear it."

- Primarch Perturabo, after permanently coining the name for the Eye of Terror on the stellar astropathic charts.

For as long as he remembered, no matter how many thousands of light years separated him from this particular Warp Storm, Perturabo was always aware of the Eye of Terror's presence and could perceive an echo of it on every world where he had looked to the heavens. He did not know whether this Warp sight had been engineered into his perceptive apparatus deliberately, like Sanguinius’s wings or Corax’s eyes, or was simply a quirk of his genetic code, but it had been a blessing and a curse since his earliest memories. The anomaly haunted his dreams, threaded his nightmares and coloured his every thought since he had learned something of its nature. He had once asked the Iron Hands Primarch Ferrus Manus whether his silver eyes allowed similar insight, but his brother had just shaken his head and given him a look of faint scorn, as though he had just admitted to some secret weakness or vice. He had never mentioned it again.

When the joint fleet of the III and IV Legions arrived at the outskirts of the stellar maelstrom, for once in his life, Perturabo looked upon it and knew that others could see it too. They did not see it quite as he saw it, but they could at least acknowledge its existence. He saw beyond its dark light to the engulfed worlds within: phantom images that ghosted in and out of perception and fleeting moments of solidity in a realm where such things were anathema. He saw planets where all reason and Euclidian certainty had been abandoned, where the physical laws that underpinned the galaxy were playthings of lunatic forces beyond mortal comprehension. And now he was to venture into its depths, following the guidance of an alien seer.

Before entering the Warp Rift, Perturabo called up the astrogation charts of this region of space, reading the flickering labels of the charts' keys for those few stellar objects in this region worthy of a name. At the heart of the hologram, a vertical black label bisected the fiery orange heart of the Warp Storm. Imposed upon the bar was the name Cygnus X-1. Perturabo knew the Warp Storm was not the first spatial anomaly to bear that name, and whichever lowly scribe had scribed it again was a fool. Something this powerful and terrible deserved a name to strike fear into the hearts of all who saw it, a name that would resonate down the millennia until the end of time, when the stars went out and the only light in the universe was the nightmare glow of the maelstrom’s ever-devouring borders. Perturabo’s fingers danced over the slate from which the charts had been brought forth, and the name in the vertical black bar changed. It would change throughout the Traitor Legions' fleets, spreading to any data engine that called up maps of the galactic northwest. It was a name to lodge in the hearts of all who heard it and would eventually be adopted by the forces of the Imperium as well -- The Eye of Terror.

Sisypheum
Unknown to both the Iron Warriors and the Emperor's Children, they were being pursued by a ragtag group of Loyalist Astartes who were survivors of the Drop Site Massacre of Istvaan V and were determined to stop the Traitors at all costs. These Loyalist Space Marines were gathered from survivors that had fought their way out of the killing ground of the Urgall Depression on Istvaan V. They had managed to escape the Istvaan System aboard an Iron Hands Strike Cruiser known as the Sisypheum. Iron Hands Astartes and their mortal serfs formed the bulk of the warship's crew, but surviving warriors of the Salamanders and a single Raven Guard Astartes were also counted among their number. In the wake of the slaughter, escape from the Istvaan System had been a nerve shredding series of mad dashes under fire and silent runs through the Traitors' orbital blockade, culminating in a final sprint to the gravipause, the minimum safe distance between a star’s mass and a vessel’s ability to survive a Warp Jump. The Sisypheum had escaped the trap, but not without great cost.

The months that followed saw the Sisypheum embark on a series of hit-and-run attacks on Traitor forces on the northern frontiers of the galaxy, wreaking harm like a lone predator swimming in a dark ocean. Traitor forces seeking flanking routes through the Segmentum Obscurus were their prey; scout craft, cartographae ships, slow-moving supply hulks heavily laden with mortal troops, ammunition and weapons. Disruption and harassment were the Sisypheum's main objective until contact had been established with disparate groups of Loyalist forces that had also escaped the massacre, and a stratagem of sorts agreed upon. With the X Legion too scattered to function in a traditional battlefield role, its surviving commanders found their own way to fight back: as the thorns in the flanks of the leviathan that distract it from the swordthrust to the vitals.

At Cavor Sarta, an Iron Hand known as Sabak Wayland and the lone Raven Guard survivor Nykona Sharrowkyn had captured an Unlingual Cipher Host -- one of the so-called "Kryptos" -- a hybrid abomination creature of the Dark Mechanicum that had previously made the Traitors' code network a cryptographic impossibility to break. With the Kryptos, Loyalist commanders were able to finally access the Traitors’ coded communications. And with this knowledge, the Sisypheum's Captain, the Iron Hand Ulrach Branthan, had ordered the Sisypheum to make the circuitous journey to Hydra Cordatus and the meeting of the Traitor Primarchs that had been indicated by the cracked communications. After learning of Fulgrim's intentions to enter the Eye of Terror and recover the Angel Exterminatus, the crew of the Sisypheum made their way towards the Warp Rift, aided by a mysterious Eldar guide with the intention of thwarting the Traitors' plan to acquire the unknown xenos weapon.

Crone World
The destination of the joint fleet of Iron Warriors and Emperor's Children vessels was the lost Eldar world of Iydris, a world said to have been favoured by the goddess Lileath. Iydris was one of the legendary Crone Worlds, which once formed the heart of the lost Eldar empire before they were consumed by the creation of the vast Warp Rift that was the Eye of Terror following the birth of the Chaos God Slaanesh. The lost world was located at the heart of the Eye of Terror, somehow remaining in a fixed position keeping it from destruction in the gravitational hellstorm of a supermassive black hole that lay at the centre of the eternal Warp Storm. It was from this epicentre that the galaxy vomited unnatural matter into the void, a dark doorway to an unknowable destination and an unimaginably powerful singularity whose gravity was so strong that it consumed light, matter, space and time in its destructive core.

Their ultimate goal was within the Primarchs' grasp; the Sepulchre of Isha's Doom, which sat at the centre of the citadel of Amon ny-shak Kaelis. The citadel stood astride the entrance to the prison tomb of the Angel Exterminatus. Before launching a full planetary assault, the Iron Warriors launched a preliminary orbital bombardment around the citadel, a standard practise when preparing to assault a potentially hostile environment. A cone of fire gouged the surface of Iydris, burning, pounding and flattening in the blink of an eye structures that had stood inviolate for tens of thousands of Terran years. A barren ring of pulverised earth encircled the citadel of Amon ny-shak Kaelis, leaving its walls, towers and temples an isolated island cut off from the rest of the planet’s structures by a billowing firestorm of planet-cracking force. In the wake of this orbital bombardment flocks of Thunderhawks, Stormbirds, Warhawks and heavy planetary landers launched from crammed embarkation decks. Bulk tenders descended to low orbit and disgorged thousands of troop carriers, armour lifters and supply barques. Titanic, gravity-cushioned mass-landers moved with majestic slowness as two Titans of the Legio Mortis took to the field, and this was but the first wave of the invasion. Another eight would follow before the martial power of two entire Space Marine Legions and their auxiliary Imperial Army forces had made planetfall.

Battle of Iydris
The Traitors' assault began five hours later, despite the full circuit of fortifications still being incomplete. The landing zone was almost surrounded, but the encircling walls had yet to meet one another. Layered rings of minefields and acres of razorwire spread from the outer faces of the walls, making the approach next to impossible for anyone without detailed maps and temporary dormancy codes. Leaving Warsmith Toramino and five thousand Iron Warriors to oversee the completion of the siege works and establish battery positions for the guns of the IV Legion's Stor-bezashk, Perturabo climbed to the cupola of his converted Shadowsword super-heavy tank, the Tormentor. The Iron Warriors had come in force and the Emperor's Children no less so. Like Perturabo, Fulgrim rode at the head of his army, a warrior god in impossibly bright armour. His brother might have ceded control of this mission to him, but Fulgrim was making sure he was still its figurehead.

For all intents and purposes, the route into the citadel of Amon ny-shak Kaelis was undefended and their route unopposed. Ever mistrustful of the lack of defences, Perturabo had his Iron Warriors dug in, assuming a perfect formation outside the walls in a layered barbican that protected the Traitor Legions' line of retreat. Fulgrim’s host broke apart into individual warbands, ranging in size from around a hundred warriors to groups of nearly a thousand. Each of these autonomous groups appeared to be led by a captain, though such was the bizarre ornamentation and embellishment on each warrior’s armour, it was often impossible to discern specific rankings. Leaving the fortified bridgehead behind, Perturabo led his Iron Warriors and the Emperor’s Children contingent into the heart of Amon ny-shak Kaelis. The Sepulchre of Isha’s Doom was a monumental palace, sprawling and richly ornamented with bulbous mourn-towers and sweeping, ivory-roofed domes. As the column of Traitors pressed onwards towards the sepulchre, they were being silently and unknowingly observed by the Loyalist Astartes of the Sisypheum. Despite being outnumbered a thousand to one, the small force of Loyalist Legionaries devised a means to find another way into the massive sepulchre.

As the two Primarchs neared their ultimate goal, Fulgrim kept pressing his stern brother with curt impatience to not linger. Perturabo took the time to study Fulgrim and his assembled host. His brother was sheened in sweat, but it was not perspiration that beaded his brow, Fulgrim was sweating light. Though it was faint, it was visible to Perturabo's gene-enhanced sight that saw beyond what even Astartes eyes were capable of detecting. He wondered if Fulgrim was aware of the radiance bleeding from him and decided he must be. His brother’s armour strained against his body and his features were drawn and tired, as though only by an effort of will was he still standing. His captains looked no better, like hounds straining at the leash. A number of Fulgrim's Lord Commanders' flesh was also suffused with a light similar to that enveloping Fulgrim, a deathly radiance that had no place within a living being. Perturabo did not trust Fulgrim one bit, knowing that inevitably he would be betrayed by his brother. The Lord of Iron pressed on, intent on bringing their quest to completion. As they neared their final destination at the heart of the sepulchre, the power at the heart of Iydris spasmed in hateful recognition of the followers of Slaanesh, known to the Eldar as She Who Thirsts, and awoke its guardians from their slumber.

Thousands of crystalline statues threw off their previous immobility. They moved stiffly, like sleepers awoken from an aeons-long slumber, and the gems at the heart of their bulbous heads bled vibrant colour into glassy bodies that suddenly seemed significantly less fragile. This army of wraiths were the Eldar dead of Iydris. Soon both the Traitor forces outside the citadel as well as those inside were attacked from all sides by the revenant army. Like automata, but with a hideously organic feel to their movements, the Eldar constructs emerged in their thousands with every passing second. As Perturabo was busy fighting for his life, Fulgrim slipped away in the midst of the fighting. Realising where he had gone, the Lord of Iron stepped into the green glow emanating from the centre of the massive chamber. Perturabo understood that this was no elemental energy or mechanically generated motive force, but the distilled essence of all those who had died there.

Perturabo descended downwards on an unending spiral towards a point of light that grew no brighter no matter how far he descended. The journey downwards was never-ending, or so it seemed until it ended. Fulgrim stood at the origin of a slender bridge that arched out to the centre of a spherical chamber of         incredible, sanity-defying proportions. The footings of the bridge were anchored on the equator, and a score of other bridges reached out to where a seething ball of numinous jade light blazed like a miniature sun. Iydris, it transpired, was a hollow world, its core this colossal void with the impossibly bright sun at its heart. Perturabo confronted his brother, realising that there was never an Angel Exterminatus. Fulgrim confirmed for Perturabo that there was no such weapon yet, for he was to be the Angel Exterminatus. Perturabo responded that his brother always did have an appetite for rampant narcissism, but this was the grandest delusion yet. Unamused at Fulgrim's explanation, Perturabo took a step towards his brother, Forgebreaker in his hand, intent on killing him. Fulgrim spoke a single word, its nightmare syllables tore at Perturabo's brain, causing him to stumble and drop to one knee. Fulgrim revealed the reason for his brother being drained of energy.

When Fulgrim had arrived on Hydra Cordatus he had presented the Lord of Iron with a gift; a folded cloak of softest ermine, trimmed with foxbat fur and embroidered with an endlessly repeating pattern of spirals in the golden proportion. A flattened skull of chromed steel acted as the fastener. Set in the skull’s forehead was a gemstone the size of a fist, black and veined with hair-fine threads of gold. As they had made their way towards the heart of the Eye of Terror, the large gemstone at the centre of the skull-carved cloak pin had changed from black to a solid gold colour and pulsed with its own internal heartbeat. This was the maugetar stone, known as the harvester, which had slowly been draining Perturabo's strength and life force. With the Lord of Iron's sacrifice, Fulgrim would finally be able to achieve apotheosis. The two Primarchs ascended upwards within the shaft of light, emerging into the chaos that was happening within the heart of the sepulchre.

Apotheosis of Fulgrim
The Primarch of the Emperor’s Children hurled his brother aside, and Perturabo fell in a languid arc to land with a crunch of metal and crystal at the edge of the shaft. Blood trailed the air in a streaming red arc from Perturabo’s chest. The Lord of Iron lay unmoving, his body broken and lifeless. The attention of every Astartes within the chamber was irrevocably drawn towards the Primarch, for they recognised that an event of great moment was in the offing. The Phoenician was no longer the same being as had descended into the planet. He floated in the air above the shaft, which no longer poured its green torrent up to the restless darkness above, but simply radiated a fading glow of dying light. Fulgrim’s armour was shimmering with vitality, as though the light of a thousand suns were contained within him and strained to break free. The Primarch’s dark, doll-like eyes were twin black holes, doorways to heights of experience and sensation the likes of which could only be dreamed by madmen and those willing to go to any lengths to taste them.

Just as Fulgrim was about to achieve his ultimate desire, Perturabo had regained enough of his former strength and rose to his feet, the maugetar stone in his hand. Perturabo walked towards Fulgrim, keeping the hand holding the maugetar stone extended over the shaft in the center of the chamber. Perturabo looked his brother in the eye for some hint of remorse, a sign that he regretted that things had come to this, something to show he felt even a moment of shame at plotting to murder his brother. He saw nothing, and his heart broke to know that the Fulgrim he had known long ago was gone, never to return. He had not thought it possible that anyone could plunge so far as to be beyond redemption. Perturabo knew that Fulgrim no longer wanted to be an angel, he wanted to be a god. He informed the Phoenician that Mankind had outgrown such beings a long time ago. Disgusted by Fulgrim's desires, Perturabo hurled the maugetar stone into the deep shaft.

Suddenly, a barrage of Bolter fire erupted and a handful of Emperor's Children Astartes were pitched from their feet. Black-armoured Space Marines bearing a mailed fist upon their shoulder guards charged towards the Traitors. It was the Astartes of the X Legion -- the Iron Hands. Soon the battle was joined, as Loyalist fought Traitor within the expansive chamber. The noose of battle was closing on the two Primarchs at its centre -- Perturabo locked on his knees, and Fulgrim hovering in the air as though bound to his brother by ties not even the call of war could break. The Iron Hands were mired in battle with the Emperor’s Children and Iron Warriors, zipping streams of fire blasting back and forth between them. During the battle, one of the Loyalist Astartes, the Raven Guard named Sharrowkyn, had acquired the fallen maugetar stone. He instinctively knew that if this stone was desired by Fulgrim, then it had to be destroyed. Taking a Bolter from a fallen Emperor's Children Astartes, he aimed the muzzle at the strange gold and black stone and pulled the trigger.

The weakened Perturabo was renewed with the sudden release of his lifeforce from the Chaotic relic. Fulgrim’s body arched in sympathetic resonance, for the maugetar stone contained more than just the strength stolen from Perturabo by Fulgrim. It contained their mingled essences, a power greater than the sum of its parts, a power to fuel an ascent so brutal that only the combined life-force of two Primarchs could achieve it. Armour burned from Fulgrim’s body, flaking away like golden dust in a hurricane, leaving his monstrously swollen body naked and his flesh blazing with furnace heat. Spectral flames of shimmering pink and purple licked around his body, a hungry fire waiting to consume him the moment his focus slipped. As the Lord of Iron finally pushed himself upright and stood fully erect, he lifted Forgebreaker onto his shoulder. Fulgrim saw his death in Perturabo's eyes and grinned, knowing that his brother had to do it. Perturabo hefted Forgebreaker like a headsman at an execution and swung the mighty hammer in a wide arc, splitting the Phoenician's body wide open. It was done. Fulgrim’s body exploded under the impact of Perturabo’s warhammer, and the cry of release was a shrieking birth scream. An explosion of pure force ripped from the Phoenician’s destroyed flesh, filling the chamber of towers with a blinding light that was too bright to look upon, too radiant to ignore. Like a newborn sun, the wondrous incandescence was the centre of all things, a rebirth in fire, new flesh crafted from the ashes of the old. Every eye in the chamber was turned to the light, though it would surely blind them or drive them to madness. Through slitted fingers and shimmering reflections, the survivors of the fighting bore witness to something magnificent and terrible, an agonising death and violent birth combined. A figure floated in the midst of the light, and it took a moment for Perturabo to recognise the impossibility of what he was seeing. It was Fulgrim, naked and pristine, his body unsullied by any of the mawkish ornamentations with which he had defaced his flesh, as perfect as the day the Emperor had first conceived him. Fulgrim’s back arched and his bones split with gunshot cracks. His flesh, once so perfect, now ran fluid and malleable, his form moulding and remoulding as though an invisible sculptor pressed and worked him like clay upon a wheel. Fulgrim’s legs, extended like the man of Vitruvius, ran and lengthened, fusing together in a writhing serpent’s tail, the skin thickening and sheening with reptilian scales and segmented plates of chitinous armour. Perturabo took a step towards this thing being born from the death of his brother, all the while despairing that this was his brother.

Perturabo had destroyed Fulgrim’s mortal shell. This was an immaterial avatar of light and energy, of soul and desire. What was being done here was an act of will, a creature birthing itself through its own desire to exist. Fulgrim’s face was a mask of agonised rapture, a pain endured for the pleasure it promised. Two obsidian horns erupted from Fulgrim’s brow, curling back over his skull, leaving his perfect face as unsullied as the most innocent child. Fulgrim ascended into Chaos, a prince of the Neverborn, a lord of the Ruinous Powers, the chosen and beloved Champion of Slaanesh. As the newborn Daemon Prince departed, the first of the Traitor Primarchs to achieve daemonic apotheosis, he left his brother with a cryptic message that they would one day meet again, and both brothers would yet renew their bonds. Lifting his hands into the air, a curtain of light rose up from the ground and Fulgrim and all of his Emperor's Children Chaos Space Marines disappeared in a flare of arcane teleportation energy.

With the disappearance of the Emperor's Children, the Crone World of Iydris began to tear itself apart. The force at the heart of the world was no more. The strength of the lifeforces of the dead Eldar that had kept it safe was failing, and soon this planet would be swallowed by the unimaginable force of the supermassive black hole that lay at the heart of the Eye of Terror. Across the chasm, the remaining Iron Hands gathered up their wounded and fell back from the spreading fissures and heaving ruptures opening in the floor. They looked upon Perturabo with hatred, but decided to make their way off-world from the doomed planet. They knew that they could not fight the Lord of Iron and live through the encounter. Perturabo let the Iron Hands depart. Then he led his warriors out of the crumbling citadel. Once aboard his flagship the Iron Blood, Perturabo watched the final death throes of the Eldar Crone World.

The Iron Blood strained to break orbit, but the force at the heart of the Eye of Terror was reasserting its grip on reality with a vengeance. Many of the smaller vessels of the Iron Warriors survivor fleet that had followed the Sisypheum had already been dragged within its embrace, swallowed by the black hole’s powerful energies. Only the capital ships had engines large enough to resist the inexorable pull, but even they were only delaying the inevitable. Perturabo's Triarchs stood patiently around their lord, awaiting his orders. The Lord of Iron informed them that he always moved forward, never backwards. They would go into the black hole. Though his senior commanders believed that it was suicide, the Lord of Iron informed them that Fulgrim had promised that the two brothers would meet again. The Iron Warriors were not meant to die within the Eye, and there was only one way onwards. His men moved to carry out his order, and the Iron Warriors fleet plunged deep into the heart of Terror.

Route to Terra
"Vengeance it is said is the preserve of the gods; gods we in our folly denied ever existed."

- Captain-General Orson Souzerin III, Solar Auxilia, introit to The Last Cohort

After the Drop Site Massacre, it became clear that 9 of the 18 Space Marine Legions had turned to Chaos and against the Emperor of Mankind. Horus openly and publicly declared that he would no longer follow the Emperor, believing Him to be undeserving of the battles fought in His name, and the Warmaster took over the formal leadership of the so-called Traitor Legions as their new overlord. Horus' Traitor Legion forces were supported and supplemented by elements of the Imperial Army willing or forced to follow Horus and his Legions, a portion of the Mechanicum and the Titan Legions corrupted by Chaos that were known as the Dark Mechanicus, strong Imperial naval forces then still part of the Space Marine Legions' Great Crusade Expeditionary Fleets, and the daemon-spawn of Chaos.

Over the next seven Terran years, the combined Traitor fleets spread across the galaxy, unleashing a brutal civil war upon many of the planets that they had once helped to bring into the Imperium. Secretly guided by the Ruinous Powers, the Traitor Legions and their related support forces no longer worried about the rules of war, civilian casualties or proportionality; it was a common tactic of the Traitor fleets to simply unleash a total orbital thermonuclear bombardment upon a single inhabited world in a heavily defended Imperial star system to induce all of the other worlds and orbital installations to surrender. Casual brutality and even genocide became the norm for the Traitors as they fell ever more deeply under the control of Chaos. Slowly but methodically, Horus and the Traitor Legions forged a path across the galaxy lit by the burning nuclear pyres of countless worlds. Those planets spared the destruction faced an even worse fate: occupation and control by the Chaos-corrupted Traitor forces, who took great pleasure in unleashing the perversions of the Dark Powers upon the captive populaces. Many prayed to the Emperor for release from their torments, and the strength of the Lectitio Divinitatus cult that believed in the Emperor's divinity only began to grow as the nightmare of civil war scourged the Imperium of Man.

Schism of Mars
It is not entirely clear how Horus managed to turn such a significant percentage of the armies under his command against the Emperor, but he was known to be a very skilled and persuasive leader who commanded immense personal loyalty amongst his subordinates. But even before the opening stages of his planned insurrection occurred, he knew he would have to secure the support of the Adeptus Mechanicus and their superior technology and weapons if he was to defeat the Emperor and conquer the galaxy. Horus won over the loyalty of many of the Mechanicus' Tech-Adepts after promising them the lost secrets of ancient Standard Template Construct (STC) technology that had been recovered from the worlds of the recently subjugated Auretian Technocracy by the Sons of Horus Legion.

The Heresy also struck at the technological and industrial heart of the Imperium on the Forge World of Mars, the sacred homeworld of the Mechanicum. The climate on Mars was full of discontent during this tumultuous time. There were tense relations between the various Techno-Magi with sporadic outbreaks of espionage and violence being committed against the various forges that represented the primary sociopolitical units of Mars. There were even unconfirmed suspicions that the Titan Legions had already secretly chosen sides in case of a potential conflict. Regulus, the Adeptus Mechanicus' representative to the Warmaster Horus who had already thrown in his lot with the Warmaster, was sent to Mars to secure the tentative support of the Fabricator-General of Mars, Kelbor-Hal. Regulus convinced the Fabricator-General of Horus' resolve to support increased autonomy for the Mechanicum under his rule rather than maintaining the more autocratic mandates of the Emperor that prevented the Mechanicum from doing exactly as it pleased. As a show of his appreciation for the Fabricator-General's support, Horus provided information to Kelbor-Hal that allowed the Mechanicum to open a repository of forbidden knowledge known as the Vaults of Moravec, which had been sealed for a thousand years. The Emperor Himself had decreed that the vaults never be opened, for they contained innumerable artefacts of technology that had been fashioned or corrupted by the malign power of Chaos. But the deal was struck,and the Fabricator-General accepted Horus' proposal and joined forces with the Warmaster, assisting the Traitors with all of the technology of Mankind at his disposal.

When this repository was reopened, there was all manner of forbidden arcane knowledge and weaponry that had obviously been tainted by the corrupting influence of Chaos stored within. Soon the corruption spread throughout the forges and temples across the Red Planet as scrap code -- Chaos-contaminated digital source code that was infected with an arcane computer virus -- infested the logi-stacks and Cogitator (computer) archives of the Adeptus Mechanicus, causing literal Chaos to emerge in any Cogitator system that was networked to one of its infected counterparts. The Fabricator-General and his Dark Mechanicum allies used this disruption to marshal the strength of their forces, intent on bringing the rule of Mars firmly under their control. Many Mechanicus forces that remained loyal to the Emperor as the embodiment of the Omnissiah were forced off-line or destroyed outright by the traitorous Fabriactor-General's ploy. In later years, the night the Chaos code was released would become known in Mechanicum legends as the Death of Innocence.

Open warfare erupted on the Red Planet in the wake of the Death of Innocence as Martian forces, both civilian and military, fought one another in a deadly civil war that mirrored the larger conflict consuming the Imperium. This internecine conflict became known as the Schism of Mars. Across the galaxy, open rebellion erupted as Space Marine Legion fought Space Marine Legion and Titans battled Titans. The members of what became known as the Dark Mechanicus supported Horus throughout the Horus Heresy and used dark and forbidden knowledge revealed by the Ruinous Powers to help destroy the Loyalist forces.

Fortifying Terra
As the years of conflict across the galaxy passed, the ultimate aim of the Traitor Legions' destructive interstellar advance soon became clear: their goal was the conquest of Terra, the heart of the Imperium. With this conquest, Horus could fulfill his promise to the Chaos Gods and throw down the Emperor of Mankind, their greatest enemy. The Sons of Horus, the Death Guard, the Emperor's Children, the World Eaters, and elements of the Word Bearers prepared to rendezvous at Mars. The rest of the Word Bearers Legion was tasked with destroying Roboute Guilliman and his Ultramarines on the world of Calth in the Eastern Fringe of the galaxy.

The Imperial Fists Legion's Primarch Rogal Dorn and the Regent of the Imperium, Malcador the Sigillite, receiving the few survivors from the Drop Site Massacre of Istvaan V as they retreated back to Terra, became aware of the full implications of their position and the strength of Horus and the Traitor forces. Dorn immediately recalled all Loyalist Imperial forces back to Terra in preparation for Horus' invasion. Of the Space Marine Legions still loyal to the Emperor, the Space Wolves had just completed the Burning of Prospero, the Thousand Sons Traitor Legion's homeworld near the Chondax System, where the White Scars were stationed. Without warning, the Alpha Legion's fleet broke from the Warp and engaged the Space Wolves, hammering their smaller fleet and forcing Leman Russ to resort to hit-and-run attacks. The Alpha Legion's Primarch Alpharius also attacked the nearby forces of the White Scars piecemeal in an attempt to draw that larger Astartes Legion into conflict.

The White Scars' Primarch Jaghatai Khan wished desperately to aid Russ, yet as the Traitor Legions' starships attacked, he received the astropathic order from Rogal Dorn. Khan was to bring his Legion back to Terra, immediately. Dorn also commanded him to relay the order to Russ and add that should he succeed in evading his attackers, only then should he attempt to head for Terra. Relaying the message and adding his apology for his inability to aid the Space Wolves, the White Scars made for Terra. Russ resolved to meet the Alpha Legion with renewed determination. With help from an unlikely quarter, the Space Wolves would eventually turn the tables on their attackers and make the Warp jump to Terra, well after the siege on the Imperial Palace had begun.

Similarly at the world of Calth, the Ultramarines expeditionary force, battered by the relentless attacks of the Word Bearers, had dug in on the planet's surface, while their Primarch Roboute Guilliman and the remnants of his fleet began to organise hit-and-run attacks. Surveying the scene on the planet, Guilliman rapidly assessed his ground troops' positions, and began broadcasting orders to his men, coordinating each pocket of defence. One such pocket, under Brother-Captain Ventanus, organised a breakout, and retook Calth's planetary defence cannons and laser silos, reaping a great tally of Traitor starships. Ventanus' victory evened the odds in space, buying time for the vast remainder of the Ultramarines Legion to arrive at Calth and drive the Traitors away. Reunited as a single force, the Ultramarines received Malcador's orders and set out for Terra, moving through the Warp as rapidly as they could even as they realised that they would probably arrive too late to make a difference.

As this happened, the Night Lords arrived in the Eastern Fringe of the galaxy to engage the Dark Angels, and the Iron Warriors' armada broke from the Warp to engage the Imperial Fists' fleet marooned near the Traitor Legions' headquarters world of Istvaan V. Surviving the initial thrust of the Iron Warriors' attacks, the Imperial Fists' armada held fast and scattered Perturabo's fleet, then made their own Warp jump to Terra in a desperate race against time.

Meanwhile, in the Signis Cluster, the Blood Angels, granted new and terrible power by a mysterious mass rage that would resurface again during the Battle of Terra had triumphed, smashed the hordes of the Chaos daemons they had faced asunder and were able to make the Warp jump to Terra.

As the Warmaster was heading towards Terra he received an unexpected communication from the recently betrayed Thousand Sons Primarch Magnus the Red. Magnus pledged his allegiance and the allegiance of the Thousand Sons Legion to Horus and Chaos in retaliation against the Emperor for his betrayal of the Thousand Sons and the destruction of their homeworld of Prospero. The Thousand Sons informed the Warmaster that they were en route to Terra where they would link up with Horus' forces.

Of the nine remaining Loyalist Space Marine Legions, only the White Scars and the Blood Angels were able to join Rogal Dorn and his Imperial Fists in the defence of Terra before the arrival of the Traitor Legions in the Solar System. Three entire Titan Legions of the Adeptus Mechanicus and close to two million soldiers of the Imperial Army stood alongside them to face the Traitors in a battle that would determine the fate of Mankind for 10,000 years.

Landing on Terra
The Battle of Terra began with an orbital bombardment by the Warmaster Horus' fleet as the prelude to invasion. Although the Loyalist fleets and defenders fought back and the massive orbital defences on Luna reaped more than a quarter of the starships in the Traitor fleet they, like the Loyalist soldiers on the surface, were too few to face the combined forces of so many Traitor Legions, and were mowed down without mercy. After days of bombardment, the Chaos Space Marines landed on the surface of Terra in Drop Pods and advanced on the two spaceports nearest the location of the Imperial Palace to secure them in preparation for the main landings of the Traitor forces. Elements from five of the Traitor Legions participated in the battle, aided by the Traitor forces already on the surface. Despite the brave efforts of the Loyalists, the Eternity Wall and the Lion's Gate Spaceports fell within hours to the Forces of Chaos. Dark Chaos Cultists made their invocations, calling down the Greater Daemons of Chaos from the Warp directly onto Terran soil. With the spaceports secured, Horus' remaining troops of the Traitor Legions and their Traitor Imperial Army and Dark Mechanicus support forces landed en masse, and the hulking transports carried thousands of troops each. They also landed the terrible Traitor Titans that served the Warmaster's cause and had been infected with the daemonic power of Chaos. The transports' immense size made them prime targets for Terra's defence lasers. Although many of the Traitor landing craft were destroyed in-atmosphere, many more made it to the surface, disgorging yet more soldiers, main battle tanks and Traitor Titans to add to the besiegers' strength. They met stiff resistance from the Loyalists as the Imperial defenders knew that the survival of the Mankind's homeworld, their Emperor, and the future of the entire human race rested on their shoulders.

The Siege


The Chaotic besiegers forced the Imperial defenders back to the walls of the Imperial Palace, where thousands died slowing the assault. The Primarch Angron of the World Eaters Legion, now a Daemon Prince of the Blood God Khorne, came forth before the walls of the Palace and demanded the Loyalists' surrender, saying that they were cut off, outnumbered, and defended a ruler unworthy of their loyalty. Many would have surrendered to Angron after seeing the sheer power of the Forces of Chaos that stood arrayed before them had it not been for the Primarch Sanguinius, the winged and seemingly angelic leader of the Blood Angels Legion. The two Primarchs, once brothers, gazed at each other, perhaps communicating telepathically. Eventually Angron withdrew from before the gates of the Imperial Palace, telling his forces, not without some relish at the prospect of slaughter, that there would be no surrender.

The siege of the Imperial Palace then began in earnest. Three times the Forces of Chaos scaled the walls, and three times were hurled back by Sanguinius and his Blood Angels. Outside the Palace walls, Space Marine and Imperial Army forces led by Jaghatai Khan, the Primarch of the White Scars Legion, unsuccessfully tried to draw the bulk of the besiegers' army away from the Palace. Soon the outnumbered defenders were pushed back into the maze of corridors and bulwarks within the Palace walls. Frustrated with his army's slow progress, Horus ordered the Legio Mortis (Death's Head Legion), a Traitor Titan Legion, to demolish entire sections of the wall. Despite grievous losses, the Titans, led by the infamous Imperator-class Battle Titan Dies Irae, gouged open breaches in the Imperial Palace's defences, which the Traitors then flooded through.

Facing a breach and potential collapse of the Imperial defences, Jaghatai Khan decided on a change of plan. Rather than assaulting the almost-invincible flanks of the Chaotic army, Khan redirected his highly mobile White Scars Space Marines and the surviving Loyalist Tank Divisions of the Imperial Army to Lion's Gate Spaceport. At dawn Jaghatai's lightning raid caught the Traitor garrison at the spaceport completely by surprise, and reclaimed the spaceport for the Imperium. The Khan ordered his troops to reactivate the spaceport's defence lasers to prevent the Traitor fleet from bringing down any more troops and equipment and form a defensive perimeter to hold their newly reconquered territory. Khan's troops repelled several frenzied counter-attacks from the Traitors, and began firing on Horus' unprotected drop ships. The Khan's plan worked perfectly: the flow of the Traitors' men and machines to the Imperial Palace had been cut in half at a single stroke. Inspired by this success, the Loyalists also tried to seize back the Eternity Wall Spaceport, but were driven back by the Chaos forces without difficulty, as they had reinforced their garrison following the loss of the Lion's Gate.

Inside the Palace, the defenders had been forced back to the Eternity Gate, the sole point of entry into the inner sanctum of the Imperial Palace. The Astartes of the Blood Angels and Imperial Fists tried to hold back the attacking Chaotic troops, while the remaining Loyalists made it through the Gate. Soon the mighty Bloodthirster Greater Daemon Ka'bandha came forth and bellowed out a challenge to Sanguinius in the name of his master Khorne. The daemon hurled itself at the Angel of Baal, barely allowing him time to parry the daemon's strikes. The two took to the air, trading blows and battle cries high above the heads of the two forces. Already fatigued from the long siege, Sanguinius was cast down by the daemon, pulverising the ferrocrete below upon impact. The Loyalist forces seemed to collectively groan at the fall of their great champion.

Yet the Blood Angels' Primarch was not beaten, only stunned by the force of the impact. Sanguinius cleared his head, forced himself back to his feet, and once again took to the sky. The Angel seized the gloating daemon, holding it by the right ankle and arm. The Primarch hefted the creature high and broke its back over his knee, before hurling the daemon's carcass back at the besiegers, who howled in despair as the last Loyalists fell back and made it into the Imperial Palace's inner sanctum before the great portal of the Eternity Gate was shut tight behind them. Of course, as a daemon, Ka'bandah could not truly be slain, only banished to the Warp for a 1000 standard years, but the Bloodthirster's spirit was sent howling back into the Immaterium to meet the displeasure of his master the Blood God.

The Eternity Gate was closed.

Inquisition
The Warp Gate the Emperor had constructed deep beneath the Imperial Palace and the short section of Webway passage beyond required constant maintenance lest they fall into ruin. At first this demanded only a small portion of the Emperor's psychic might and so He was able to command His armies and do all that was expected of Him as Emperor. But the hideous monstrosities that ruled the Warp -- the self-proclaimed Gods of Chaos -- had ever been his foes, and now conspired to subvert the Emperor's goals as they had since the day He had launched the Great Crusade. To this end they had tempted the naive Magnus the Red to warn Him of the very plot they had initiated, the betrayal of the Imperium by Horus. Magnus sent his warning by means of powerful psychic sorcery and this broadcast had wreaked havoc upon the protective psychic shielding surrounding the Emperor's fragile Webway construct. The spell of Magnus not only allowed the foul denizens of the Warp entry to the section of the Webway the Emperor's secret army of Adepts and Tech-priests had by then conquered, it destroyed the delicate controls the Emperor had set in place. Now the Warp Gate he had constructed required virtually all of His psychic power and mental concentration lest it rip open a permanent doorway between Terra and the Warp, flooding the homeworld of Mankind with the daemonic legions of the Ruinous Powers.

The Emperor told Malcador that he had to take the Emperor's place on the psychic amplifier known as the Golden Throne, which provided the psychic sheath needed to protect the new, human-built sections of the Webway intended to be the Emperor's final gift to humanity before the Horus Heresy had begun. The Emperor's original choice of His replacement on the artefact had been the Primarch Magnus the Red, but since Magnus and his Thousand Sons Space Marine Legion had sided with Horus and the Chaos God Tzeentch, Malcador was now His chosen successor and the only remaining human psyker with enough strength to carry out the duty.

In the days before the final confrontation between the Emperor and Horus aboard his Battle-Barge the Vengeful Spirit during the Battle of Terra, the Emperor ordered Malcador to summon twelve "..men of character, skill and determination" who would be tested and trained to become the elite group of investigators intended to root out treachery across the Imperium in the centuries to come to prevent any event like the Horus Heresy from occurring again. The Emperor also told Malcador to prepare himself for the dreadful sacrifice that he would be called upon to make.

Malcador the Hero
The Terran Warp Gate would remain closed to the daemons for as long as the Emperor was able to power it from His throne atop the golden portal. Only the mightiest of human psykers had power enough to do this and even then most would be exhausted and fail in a short time. Only the Emperor Himself had the might to keep the gate closed permanently and for Him the effort grew harder as the daemonic forces gathered about Him. For as long as the daemon horde threatened to breach the portal, the Golden Throne would be His prison. As Horus' forces began their final assault on the Sol System and the Battle of Terra began seven standard years after the Traitors had first turned upon the servants of the Emperor at Istvaan III, the Sigillite returned from his mission to recruit the foundation of the Inquisition. Only through the most artful of psychic subterfuge were Malcador and his new recruits able to pass unscathed through the battlelines and come unharmed and unseen before the Emperor within the inner sanctum of the Imperial Palace.

Malcador had finally received the call and was now prepared to perform his final duty to the man he had followed for the greater part of his life. Once within the depths of the Imperial Palace, the Emperor asked if Malcador was prepared to take his place upon the Golden Throne. Ever loyal, the Sigillite was more than willing to sacrifice himself for his Emperor. But before he ascended to take his place upon the Throne, the Sigillite had one last duty to perform. He was accompanied by a group of twelve hooded attendants. In stern silence the Emperor surveyed the robed figures that Malcador had brought before him, and he saw that his faithful servant had done well. Of the twelve, four were mortal lords and administrators of the Imperium possessed of an inquisitive nature and unyielding strength of mind. The other eight were Space Marines whose abilities were as peerless as their dedication to the Emperor. Some hailed from Legions that had abandoned the Emperor's light in favour of Horus' dark promises, but these Battle-Brothers had never lost their loyalty and had fought the Heresy from within. Fulsome in his approval of the selection, Malcador the Sigillite ascended to the Golden Throne, replacing the Emperor who now stood before the edifice with his loyal captains Rogal Dorn and Sanguinius.

Malcador could not speak, such was the concentration he had to bring to bear in order to control the tempestous forces at his call. The Emperor directed the attention of the two mighty Primarchs, "Behold the greatest sacrifice of our age! Malcador the Sigillite is no more. Henceforth he shall always and only ever be Malcador the Hero!" At this the three figures retired from the Imperial Palace's vault and made ready to teleport onto the Battle-Barge of Horus. The task of keeping the daemons out of the Imperial Palace was daunting for the Emperor, the mighty reincarnation of a thousand human psykers with millennia of experience to call upon. Though he was a powerful psyker in his own right, Malcador was still but a mere human, his mental powers nothing compared to that of the Emperor, and this task proved overwhelming, consuming him body and soul in a matter of hours.

Endgame
"Sometimes the only victory possible is to keep your opponent from winning."

- The Emperor of Mankind before the Battle of Terra

The siege of Terra following the initial assault on the Imperial Palace lasted for 55 days. Both sides knew that the defeat of the Imperium of Man was near after the defence of the Eternity Gate. Sensing this, and knowing that he must complete the siege before the arrival of Loyalist reinforcements from the other Space Marine Legions that were already on their way, Horus prepared to teleport to the surface from his flagship, the Vengeful Spirit, to lead his forces in person. Before this could happen, the Word Bearers' First Chaplain Erebus broke the news to Horus: their daemonic allies in the Warp had informed them that the Dark Angels and Space Wolves Legions were nearing Terra; and the Ultramarines were only a short distance behind.

At that moment, Horus despaired; his gamble had failed, weeks of further conflict would be needed to break the defenders and the Emperor's reinforcements would arrive in mere hours. What happened next is disputed in the Imperial historiography of the Heresy; some believe Horus disabled his Void Shields as he experienced one last moment of regret for his betrayal of his father and his turn to Chaos, while others believe it was a personal challenge to the Emperor. Nevertheless, Horus lowered the Void Shields of his flagship, the enormous Battle Barge Vengeful Spirit. The lowering of the vessel's shields was detected by the Loyalist vessels in orbit and the information was relayed to the Imperial Palace.

The Emperor of Mankind rose to the challenge, leading members of His elite personal guard, the Legio Custodes, the Primarchs Sanguinius and Rogal Dorn, and several companies of Imperial Fists and Blood Angels Veteran Space Marines in the assault and teleported aboard the Vengeful Spirit. Horus used his Chaotic powers to scatter the Emperor's force throughout the massive warship when they teleported up through the Warp. Each fought a series of battles against the elite Forces of Chaos aboard the corrupted starship, attempting to link up with their comrades and confront Horus. It was Sanguinius who reached his brother Horus first. The Warmaster attempted to turn the Blood Angels' Primarch, his oldest and closest friend among the other Primarchs, to Chaos one last time. When Sanguinius refused to be corrupted, Horus attacked. Wounded from his many battles on Terra and the terrible battle with the daemon Ka'bandah, Sanguinius proved to be no match for Horus, now at the peak of his daemonic power after his long alliance with the Ruinous Powers. Horus strangled the Angel of Baal with ease. An alternate version of this event sometimes recorded in the Imperial records has Sanguinius cutting a small hole in Horus' Terminator Armour before he died, as this hole aided in the Emperor's final defeat of Horus.

When the Emperor finally entered the throne room of the Vengeful Spirit, he saw the winged corpse of the angelic Sanguinius lying at Horus' feet. Horus called the Emperor foolish for refusing the power that the Chaos Gods offered to Men, and timid for not taming them to His will if He was truly the Master of Mankind as He claimed. Horus proclaimed that if the Emperor would kneel before him, then he would spare his life. But the Emperor, tens of millennia older than his misguided and once beloved son, knew well the ancient trap that had snared Horus. The Emperor told the corrupted Primarch that he was the deluded slave of Chaos, not its master, for no mortal could ever truly claim to be more than simply a pawn of the Ruinous Powers. Snarling, Horus hurled bolts of daemonic lightning at the Emperor, but the Emperor nullified them with His own immense psychic abilities. The die was cast. Each god-like being knew that the fate of humanity now hung in the balance.

The Emperor and Horus engaged one another in the throne room of the massive Battle Barge, a battle that was both physical and psychic in nature. Though the Emperor's psychic gifts and martial skills were unequaled, He found Himself unwilling to summon His full strength against His beloved son. The Emperor suffered grievous wounds at Horus' hands, and after a score of thrusts, parries and counter-thrusts between the Emperor's Runesword and his own Lightning Claw, Horus sliced open the Emperor's chest armour, then opened his jugular and severed the tendons in his right wrist, disarming the Emperor. A psychic blast seared the flesh from the Emperor's face, destroying one of the Master of Mankind's eyes. After tearing the Emperor's right arm from its socket, Horus raised his father's broken body high over his head, and broke his back over his knee.

At that moment, a lone Legio Custodes warrior entered the bridge. Horus showed the Imperial bodyguard the Emperor's broken form and laughed at the Custodian. The valiant Imperial warrior roared and charged the Warmaster. He was flayed alive by a glancing psychic blast of Chaotic power from Horus. In other accounts of this final battle in some Imperial sources, an Imperial Fists Terminator attacked Horus; in still other versions, the doomed man is an Imperial Army trooper named Ollanius Pious. The casual brutality of the Warmaster's act galvanised the Emperor as He realised what awaited Mankind under the rule of Horus and the Chaos Gods. Realising at last that His favoured son was truly lost to the corruption of Chaos, the Emperor finally gathered His full and awesome psychic power in the Immaterium and unleashed a lance of pure Warp energy that pierced the gloating Horus' psychic defences and ripped his body apart. In some versions of the tale, this blast was only able to pierce Horus' body through the hole that had been made by Sanguinius before his death. Just before Horus died, he looked his father in the eye, shedding a single tear, begging his father to forgive him for his betrayal. The Emperor saw regret in his fallen son's eyes. The Emperor also knew that the Ruinous Powers could attempt to possess Horus again, and that He would not be there to stop his son again if they did. Driving all of the near-infinite reserves of compassion from His mind for the sake of the humanity He had served and loved all the years of His long life, the Emperor destroyed Horus utterly, his essence burned from existence in both the physical world and the Immaterium so that the Ruinous Powers could not resurrect Horus as a Daemon Prince through their claim on his soul.

The destruction of Horus' soul sent a psychic shockwave surging across the Solar System, casting the daemons of Chaos back into the Warp, and spreading mass panic among the Traitor Legions and other Traitor forces on the surface of Terra in seconds as the Chaos Gods found their powers disrupted temporarily by the death of their favoured mortal vessel. It became clear to the Forces of Chaos that their leader had been defeated. A terrible, berserk fury later known as the Black Rage had encompassed the Blood Angels at the moment of their Primarch's death, and they were surging forth to scatter the attackers. Retreat turned to rout, and rout soon turned to bloodbath; thousands upon thousands of Chaos Space Marines and Chaos Titans fell attempting to flee. The ground before the Sanctum Imperialis ran red with the blood of Traitors and Heretics.

Meanwhile, the Primarch Rogal Dorn finally found his way to the corrupted starship's bridge, only to discover his fallen brother, Sanguinius, and the shattered body of the Emperor, who was now on the verge of death, His remaining psychic energy spent in the battle with Horus. It was then that the Emperor whispered instructions to Dorn, urging the Imperial Fists' Primarch to take Him to the device known as the Golden Throne in the inner sanctum of the Imperial Palace. If there was a chance to save the Emperor's life, Dorn would do what he could.

Ascension
"Whom gods destroy, they first drive mad. Mere toys we are for their pleasure, and those it amuses them to raise up, they soon tire of and strike down for their sport."

- The Dramaturge Procul Soldaris, Circa M2

The surviving Loyalists teleported back to the Imperial dungeons beneath the Imperial Palace. Here Malcador the Sigillite, the Regent of Terra who was himself an extremely powerful psyker, had briefly taken the Emperor's place on the Golden Throne, thus keeping the Warp Gate to the Webway that the Emperor had been building for the benefit of humanity safely closed from an assault by the daemons of the Realm of Chaos. Dorn found Malcador sitting wasted, psychic energy lashing across his shriveled body, tortured by the psychic bombardments of the collapsing Imperial Webway. He was almost dead when the Tech-priests made the exchange -- disengaging Malcador from the strange machine even as they moved to modify it to support the Emperor's crippled life functions indefinitely. As Malcador was removed from the device, the last flicker of life left him and the dust of his corpse blew across the stone floor. Yet Malcador managed to prove one final time his loyalty and love for the Emperor, for despite his ordeal and agony, he still managed to gather what remained of his wasted power, and willingly forsook it to feed the Emperor and allow his master to survive.

This sacrifice restored the Master of Mankind's consciousness so that he could deliver his final instructions to His servants before being interred in the device as the Tech-priests of the Mechanicum worked furiously to modify the Golden Throne to the Emperor's specifications. Malcador's final sacrifice allowed the Emperor to awake from His coma briefly and give His servants their final orders before being interred silently for the next 10,000 standard years within the modified life support systems of the Golden Throne. The Emperor spoke His final words to his followers. He urged them to continue the fight to free humanity from the Forces of Chaos and the machinations of the Ruinous Powers as well as the ignorance that continued to assail it. And then the Master of Mankind spoke no more, His body entombed within the life-support mechanisms of the Golden Throne, his spirit caught between the Warp and a crippled, decaying body for millennia. Unable to complete the Webway project that the Golden Throne had originally been intended to create and maintain, the Emperor now chose to use its psychic augmentation mechanisms both to maintain His shattered body's life support functions and to project His mind into the Immaterium where He would create and maintain the Astronomican navigation beacon to hold the Imperium together. The Emperor would also battle the Chaos Gods on their own plane, always seeking to protect Mankind from their corruption and depredations.

The Imperium of Man had survived the Horus Heresy intact, but would evolve into the bastion of repression, ignorance and brutality the Emperor had long fought against without His direct, guiding hand upon it. In this, at least, the Chaos Gods had won a partial victory, for this state of affairs would ensure that their temptations would continue to corrupt the weaker members of the human race and prevent the final establishment of Order across the galaxy. Yet, for all its terrible and growing flaws over the next ten millennia, the Imperium would also offer humanity its best and perhaps only hope for survival in an uncaring and increasingly hostile universe.

The Great Scouring and the Reformation
As the flames of the civil war subsided across an Imperium in which 2.3 trillion human beings had died and countless worlds had been utterly shattered, the Ultramarines' Primarch Roboute Guilliman rallied the surviving Loyalists, stretching his own Legion thin across the galaxy to buy time for the other Space Marine Legions to rebuild and rearm to take the fight to the remaining Chaos Space Marine Traitor Legions in what became known as the Great Scouring. Although some Traitor Legions had fled to the relative safety of the Eye of Terror, the Iron Warriors continued to hold fast to the worlds they had conquered, and were dislodged only after decades of gruelling warfare. Similarly, the Chaotic Night Lords Legion continued their spree of genocide and terror along the Eastern Fringe of the galaxy. This campaign endured until the Night Lords' Primarch Night Haunter was assassinated on the world of Tsagualsa. Shortly after, Roboute Guilliman slew the Alpha Legion's Primarch Alpharius (but not his secret twin brother Omegon) on the planet of Eskrador.

As the last of the Traitor Legions fled to the safety of the Eye of Terror at the end of the Great Scouring, Roboute Guilliman turned his attention to rebuilding the Imperium of Man itself in what became known to later Imperial historians as the Reformation. Never again would it succumb to a Heresy so vast or destructive. Guilliman divided the Imperial Army into the separate branches of the Imperial Navy and the Imperial Guard, diluting their ability to mutiny en masse by creating a bureaucratic rivalry between the services. The Imperial Inquisition had been founded by Malcador at the instigation of the Emperor at the start of the Heresy to prevent the secret spread of the corruption of Chaos through the ranks of humanity from happening again, and the Grey Knights Space Marines Chapter was later founded from the core group of 8 Astartes gathered by Nathaniel Garro to combat daemonic incursions as part of what later became the Inquisition's Ordo Malleus. The Council of Terra that had been created by the Emperor after the Ullanor Crusade to provide the Imperium with a civilian administration was succeeded by the High Lords of Terra: a Senatorum Imperialis composed of the 12 most powerful individuals in the Imperium who were the leaders of its various governmental institutions known collectively as the Adeptus Terra. The High Lords were to act as the regents of the Imperium and rule in the Emperor's name as they sought to carry out his will.

Of all the changes brought upon the Imperium by Roboute Guilliman after the Horus Heresy, the most pivotal was the Second Founding of the Space Marines. This reform, enacted seven standard years after the defeat of Horus, saw the remaining Loyalist Space Marine Legions broken up into smaller, more flexible 1000-man units known as Chapters, thus transforming the Legiones Astartes into the Adeptus Astartes. Although Rogal Dorn, Vulkan, and Leman Russ opposed breaking up their beloved Legions, Guilliman's initiative had the backing of Corax, Jaghatai Khan and the High Lords of Terra, and the measure passed irregardless of the other Primarchs' opposition, marking the end of the Primarchs' dominance over Imperial life and the imposition of mortal rule that the Emperor had desired. The Adeptus Astartes were granted almost total autonomy from every other Imperial Adepta, including the Inquisition, but not from the High Lords of Terra who spoke for the Emperor. Never again would one man wield the power of an entire Space Marine Legion or have such total control over the Imperium. At the same time, Roboute Guilliman completed his great work, the Codex Astartes, the famed tome that laid out the proper organisation, tactics and order of battle for a Space Marine Chapter. The Codex soon became a sacred tome for the Ultramarines and their myriad Successor Chapters, the backbone of the Adeptus Astartes in the centuries after the Horus Heresy. Other Chapters, like the Blood Angels, the Dark Angels and the Space Wolves, adopted the Codex's guidelines only in part or not at all, a sign of their continuing disagreement, however ineffective, with the reforms of Guilliman.

Continuity
Beginning in 2005, the story of the Horus Heresy has started to be expanded with a collection of art books and novels created by various authors from the Black Library, set in the time period of the early 31st Millennium as opposed to the circa 40,000 AD era of normal Warhammer 40,000 literature. An initial scene-setting trilogy featuring the Luna Wolves and portraying the fall of their Primarch, the Warmaster Horus, and the beginning of the Heresy through the eyes of Garviel Loken, the 10th Company Captain of the Sons of Horus Legion, was released and since the completion of said trilogy, another series of novels followed Battle-Captain Nathaniel Garro of the Death Guard Legion as he created what would become the core of the Grey Knights and the Inquisition. The novel range has expanded to include the actions of other Space Marine Legions during the terrible conflict and the role of the various Imperial Adepta. In some cases the new material introduced in the card game, art books and novels has led to continuity conflicts with the older material, although the information provided in the novel series is generally assumed to be canonical and superseding the older material when a conflict arises, and is the basis for the outline of the Horus Heresy given here.

Chronology of the late Great Crusade and the Horus Heresy
Note: The following information was compiled by manifold and diverse hands at the order of Malcador the Sigillite and the Acting Council of Terra following the outbreak, as well as during, the major events of the Horus Heresy. As more information is uncovered in newly discovered Imperial records, it will be added to the chronology.

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