Siege of Terra

The Battle of Terra, also called the Siege of Terra or the Siege of the Imperial Palace in Imperial records, is a reference to the final confrontation of the Horus Heresy that raged on Terra in the early 31st Millennium between the Forces of Chaos led by the Warmaster Horus and the Loyalist armies of the Imperium of Man led by the Emperor of Mankind Himself. The Loyalist forces ultimately proved victorious, though only just barely, and Horus was slain by the Emperor on the deck of his massive Battle Barge the Vengeful Spirit, though the Master of Mankind was mortally wounded and had to be interred within the cybernetic life support mechanisms of the advanced psychic augmentation technology known as the Golden Throne. The outcome of the Battle of Terra shaped the destiny of humanity for the next 10,000 standard years.

Preparations
After the Drop Site Massacre conducted against the three Loyalist Space Marine Legions of the Salamanders, the Iron Hands and the Raven Guard by the Traitor Legions loyal to the Warmaster Horus on the world of Istvaan V, it became clear that eight of the eighteen 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 Traitor Legions as their new overlord, supported by elements of the Imperial Army, a portion of the Adeptus Mechanicus and the Titan Legions that had chosen to serve Chaos known as the Dark Mechanicus, strong Imperial naval forces then still part of the Legiones Astartes' Great Crusade Expeditionary Fleets, and the daemon-spawn of Chaos. Over the course of the next seven years of brutal interstellar civil war, their aim soon became clear: Terra, the heart of the Imperium of Man. 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 Fringes 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 Dropsite 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. Rogal 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 forces of the Primarch Leman Russ, hammering his smaller fleet and forcing 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 Palacehad 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 Primarch Roboute Guilliman and the remnants of his Ultramarines' 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, co-ordinating each pocket of defence. One such pocket, under Brother-Captain Ventanus, organised a breakout, and retook Calth's 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 Chaos Space Marines' headquarters world of Istvaan V. Surviving the initial thrust of the Iron Warriors' attacks, the Imperial Fists' armada held fast and scattered the Primarch 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 Siege of Terra) had triumphed, smashed the hordes of the Chaos daemons 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. The Space Wolves had driven the Thousand Sons from their homeworld of Prospero after being manipulated by Horus into attacking the Thousand Sons homeworld instead of simply taking Magnus into custody to return him peacefully to terra to face charges of the illegal use of sorcery by the Emperor. Devastated by the Space Wolves' destruction of his Legion's precious storehouses of knowledge about the Immaterium and sorcery, and having turned to the Chaos God Tzeentch to save himself and his Astartes Legion, Magnus pledged his allegiance and the allegiance of the Thousand Sons Legion to Horus and Chaos in retaliation against the Emperor for this betrayal. The Thousand Sons were en route to Terra where they would link up with Horus' forces.

Of the nine remaining Loyalist Space Marines 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.

Siege of the Imperial Palace
The siege of Terra by the Traitor forces of Horus began with an orbital bombardment by the Warmaster's 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 as well as bringing to the battlefield the terrible Traitor Titans that served the Warmaster's cause and had been infected with the daemonic forces 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 their homeworld, their Emperor, and the entirety of the human race rested on their shoulders.

The Siege
The Chaos 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 defenses, 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 Chaos 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 dropships. 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 Blood Angels and Imperial Fists Space Marines tried to hold back the attacking Chaos 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 siege, Sanguinius was cast down by the daemon, pulverising the concrete below upon impact. The Loyalist forces seemed to collectively groan.

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.

The Endgame
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 battle barge Vengeful Spirit. The lowering of these 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 his elite personal guard, the Adeptus 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 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 the Warmaster's Power Armour before he died, as this hole aided in the Emperor's final defeat of Horus. When the Emperor of Mankind 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 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 unequalled, 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 high over his head, and broke his back over his knee.

At that moment, a lone Loyalist warrior entered the bridge, just as the Emperor fell. Horus, gloating in victory, showed the Imperial warrior the Emperor's broken form and laughed, taunting the Loyalist's uselessness and defeat. The valiant Imperial warrior, far from being daunted, roared in defiance and interposed himself between the Emperor and the Warmaster, heroically holding the line against the Chaos-corrupted Primarch. He was flayed alive for his defiance by a glancing psychic blast from Horus. The exact identity of the brave warrior is a source of much debate amongst Imperial Historians, for today only the Emperor knows the truth. The Adeptus Ministorum tell the story that it was a lone Imperial Army trooper named Ollanius Pius who held the line, going as far as to canonize the man as the Guardian Saint of the Imperial Guard in M32, yet many doubt that mere humans would have accompanied the Emperor and His Primarchs to confront Horus. The Imperial Fists maintain it was one of their Terminators who challenged Horus, however some see this as a desperate attempt to lessen their collective guilt stemming from the fact that Rogal Dorn never could participate in the fighting. Most historians agree that it was probably one of the Adeptus Custodes who interceded, yet the other stories continue to be told and retold over the whole of the Imperium of Man.

The casual brutality of the Warmaster's act galvanised the Emperor as he realised what awaited the 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 defenses and ripped his body apart. In some versions of the tale, this blast was only able to pierce the Warmaster's 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 him 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 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 Traitor Space Marines and 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. 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 Warpgate to the Webway that the Emperor had been building for the benefit of humanity safely closed. Malcador's body collapsed to dust from the sheer strain of holding back the dangers of the Immaterium from coming through the Webway gate and assaulting Terra as he was removed and the Emperor put in his place. Yet the Sigillite imparted his remaining psychic energy before his death to the Emperor to restore the Master of Mankind's consciousness for one final time so that he could deliver his final instructions to his servants before being interred in the device as the Adepts of the Adeptus Mechanicus furiously worked to modify the device to the Emperor's specifications.

The Emperor then 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 in 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 Astronomicon navigation beacon to hold the Imperium together and 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 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.