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Map of the Coronid Reach dating to the Horus Heresy displaying the location of Agathon.

The Agathean Domain, also known in some sources as the Agathon Domain, is an alliance of several interlinked star systems in the northern Segmentum Obscurus dominated by the Hive World of Agathon.

The Domain is not truly big enough to be warranted true sub-sector status. It is the outermost and final anchor point of the Imperium of Man before the dark frontier of the galactic north.

At its centre lies the thriving world of Agathon, a Hive World that bears strong resemblance to such famous Hive Worlds as Necromunda or Khur, despite the fact that these worlds are thousands of light years away from Agathon's border.

The system rightly counts as one of the most isolated of the Imperial realm, being surrounded on three sides by the galactic void and only accessible through the tenuous Warp routes of Numinal which link it with the other worlds of the Coronid Reach and the Manachean Commonwealth.


Emblem of the reconstituted 1522nd Solar Auxilia Cohort ("Lord Marshal's Own").

The history of Agathon has always been forged by war. As such, Agathon and the entire Agathean Domain has always been intricately bound to the history of the former 60th Expeditionary Fleet of the Great Crusade and the MaSade family.

The Agathean Domain is located in the outer region of the Segmentum Obscurus where it borders the Ultima Segmentum.

This region of space is one of the oldest centres of human habitation, and the initial human colonisation of Agathon may well lie back as far as the early Age of Technology. Not all the worlds of the Agathon System had been bereft of intelligent life, as a highly substantial population of Ogryns was discovered on the Feral World of Othion.

Surviving both the horrors of Old Night and the lurking dangers of the Age of Strife relatively unscathed, Agathon's surface has always been dominated by the three spires that constitute its principal hive cities. But integration into the Imperium was not swift, nor was it without bloodshed, as Agathon resisted for nearly fifteen standard years against Rogue Trader fleets and smaller Expeditionary Forces.

Imperial Compliance was only achieved through the mobilisation of a far-larger force, the 60th Expeditionary Fleet which had already achieved several successful Compliances but was now severely depleted. At its core stood the 1522nd Solar Auxilia Cohort, also known as "The Lord Marshal's Own," under the command of the famed Lord Marshal Ireton MaSade.

This tactically-brilliant general would lead the 60th Expeditionary Fleet in a successful, if bloody, Imperial Compliance action that would see the purge of the cultic aristocracy that ruled Agathon and its domains added to the Imperium of Man.

In reward for this final victory and a lifetime of service, MaSade and his officers were awarded the right of conquest over Agathon and became the new ruler of its five billion inhabitants. The 60th Expeditionary Fleet was disbanded and most of its vessels entered the Agathon System Defence Forces whilst its troopers became the world's new ruling elite.

These loyal subjects of the Emperor who had fought countless wars in His name would see that Agathon became one of the most productive and organised worlds of the Segmentum Obscurus Orient; for the descendants of the 1522nd Cohort would guarantee that their world would ever be ready to fight for itself.

The Horus Heresy

By the closing days of 006.M31, following the fall of the worlds in the Cyclops Cluster, local Imperial powers were girding for war. Though still distant from the front lines of this new civil war that now ravaged the domains of the Imperium, the leaders of the Agathean Domains knew that they could not stand alone against the might of the Warmaster Horus' Traitor Legions and the forces he had already arrayed behind him. So it was that when Grand Admiral Ospheus LaBray called for a mustering of Loyalist vessels at the Armada Imperialis base at Port Maw, the Agathean Domain sent out a full Cruiser squadron bearing the best of the Agathean Domain to reinforce the gathering warfleet.

Severely damaged during the Treachery at Port Maw, the surviving Agathean Cruiser, the Telemachus, limped back to its homeworld bearing word of Horus' victory and the betrayal of the Emperor by the Cyclothrathine Mechanicum. On board the Telemachus also rested the stasis-held corpse of her former captain, Jocasta MaSade, granddaughter of Ireton MaSade. Despite being mortally wounded, she had valiantly refused to be treated as long as her ship was not yet safe and successfully escaped pursuing elements of the Traitors' fleet before succumbing to her wounds. The arrival of the Telemachus would spark the powder keg of fear and political divisions that had been fermenting on Agathon.

Agathon's isolation had protected it from the Warmaster's gaze because as a relatively minor Hive World compared to those of the nearby Manachea System it held little strategic value and had hence been completely bypassed by the Traitors' armed forces. The fear inspired by the fate of such neighbouring worlds as Manachea or Moab grew into civil unrest until even Agathon's Parliament of Electors slipped into open conflict.

Debates raged between die-hard Loyalists, those that would cast their lot with Horus in fear of the consequences of not doing so and those who would secede entirely from the Imperium and return Agathon to independence. Blackmail, threats and assassinations were rife as the wheels of the Agathean government became paralysed and the Hive World teetered on the precipice of all-out civil war.

Into the warring chamber of the Parliament of Electors came Ireton MaSade, nearly two Terran centuries old and almost a recluse for two solar decades. He had not come alone, for behind him was the body of his granddaughter, carried upon an anti-gravitic, floating stasis bier and flanked by a troop of Solar Auxilia Velitaris armoured in a livery of ice white in deference to Agathon's traditional colour of mourning.

Stunned into silence by this most unexpected appearance, the Chamber was forced to listen as Ireton MaSade spoke, first of grief and sacrifice, then of the dream of the Imperium, of human unity and the Imperial Truth. As his oratory turned to rage at the moral weakness of his successors, he denounced the Parliament and declared them traitors to the Emperor as the funeral guard turned their Volkites on them and burned the fractious noblemen to ashes.

Agathon and the other worlds of the Domain would be placed under martial law and controlled by the "Old Guard" of the 60th Expeditionary Fleet and their direct descendants. Almost immediately, Agathon's economy and society were put on a war footing not only in order to defend their Domain but to mount an attack on the Traitors. One way or another, Ireton MaSade would have his vengeance, no matter the cost.

Notable Military Campaigns

  • The Agathon Compliance (Unknown Date.M30) - For fifteen solar years Agathon successfully resisted Imperial efforts to subjugate it. Following earlier failures, the Imperium diverted the 60th Expeditionary Fleet under the command of Lord Marshal Ireton MaSade to break the deadlock. The men and women of the 1522nd Solar Auxilia Cohort prosecuted the Imperial Compliance campaign with zeal and are granted Right of Conquest over Agathon for their efforts. Ireton MaSade became the new Imperial Commander of the Imperial world of Agathon. This marks the beginning of the Agathean Domain.
  • Treachery at Port Maw (008.M31) - Following the muster call of Grand Admiral LaBray, the Agathean Cruiser squadron suffers severely from the betrayal of the Cyclothrathine Mechanicum vessels. Only the Telemachus escapes and returns safely to Agathon. However, her mortally wounded captain, Jocasta MaSade, succumbs en route.
  • Battle of Bodt (008.M31) - Having escaped destruction during the Manachean War, elements of the 1522nd Solar Auxilia Cohort -- approximately 12,000 men and supporting super-heavy tanks detachments under Lord-Colonel Vossen -- join together with other Loyalist elements under the command of Autek Mor to assail the World Eaters' recruiting world of Bodt. Deployed as part of an interdiction force in the southern regions of Tredecimmia, the 1522nd held off several waves of robotic Battle-Automata and other battle-engines spawned by the twisted minds of the Sarum Dark Mechanicum Tech-priests to join the main fight. The Agatheans valiantly held the line before staging a bitterly fought withdrawal, mere solar hours before the entire planet was ravaged by the collision of its moon.
  • Liberation of Numinal (009.M31) - Ireton MaSade personally led the Loyalist counter-invasion of the still-contested Agri-world of Numinal against the hated Cyclothrathine Mechanicum. In alliance with the Imperial Knights of House Orhlacc, the Loyalists use the captured vessel of Rogue Trader Charid Udine, The Hammer of the Deep, to covertly approach the star system's astropathic relay on the moon of Quachil. The destruction of the relay marks the beginning of the Liberation of Numinal proper, with thousands of troopers from the Agathean Cohorts establishing a first beachhead on the planet and digging in. Expecting the reinforcement of the Agathean Cruiser squadrons, the enemy leader of the Dark Mechanicum forces, Archmagos Draykavac, orders his troops to crush the beachhead before more troops can land. In the ensuing battle, Cyclothrathe's robotic Battle-Automata suffered greatly as Ireton MaSade had taken the precaution to equip his troops with augmented blast-chargers, thus increasing the stopping power of his Tercio's lasrifles. Badly mauled and thrown back by the devastating close-range firepower of the Agatheans, Draykavac's forces retreated. By now secondary incursions and several insurrections where happening all across Numinal. Calculating that victory was still possible, Draykavac mobilised his remaining forces for another assault on the Loyalist landing zones. Exploiting the Loyalists' lack of heavy armour, the second assault would benefit from the support of the Knights of House Atrax and House Ærthegn. Expecting a total victory, Draykavac himself took to the field. It was, however, precisely what Ireton MaSade had intended. In high orbit the Hammer of the Deep launched two brutal-looking drop-ships, ancient Khobol-class Heavy Assault Landers older than the Great Crusade itself. With an eardrum-splitting dirge, the Knights of House Orhlacc and their allies of House Hermetika and the Renegade Ærthegn Knights announced their presence on the battlefield. As Knight met Knight, the Agathean Cohorts surged forward from their defensive positions, putting the pressure on the Cyclothrathine Taghmata. All across Numinal, Draykavac's forces were coming under assault as Loyalist Astartes and Auxilia-led insurrectionists attacked and destroyed the Mechanicum conversion crawlers which had until now been protected by the Cyclothrathine Knights. Surrounded and in an inferior position Ireton MaSade's intent became clear: to kill Draykavac and thus throw the enemy into confusion. Recognising the danger he had put himself in, the Archmagos did not hesitate. He sacrificed his oath-bound Knights of House Atrax and his Taghmata forces to ensure his retreat to his command compound from where he would flee the planet. Numinal once again belonged to the Imperium.
  • Raid on Cerada Secundus (009.M31) - Four solar weeks after the successful liberation of Numinal, the Agathean fleet attacked the vessels of Forge World Cyclothrathe, supporting the conquest of Cerada Secundus. However, against the massed war arks of the Taghmata Cyclothrathe, the Agathean Cruisers would not be victorious. With severe losses, the Cruiser squadrons retreated, but their efforts had not been entirely in vain: their presence forced the Taghmata to consolidate its positions, thus opening a new front and forcing the Archmagos of Cyclothrathe to retreat from Cerada Secundus.
  • Defence of Jollov (932.M41) - When Techno Magus Stannum Vir discovered valuable fragments of an STC device on the Agri-world of Jollov, before he could reclaim it, he had to first contend with a vanguard tendril of the newly emergent Tyranid Hive Fleet Moloch. The Great Devourer threatened to consume the world before the STC fragment could be discovered. At the Tech-priest's behest a courageous defence of the planet's spaceport ensues. Elements of the Catachan, Mordian, Kanak, Molov and Agathon Astra Militarum regiments die to buy enough time for the Adeptus Mechanicus to flee with the valuable technological relic.


The culture of Agathon possesses an overriding military aesthetic and the world's military forces, the Agathean Cohorts, can boast a direct lineal descent to the initial Solar Auxilia Cohort of the 60th Expeditionary Fleet. Trained and equipped in the traditions of the Solar Auxilia, the Agathean Cohorts form a sizable and impressive military host with the resources of an entire star system at their disposal. Their reputation for excellence has been well-deserved, as they have successfully defeated alien invasions and would go on to distinguish themselves during the dark days of the Horus Heresy and the Imperium's campaigns.


  • Agathon – Agathon is a spire-type Hive World, its population housed in three distinct hives which owe many similarities to those of Necromunda or Khur. The world is highly organised and constitutes the industrial and economic centre of the entire Agathean Domain. It is undoubtedly the capital world of the Agathean Domain, having imposed its name on the system's alliance and protecting the planets within with its military might. Its population consists both of the original inhabitants of Agathon and the descendants and survivors of the soldiers of the 60th Expeditionary Fleet who brought it into Compliance. In particular, the fleet's officer cadre had integrated with the local noble families to such an extent that within a few generations, the lines between them had blurred. However, the further down the social ladder, the more indifference and resentment was encountered in regard to Imperial rule on Agathon. Prior to the events of the Horus Heresy, but after Ireton MaSade's retirement as Imperial Commander, Agathon was ruled by a corps of representatives called the Parliament of Electors which had been dominated by a strong Imperial faction. However, the events of Horus' rebellion would give voice to the underlying resentment of the Imperial conquest and warrant the return of Ireton MaSade as Imperial Commander to maintain loyalty. This change in regime quickly reimposed order and purged the ranks of the Parliament of its dissidents.
  • Legatus – Originally organised as a penitentiary mining colony for the dissidents of Imperial rule in the aftermath of the Agathon Compliance, by the dawn of the 31st Millennium, Legatus had become the secondary world of the Agathean Domain and its most important Mining World. The landscape of Legatus is dominated by vast tundra plains still locked in the closing stages of a climatic ice age. The planet is immensely rich in high-grade metallic ores that Agathon needs to feed its macro-industry and modest orbital shipping yards. Since 940.M30, Legatus has been subjected to three significant xenos raids; twice by Ork marauders and once by heavily mutated xenos cryptids thought to originate from the extra-galactic void. This led to a sizable military mobilisation. Legatus' standing garrison of Agathean Cohorts was greatly augmented and extensive ground defences were constructed. These would prove invaluable in the dark days of the Horus Heresy.
  • Noricium
  • Othion – Othion is a Feral World of little strategic value were it not for its native Abhuman population. An excessively arid world due to its lack of cloud cover, Othion seemingly consists of limitless silica dune seas continuously exposed to the light of its yellow sun. The world is called home by a sizable population of Ogryns who have undergone severe metabolic alterations from the standard accepted types to better accommodate the harsh climatic conditions. This however has led to a severe devolution of the already limited intellect of the Ogryns, resulting in an inherent lack of social cohesion and mental stability. Perhaps most macabre is the pronounced drive to cannibalism of these Abhumans as well as an irrational hunger, which makes them extremely dangerous for humans. Through extensive cranial surgery and the implementation of a "kill-switch" device to terminate them when needed, these Ogryns did, however, prove a powerful addition to regional defence forces. During the Horus Heresy, Othion's Ogryn population would constitute a considerable strategic resource which would be ruthlessly exploited by the Agatheans to bolster their standing military in anticipation of a Traitor invasion; transformed into Charonites, these Ogryns could surpass both Traitor Legiones Astartes and the creations of the Dark Mechanicum in terms of brute strength. This resurgence of Charonite squads was fairly common amongst technically advanced Loyalist systems that had been cut off from other Imperial territories.
  • Turhal
  • Wychval - Very little is known about this savage world at the very edge of the Agathean Domain and the known galaxy. During the bleak years of the Horus Heresy, a deal was struck between Ireton MaSade and High Seneschal Valdemar Orhlacc of House Orhlacc: a new world to call home in exchange for the military might of its Knights. This alliance would bear its fruits many times over, most notoriously during the Liberation of Numinal in 009.M31.
  • Zarnov - Zarnov is an isolated industrialised world that lies to the galactic north of the Coronid Prohibition Zone. This has led the cartographers to attach Zarnov to the Coronid Reach rather than to the Grail Abyss, which features the sole known stable Warp-route leading to the planet. Not truly part of the Agathean Domain due to its peculiar location, Zarnov's battle honour nevertheless is proudly displayed on the Vexillia of the 1522nd Cohort.

Military Forces

  • Battlefleet Agathon - As something akin to an Imperial Sub-sector, Agathon fields its own squadrons of warships. Agathon's industrial might permits the construction of Escort and even Cruiser-sized vessels. At the time of the Horus Heresy, Battlefleet Agathon consisted of at least two fully-equipped squadrons of dark-bronze Cruisers of different types, all bearing the fiery lantern-sigil of the Agathean Domain.
  • 1522nd Solar Auxilia Cohort ("Lord Marshal's Own") - The original 1522nd Cohort participated in the Agathon Compliance campaign and established itself as the ruling elite of this new Imperial world. By the beginning of the Horus Heresy it had grown to become an elite force that formed the heart of the Agathean forces. Thanks to the charismatic figure of its commander, the Lord Marshal Ireton MaSade, his tactical genius and his nigh-bottomless coffers, the newly recreated 1522nd Cohort is a highly mobile and well-equipped force: the entire infantry complement is transported in Dracosan Armoured Carriers and each infantry sub-cohort benefits from its own dedicated armoured support squadron. At High Command level the 1522nd can field a number of dedicated armoured sub-cohorts, three mobile artillery sub-cohorts as well as two dozen Malcador Heavy Tanks that form a heavy armoured assault cadre.

Agathon Domain Regimental Appearance

The Equis Astra -- the original icon borne by Solar Auxilia Cohorts of the 60th Expeditionary Fleet

Descending from a proud military tradition, Agathon has mostly conserved the trappings and emblems of its founders. As such the Equis Astra, the original emblem of the 60th Expeditionary Fleet, can often be found next to the reconstituted sigil of the 1522nd Cohort.

As its name indicates for those versed in High Gothic, the Equis Astra is a typical horse head-emblem the like of which has been in use for uncounted millennia, with the Agathean variant fielding a white horse head on a green field. At the time of the Horus Heresy, this emblem was commonly worn as a cross-unit badge of unity.

The 1522nd Cohort's emblem is an antique crested helmet as worn by the legendary Spartans of Old Terra. It is perhaps in reference to these legendary warriors that the Agatheans' primary colours are noted as dark bronze and green, supplemented by white details where needed.

Notable Vehicles

  • Telemachus - Cruiser of unknown pattern of Battlefleet Agathon, former command of Jocasta MaSade, grandaughter of the famed Ireton MaSade that would distinguish himself during the Heresy. The Telemachus was the sole survivor of the eight Agathean Cruisers sent to the great Armada Imperialis muster at Port Maw. Its courageous escape from the trap sprung there and its arduous return would set events in motion that determined the Agathean Domain's participation in the Horus Heresy.
  • Terra's HammerMalcador Heavy Battle Tank. Terra's Hammer is an illustrious battle tank, a veteran of the Agathon Compliance campaign that would go on to fight during the wars of the Age of Heresy.

At Present

The martial tradition of the Solar Auxilia lives on in the Agathean regiments of the Astra Militarum which have since then acquired great honour in the service of the Imperium. To this day, Agathon still greatly contributes to the Imperial war effort within the Segmentum Obscurus. More recently in Imperial history, the Agatheans' courage and sense of duty was commended in 932.M41 for their defence of the Agri-world of Jollov in the Ghoul Stars region against the Tyranid menace.

Through their valiant efforts at the side of other Imperial Guard regiments as diverse as the Catachan Jungle Fighters, Mordian Iron Guard and regiments drawn from the worlds of Kanak and Molov, the Agatheans ensured the withdrawal of Techno Magus Stannum Vir and the valuable STC fragments he had uncovered on Jollov before being overcome by the chitinous hordes of Hive Fleet Moloch.


  • Codex: Imperial Guard (5th Edition), pg. 23
  • The Horus Heresy - Book Four: Conquest (Forge World Series) by Alan Bligh, pp. 54-63, 74-75, 90-95
  • The Horus Heresy - Book Six: Retribution (Forge World Series) by Alan Bligh, pp. 103-115