Gethsamaine Colonus -- or Gethsemane as it is currently called -- is a Hive World located in the former Cyclops Cluster of the Coronid Deeps in the Gothic Sector of the Segmentum Obscurus. It has a long history but is mostly remembered for being the location of the famed Gethsamaine Raid during the dark years of the Horus Heresy, when Loyalist survivors from the Iron Hands Legion conducted a bloody pogrom on the planet. Gethsamaine also holds the dubious honour of being the first Imperial world to have been conquered by the Warmaster Horus' troops on their long March to Terra, and the first human world to be subjected to the so-called Dark Compliance. A populous world, Gethsamaine's position is somewhat precarious as the region of space where it sits is prone to Warp-turbulence, which means that contact with the wider Imperium is intermittent at best.


At the outbreak of the Horus Heresy, Gethsamaine was still a world in the making. Its late discovery, in 942.M30, only sixty-four standard years before Horus' rebellion against his father, meant that the world had been colonised and harboured a sizable human population but had not yet been assigned a specific task. The Imperium had stumbled on Gethsamaine by pure luck as a Chartist liner attempted passage of the void between the Forge World of M'Pandex and Zarnow in the Coronid Reach and went dramatically off-course. Upon its discovery, Gethsamaine was found to be a primordial world with lush, steaming, world-covering rainforests that harboured countless species of primitive flora but where no fauna had yet manifested. It was a virgin world ideally suited for human colonisation. The planet's location at the far edge of the Cyclops Cluster offered untold possibilities for future expansion, and the first colony was rapidly founded in hope of becoming one day the cornerstone of a new Imperial domain that would encompass the surrounding worlds, a place it indeed holds today in the late 41st Millennium as capital of its own Sub-sector. Quickly, numerous Warp-arks were despatched from the teeming hives of the Segmentum Solar to colonise this new world. These settled foremost in the western polar regions of Gethsamaine where the primordial rainforests soon made way for sprawling manufactoria and cities of plasteel and ferrocrete. When the Horus Heresy broke apart the galaxy, these cities dominated the landscape of Gethsamaine, its formerly lush rainforest almost entirely gone. Gethsamaine was now a sprawling Civilised andIndustrialised World with the manpower and military strength to be attributed administrative independence. Void stations and navigational beacons, an Astropathic Choir and naval docks now surrounded the world which had recently begun to mount its own defence monitor fleet. Having heard of the Warmaster Horus' betrayal and the punitive Loyalist expedition gathered to face him at Istvaan V, the authorities of Gethsamaine were content to raise the defence states and wait, confident that the eight Space Marine Legions despatched by the Emperor of Mankind would crush this rebellion. As a mere precaution, security codes were altered and targeting matrices reset to fire at any ship of the four known Traitor Legions, but as so often these efforts would prove in vain.

Messengers of the War to ComeEdit

Surviving records show that the Horus Heresy reached Gethsamaine at 4598.006.M31 when a Gladiator-class Frigate, the Malin Dawn, entered the solar system. The ship belonged to the Emperor's Children Legion and was spotted by vigilant Servitor-gun stations guarding Gethsamaine's astropathic relay as it entered the system's outer reaches, moving slowly towards its core worlds. Already at readiness, high-speed reconnaissance cutters were immediately launched to further investigate this matter. Their close-range scans and Augurs confirmed that the Malin Dawn was badly damaged and more adrift than truly flying. Still wary of the appearance of this derelict ship, but loathe to let it penetrate further in-system, Gethsamaine's warden captain ordered the vessel stopped and boarded. Gethsamaine's two defence monitors, the Gaius Herab and the Brazen Bull, intercepted the Malin Dawn and sent out heavily armed boarding parties of elite Solar Auxilia Veletaris.

The boarding parties encountered no resistance as they entered the frigate, but made a grim discovery. The corridors and halls of the Malin Dawn were covered with the dead. The bodies were mostly Space Marines and crew in the purple of the III Legion, which seemed to have fought each other to the death in brutal close-quarters melee. Other bodies wore the characteristic white and azure of Angron's World Eaters, but all were equally and truly dead. The ship's logs revealed that the Malin Dawn had been a casualty of the desperate battle over Istvaan III, the ship's crew and commander having remained loyal and been attacked by their traitorous kin. In the confusion of battle, the ship had been able to escape full-scale destruction even though it had suffered horrendous wounds and successfully jumped into the Warp. However, once in the Immaterium, the battle within her corridors had not abated and furiously raged on. No clear victor could be identified as both sides had perished to the last man save for her faithful Navigator. For all intent and purposes the Malin Dawn was no more than a flying tomb, tenaciously following her preordained course through the efforts of her Navigator. However upon reaching her destination, her strength had finally abandoned her and the Navigator died without having transmitted her warning, perhaps blissfully ignorant that all her efforts had been for naught for the famous Eisenstein had already carried her warning to the Imperium several solar months before.

Disquieted by this sudden turn of events, Gethsamaine's high command despatched urgent messages alerting Lascal, its closest neighbour, as well the Armada Imperialis facility at Port Maw as the veil between realities was ripped asunder and other vessels appeared.

The Coming of WarEdit

The first voidships to manifest were four Havoc-class Heavy Destroyers bearing the slate grey and bronze of the 507th Attack Squadron, an Armada Imperialis unit that had been part of the Warmaster Horus' 63rd Expeditionary Fleet for more than a standard decade. The real threat manifested shortly after: a Battlecruiser in the dark viridian of the Sons of Horus Legion, a vessel whose name would go on to become synonymous with dark deeds and terrors: the Ikon.

Battle was joined almost immediately, the heavy destroyers opening fire on the Gaius Herab and the Brazen Bull. However their plasma-caster and turbo-lasers put up such a barrier of fire that none of the fusion-warheaded torpedoes launched by the 507th Attack Wing got through. The Gethsamaine defence monitors were powerful ships designed for just such protracted firefights, each one of them boasting the firepower of a Cruiser and the armour of a Battleship in their own right. Their main duty were planetary blockades and picket-duties and compared to the sleek warships they now faced, they were slow and cumbersome vessels; yet their armament proved superior thus far, the dorsal Lances of the Brazen Bull and the Gaius Herab striking through the curtain of fire and torpedoes at the Havocs. Drawn close together to maximise their overlapping fields of fire, the monitors' captains drew on their experience and fell back into defensive tactics the monitors were best suited for. Torpedoes and plasma-gouts still burned across the void, mutually cancelling each other, but all the while distance between the two formations dwindled as the Havocs closed in on their powerful thrusters. So far neither the relentless barrage of the Havocs ' torpedoes, nor the intense cannonade of the monitors had faltered, even if the duel had waxed and waned, it seemed that victory would go to the one who would be able to keep up this punishing regime of fire. Suddenly there was a bright flash and shouts of elation rose on the Brazen Bull’s command deck as one of the Traitor destroyers blazed out of existence, a lucky shot of the monitor's lances having found the Havoc 's plasma-reactor and ruptured its containment field.

Triumph turned at once to horror and despair as a frantic Vox-message from the boarding party on board the derelict Malin Dawn cut through the static: they had seen what the monitors had not, blinded as they were by their own fire and concentrated on the task at hand; using the ongoing battle between the monitors and its Escorts as a diversion, the Ikon had powered-up her massive engines, and burning on over-thrust corkscrewed wide of the firefight to flank the Brazen Bull and her companion. Frantically, the Brazen Bull tried to divert its firepower against this new threat, only to open a gap in the barrage that had so far protected them from the volleys of torpedoes launched by the Havocs. The next volley of the Traitors irremediably found its mark, striking the Brazen Bull amidships just as the Ikon opened up with her Macrocannon batteries. The Brazen Bull was almost ripped to shreds, opened from stem to stern while fires raged in the few compartments not opened to the icy touch of the void. With almost dismissive cruelty, the Ikon passed by the remaining monitor, the Gaius Herab, and released a wave of Dreadclaw assault-pods in its wake. The Gaius Herab valiantly fought on, but it was now desperately out-gunned, the Havocs closing in for the kill. A final volley of torpedoes bracketed the ship, immobilising it shortly before the Dreadclaws slammed home. Squads of Sons of Horus -- once the finest of the Emperor's warriors -– disembarked and ran amok amongst the crew who sold their lives with desperate futility.   

Dark Compliance Edit

Shorn of its most powerful defenders, the Gethsamaine System lay open before the Traitor Hunter squadron. Its remaining watch-posts and gun-stations, unable to directly support each other, were out-ranged and out-manoeuvred one by one and  destroyed. On board the Malin Dawn, the survivors could only watch helplessly as everything they had fought for became unbound. Without the monitors to shield them, Gethsamaine's few static defences couldn't hope to repel these invaders; isolated they were all blasted into flaming debris. On board the Malin Dawn the Vox-link to the Gaius Herab was still active and the boarding party had to witness the screams and pleas of their comrades as the Sons of Horus completed their butcher's work.

On Gethsamaine Colonus, the major inhabited world of the system, planetary defence weapons had been primed and Planetary Defence Forces mobilised, fully expecting to repel an invasion or die at the Traitors' hands; but no attack came. After having blasted the astropathic relay into utter oblivion, the Ikon returned to the devastated wreck of the Gaius Herab to retrieve its complement of Legiones Astartes. Both monitors were by now little more than blood-splattered charnel houses of rent metal, blackened adamantium and dissipating air. Having laid waste to the system's defences the Ikon departed for the Warp as rapidly as she had shown up. But before she left, she left a chilling message, a message which would change in word, but not intent; a message that would be shortly repeated across the Cyclops Cluster and in a hundred star systems; a dark ultimatum which promised a future only of despair and destruction: "Bow before Him who is Warmaster, abase yourself before His truth. Serve those who serve Him, harken only to their words. The Imperium is His. Mankind is His. You are His. Submit to the Warmaster, or die by His hand. There is no other choice, and you will be given the chance to kneel but once. Horus is Lord. Horus is Death."

Without further destruction needed, Gethsamaine surrendered and submitted to the will of the Warmaster, becoming thus the first world to fall under what became known as the "Dark Compliance." Soon, Tithe Aquisitors bearing the baleful emblem of the Eye of Horus where once they had worn the raptor-headed Seal of Terra ruled on Gethsamaine, imposing harsh quotas to be met by Gethsamaine's industries. The rainforests were being cleared in search of valuable minerals or clear-cut to provide fodder for off-world export, but apart from the supplementary hours and the harsh quotas of the Aquisitors, little had changed. Gethsamaine's obedience and submission had spared it from the fates of such worlds as Taracanis or the harsh regime forcibly imposed on the worlds of the former Manachean Commonwealth. This was, however, soon to change.

The Gethsamaine RaidEdit

IH Legion Devastator

An Iron Hands Destroyer Legionary of Autek Mor's infamous Morragul Clan

Just as the unexpected arrival of a lone survivor from the Istvaan III Atrocity in 006.M31 had gone on to herald the dawning of the terrible deeds that were to follow, so the arrival of a second lone ship, this time a survivor of the Istvaan V Massacre would mark the doom to come, for the lone vessel was a warship of the X Legion. When the ill-starred Warp-route from the Grail Abyss tore open once more, the vessel that cut into realspace was no derelict ship as the frigate from the Emperor's Children had been, but a scar-hulled killer, a Grand Cruiser of black iron and crimson blood. The ship's name was the Red Talon and it belonged to the Iron Hands Legion. Its master was the famed and sinister Autek Mor, leader and Iron Father of Clan Morragul which had become the harbour of the most unstable and extreme members of the Iron Tenth. Gethsamaine had been stripped of much of its void-defences by the Traitors, believing the planet secure as it was located far from the front lines of the civil war and the few remaining gun-platforms posed no real threat to the Iron Hands vessel. As soon as these platforms had been silenced, the Red Talon began a heavy and ruthless bombardment of the planet and almost immediately launched a ground assault. Unknown to Gethsamaine's population or the Traitor elements stationed on the planet, the Iron Hands had come with a simple goal in mind: not to liberate or reconquer, but to enact vengeance on those who had betrayed their Emperor.

Any resistance was quickly crushed under the iron tracks of Clan Morragul's battle tanks, an entire cohort of planetary defence militia and their Horusite overseer being obliterated in less than a solar hour. The rout of the other militia elements devolved into a bloody massacre in which one of the X Legion Dreadnoughts, the Contemptor Pattern Dreadnought Veneratii Oberas, distinguished himself. The seats of government were blasted into rubble or flattened from orbit by precision bombardment from the Red Talon's guns; those in positions of power that had sided with the Traitors or helped them were mercilessly and methodically hunted down and executed, except if they were deemed to have potentially useful information, in which case they were dragged screaming and kicking back to the Red Talon's gunships. The bulk of Gethsamaine's population had fled the warfare and only dared come out of hiding once the Iron Hands Thunderhawks had departed. The bulk of the population nervously rejoiced and came forth with praises of the Emperor on their lips, but they were utterly unprepared for what was to come. In each of the five major cities of Gethsamaine, the Iron Hands had left behind improvised atomantic devices fashioned by the bloody hand of their Iron Father. Each bomb was clad in layer upon layer of radioactive material designed to enrich and multiply the fallout generated by their detonation a hundred-fold. As the Red Talon left orbit the bombs exploded; the five cities bloomed into fire, extinguishing the life of millions in a blink of an eye.  

Sentence had been passed on both the real Traitors and those who had knelt before them instead of fighting and dying for their Emperor. The "Raid on Gethsamaine," as it was called, served as a bloody message to those that would bow to the Warmaster, that they were not safe from Imperial retribution and that when this retribution would come, it would be indiscriminate and far bloodier than everything the Warmaster could threaten them with. In the war to come, there would be no innocent bystanders, no civilians to be given quarter to, only Loyalists or Traitors.

Notable Military CampaignEdit

  • The Gethsamaine Raid (circa 007.M31) - Following Gethsamaine's willing submission to the will of Horus and his minions, a splinter-force of of the Iron Hands Legion serving under the grim figure of Autek Mor, Iron Father and chief of Clan Morragul, lands on Gethsamaine. In their quest for information and valuable prisoners to interrogate, the Iron Hands utterly crushed local resistance and purged the population through the use of unsanctioned atomic devices which rendered the world uninhabitable for several standard centuries until its eventual resttlement by the Imperium. The Red Talon then departed the system as quickly as it had come, continuing its rampage behind the lines of the Traitors' advance.
Imperial Navy vs. Chaos Fleet z graves

Lord Admiral Ravensburg's fleet engages the Chaos fleet at the Battle of Gethsemane

  • The Battle of Gethsemane (151.M40) - The Battle of Gethsemane marks the beginning of Lord Admiral Ravensburg's counter-attack during the famed Gothic War. During this prolonged naval battle that was to take place over several solar weeks, Lord Admiral Ravensburg personally led almost the entire might of Battlefleet Gothic against a splinter-fleet of Abaddon the Despoiler's Chaos Armada. The tables were, however, turned when a second Chaos fleet entered the system and tipped the balance of force in favour of the Traitors. Using the stellar dust fields to his advantage, Lord Admiral Ravensburg succeeds in forcing the Chaos fleet to fight his own fleet head-on where the Chaos warships suffered greatly. Trying to escape, the inopportune appearance of an Eldar fleet trapped the Chaos fleet between two gun lines which resulted in a major Imperial victory.


  • Battlefleet Gothic Rulebook, pg. 92-103, 158-159
  • The Horus Heresy - Book Four: Conquest, pg. 22-24, 55, 63, 67, 161

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