Hydra Cordatus was an Imperial Forge World and Desert World located in the Segmentum Obscurus near the Eye of Terror and one of the few locations in the galaxy where the Adeptus Mechanicus stored its tithes of Space Marine gene-seed, in this case of the genetic material drawn from the Imperial Fists Chapter.
The planet consisted of only a spaceport and a single large citadel and manufactorum complex known as the Tor Christo. The Tor Christo was a large star-shaped fortress connected to a smaller half-star fortress built into the side of a nearby mountain. The citadel had a large garrison of Imperial Guard troops and even a small Titan Legion to protect its precious contents.
The Great Crusade
The world of Hydra Cordatus was rediscovered and brought into Imperial Compliance during the Great Crusade sometime in the late 30th Millennium or early 31st Millennium by the Expeditionary Fleet of the Imperial Fists Space Marine Legion. Upon the newly discovered world, their Primarch Rogal Dorn had chosen the preexisting fortress known as the Cadmean Citadel as the site upon which to plant the Aquila, not as a symbol of Imperial dominance, but a seat of governance to be shared by all. The elegance with which the Cadmean Citadel had been integrated into the local topology and the surrounding city was breathtaking. No history told who had built this marvel atop the mountain, though the engineers and artisans who had raised its living walls must surely have been the greatest minds of their age.
Wrought from stone and rock unknown to its homeworld and laced with technologies whose secrets not even the Mechanicum could fathom, its walls reacted to damage like living tissue. Shell impacts would scab over with liquid silicates, and moments later the wall beneath would be whole again. Only when the damage done to the wall was sustained and catastrophic, would it prove irreparable. Attackers found the wall reacting to them with spiked extrusions of living rock, or were swallowed whole as the stonework opened up beneath them. Against any conventional foe, the fortress would have been impregnable and indestructible. Rogal Dorn had brought the planet’s former rulers into the establishment of an ordered Imperial planetary government, allowing the people to choose their own Planetary Governor, a respected civic leader named Endric Cadmus. This was an uncharacteristically democratic move for the normally authoritarian Imperial Fists.
Imperial Fists Astartes escorted the Expedition's Iterators and Remembrancers as they went from the world's cities to far-flung townships, spreading word of the Emperor of Mankind to a people ripe to embrace the Imperial Truth. It had been a glorious time, and when Dorn announced that the time had come to lead the VIIth Legion on to fresh campaigns, the populace of Hydra Cordatus had mourned his departure like the loss of a loved one. Captain Felix Cassander given the solemn duty by Lord Dorn to stand with his battle company as sentinels to the newly compliant world, a potent sign that this was a world under the protection of the Imperial Fists. But that honourable gesture was to have consequences that not even Lord Dorn could have foreseen.
Unknown to Captain Cassander, the Imperial Fists officer who had been left in command of the detachment of Space Marines that remained behind on Hydra Cordatus after the main fleet left, the Warmaster Horus had fallen to the corrupting influence of Chaos and had instigated a galaxy-wide rebellion in order to overthrow the Imperium of Man and raise himself up as the new Master of Mankind. Shortly after the disastrous events of the Drop Site Massacre of Istvaan V had played out to their tragic conclusion, the traitorous Iron Warriors Legion saw the opportunity to humble their hated rivals, the Imperial Fists, upon the isolated world of Hydra Cordatus. When the order came from Rogal Dorn for all of the Imperial Fists to return to Terra to begin overseeing the defence of the Imperial Palace, Captain Cassander had begun preparations to depart immediately, but the sudden death of his vessel's Navigator had left the detachments of the Imperial Fists upon Hydra Cordatus stranded until a replacement could be dispatched. The following day, word of the Warmaster's treachery and the massacre on Istvaan V reached Hydra Cordatus. Pride in an honourable assignment was replaced by frustration and bitter disappointment that the Imperial Fists present on the world could not fight alongside their Battle-Brothers, and could not call Horus to account for his perfidy and punish those who had trampled their oaths of loyalty to the Emperor into the dust. But the chance to make war on the traitorous allies of Horus came soon enough.
The Iron Warriors made planetfall in the wake of a saturation bombardment that reduced the valley where 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 Cassander 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 Cassander’s warriors stayed alive kept the enemy from redeploying and bringing their strength to bear elsewhere against the Loyalists. Yet, when the Iron Warriors finally overcame the citadel’s ancient defences and broke open its walls they would run amok. They would slaughter 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 Primarch Perturabo himself spearheaded an audacious attack upon the citadel's defenders, and slaughtered over thirty Imperial Fists Astartes himself in a span of only a few minutes. The rest of the Cadmean Citadel's defenders were slaughtered to a man and the surviving 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, and after the end of the Heresy was repopulated as an Adeptus Mechanicus research station and as a depository for the Imperial Fists Chapter's gene-seed.
13th Black Crusade
Ten millennia later, the world of Hydra Cordatus would once again see the Iron Warriors assaulting the now isolated, barren planet. Sometime during the 13th Black Crusade in 999.M41, an unnamed Chaos Lord of the Iron Warriors Traitor Legion known only as The Warsmith, under the orders of the Forces of Chaos' Warmaster Abaddon the Despoiler, attacked Hydra Cordatus in order to steal the hidden stores of Imperial Fists gene-seed kept there. The Imperial Fists had always been the most hated foes of the Iron Warriors since the days of the Horus Heresy but the Iron Warriors needed fresh Astartes gene-seed to grow their numbers since the power of Chaos tended to mutate their own gene-seed to the point that it was unusable to create new Chaos Space Marines. This Warsmith had the Captains Forrix, Kroeger and Honsou, himself a future Iron Warriors Warsmith, under his command. During the battle, the infamous Traitor Imperator-class Titan, the Dies Irae, was finally destroyed by two Imperial Warlord-class Titans. Yet, in the end, the Iron Warriors defeated the Imperial and Adeptus Mechanicus forces defending the Tor as well as an entire company of Imperial Fists Astartes who had arrived as reinforcements to try and prevent the theft of their genetic legacy.
When the battle was won, the commanding Warsmith, having greatly pleased the Chaos Gods through his victory, was granted his final apotheosis of daemonhood and left for the Eye of Terror. Before his final ascension as a new Daemon Prince, he gave command of his warband to his champion Honsou who would take the stolen Imperial Fists gene-seed back to the Iron Warriors' Daemon World of Medrengard within the Eye. After the forces of Chaos withdrew from the world, the Adeptus Mechanicus vessel Mordekai's Light bombarded the remains of the citadel to dust. By the time it was complete, there was nothing left to indicate that the citadel existed at all, so that the Mechanicus' shame would not be known. Only a lone Imperial Guardsman survived the brutal onlsaught. He was found by an Imperial Fists relief force and taken from the blasted surface of Hydra Cordatus.
- Storm of Iron (Novel) by Graham McNeill
- Dead Sky, Black Sun (Novel) by Graham McNeill
- Angel Exterminatus (Novel) by Graham McNeill