Event · M31
Schism of Mars
The Schism of Mars was a civil war fought on Mars in 005–006.M31, during the opening phase of the Horus Heresy. It set the Mechanicum (the priesthood-guild that governed the Imperium’s technology and forges) against itself, dividing the forge world between adherents of Fabricator-General Kelbor-Hal, who sided with the Warmaster Horus, and loyalist tech-priests who held to the Emperor and Terra. The schism grew from years of tension among the Martian Magi over the true nature of the Omnissiah, the Machine God of Mechanicum belief. Kelbor-Hal and his followers had come to regard the Emperor as a false idol rather than the promised avatar of the Omnissiah, and resented the Emperor’s use of Mars as an armoury for the Great Crusade and his prohibition of research into artificial intelligence. When Horus opened secret dealings with the Mechanicum through his emissary Regulus, he offered Kelbor-Hal the means to unseal the Vaults of Moravec, a repository of forbidden lore that the Emperor had ordered sealed. Its opening released so-called scrapcode, a corrupted, Chaos-tainted data-plague that spread through Mars’s cogitator networks and communication systems, sowing confusion that Kelbor-Hal’s faction used to move against those who would not submit to him. Open war followed, drawing in Titan Legions, Skitarii, Knight households and menial workforces across the planet, as forge-cities loyal to Terra, among them those of Zagreus Kane, Koriel Zeth and Ipluvien Maximal, came under assault from the newly formed Dark Mechanicum. Fighting spread from the surface forges to the orbital works above Mars, including installations at Phobos, as fleets loyal to either side clashed in the void. Reinforcements from the wider Imperium, including Imperial Fists Space Marines and a contingent of the Legio Custodes, were despatched to Mars to secure key forges and withdraw what loyalist strength and materiel they could. The Dark Mechanicum ultimately prevailed on the ground, and Kelbor-Hal secured control of Mars for the traitor cause, a victory that deprived the Emperor of his chief armoury at the very outset of the Horus Heresy. Surviving loyalist forces withdrew from the Red Planet, and Imperial forces subsequently blockaded Mars to contain the schism’s aftermath. The episode marked the Mechanicum’s formal fracture into a Terran-aligned priesthood and a Dark Mechanicum bound to the cause of Horus, a division that shaped the wider course of the Horus Heresy.
See where Schism of Mars occurred on the galactic map during the Horus Heresy.