Traitor Titan Legions - Schism of Mars: It is not entirely clear how Horus managed to turn such a significant percentage of the armies under his command against the Emperor, but he was known to be a very skilled and persuasive leader who commanded immense personal loyalty amongst his subordinates. But even before the opening stages of his planned insurrection occurred, he knew he would have to secure the support of the Mechanicum and their superior technology and weapons if he was to defeat the Emperor and conquer the galaxy.Horus won over the loyalty of many of the Mechanicum's Tech-priests after promising them the lost secrets of ancient Standard Template Construct (STC) technology that had been recovered from the worlds of the recently subjugated Auretian Technocracy by the Sons of Horus Legion.The political climate on Mars was full of discontent during this tumultuous time. There were tense relations between the various Techno-magi with sporadic outbreaks of espionage and violence being committed against the various forge cities that represented the primary sociopolitical units of Mars. There were even unconfirmed suspicions that the Titan Legions had already secretly chosen sides in case of a potential civil conflict.Regulus, the Mechanicum's representative to Horus' 63rd Expeditionary Fleet who had already thrown in his lot with the Warmaster's cause, was sent to the Red Planet to secure the tentative support of the fabricator-general of Mars and the overall leader of the Mechanicum, Kelbor-Hal. Regulus convinced the fabricator-general of Horus' resolve to support increased autonomy for the Mechanicum against the autocratic rule and technological restrictions of the Emperor.As a show of his appreciation for the fabricator-general's support, Horus provided information to Kelbor-Hal that allowed the Mechanicum to open a repository of forbidden knowledge known as the Vaults of Moravec, which had been sealed for nearly a thousand Terran years.The Emperor Himself had decreed that the vaults never be opened, for they contained innumerable artefacts of ancient technology that had been fashioned or corrupted by the malign power of Chaos in ages past. But the deal was struck, and the fabricator-general accepted Horus' proposal and joined forces with the Warmaster, assisting the Traitors with all of the most advanced technology of Mankind at his disposal.When this repository was reopened, there was all manner of forbidden arcane knowledge and weaponry that had obviously been tainted by the corrupting influence of Chaos stored within. Soon the corruption spread throughout the forge cities and temples across the Red Planet as scrap code -- Chaos-contaminated digital source code that was infected with an arcane computer virus -- infested the logi-stacks and cogitator (computer) archives of the Mechanicum, causing literal Chaos to emerge in any cogitator system that was networked to one of its infected counterparts.The fabricator-general and his Dark Mechanicum allies used this disruption to marshal the strength of their forces, intent on bringing the rule of Mars firmly under their control. Infected by this vicious scrap code, the Titans of the Legio Agravides and the Legio Fortidus met their end when their reactors went critical and exploded, destroying their fortresses and eliminating these once-proud Titan Orders from the roster of Loyalist forces. In later years, this night would become known in Mechanicum legends as the "Death of Innocence."Later histories would record that the first blow of the Martian civil war was struck against Magos Mattias Kefra, whose forge city in the Sinus Sabaeus region was housed within the Madler Crater. Titans of the Legio Magna marched from the southern Noachis region and within solar minutes had smashed down the gates of Kefra's forge.Howling engines daubed in red, orange, yellow and black, decorated with flaming horned skull devices, ran amok within the high walls of the crater, crushing everything living beneath them and destroying thousands of standard years of accumulated wisdom in a fury of fire. Vast libraries burned and weapon shops that served the Imperial Army troops of the Solar Guard were reduced to molten slag as the indiscriminate slaughter continued long into the night, the Legio Magna's trumpeting warhorns sounding like the atavistic screams of primitive savages.Amid the Athabasca Valles, the war machines of the Legio Ignatum and the Burning Stars Titan Legion fought in bloody close quarters through the teardrop landforms caused by catastrophic flooding in an earlier, ancient age of the Red Planet. Neither force could gain the advantage, nor could either claim victory, so after a night's undignified scrapping, both withdrew to lick their wounds.Along the borders of the Lunae Palus and Arcadia regions, what previously had been simply a heated debate between the partisans of the Emperor and Horus erupted into outright civil warfare as Princeps Ulriche of the Death Stalkers unleashed his war engines upon the fortress of Maxen Vledig's Legio Honorum.Caught by surprise, the Legio Honorum lost nineteen Titans in the first solar hour of battle, before withdrawing into the frozen wastes of the Mare Boreum and seeking refuge in the dune fields of Olympia Undae. Their calls for reinforcement went unanswered, for all of Mars was tearing itself apart as the plague of civil war spread across the planet in a raging firestorm, a conflict known as the Schism of Mars by later generations.The fabricator-general's betrayal had only begun to unfold, and would soon see the Dark Mechanicum and the Traitor Titans of Mars joining Horus in open war against the Emperor on Terra itself.