Even before the outbreak of open warfare during the Horus Heresy, the political climate on Mars, the sacred homeworld of the Adeptus Mechanicus was one filled with tension. There were unconfirmed suspicions that the Titan Legions stationed there had already secretly chosen sides in case of a potential conflict. At the outset of the Horus Heresy when the great Schism of Mars occurred, the Death Stalkers Titan Legion fought against the forces of the Loyalist Mechanicus. At the end of the Heresy the Death Stalkers were driven towards the Eye of Terror along with the rest of the Forces of Chaos. They remain trapped in servitude to the Chaos Gods, fighting the Long War that began ten millennia before.