Legio Tempestus - Horus Heresy: The events that unfolded on Mars solar decades after Cavalerio's return to the Red Planet, formed a crucial fulcrum in the Warmaster Horus' conspiracy to unmake that which the Emperor had built during the Great Crusade.During the 31st Millennium the climate on Mars was one of great discontent. There were tense relations between the various magi with sporadic outbreaks of espionage and violence being committed amongst the 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.Princeps Senioris Cavalerio sought to keep his Legio free from the insidious poison of the Mechanicum's politicking. He believed that the Titan Legions should remain true to their warrior ideals and not be instruments of the magi's political will, and serve only the interests of the Imperium of Man itself. During the Great Crusade the Legio Tempestus supported Primarch Roboute Guilliman's Ultramarines Legion.Shortly before the outbreak of the Horus Heresy, the Legio took part in the Epsiloid Binary Cluster Campaign, during which the Titan of Princeps Cavalerio was damaged, forcing him to leave the bulk of the Legio Tempestus under the command of Princeps Maximus Karania and join the detachment of war engines headed to Mars for repairs. Princeps Cavalerio was scheduled to remain on Mars until all of his Titans were fit to return to combat.When the Schism of Mars began during the opening days of the Horus Heresy the Legio Mortis forces, led by Princeps Camulos in the towering Imperator-class Titan Aquila Ignis, moved to threaten the Legio Tempestus stronghold at Ascraeus Mons. The Death's Heads trespassed on Legio Tempestus territory, violating an agreement signed between the two rival Titan Legions several centuries prior.Although the Legio Tempestus had the right to open fire on the offending war engines, Princeps Cavalerio dared not do so, as his forces stood no chance against the awesome power of the Imperator Titan, and he was also unwilling to be the one to start a shooting war between brother Titans on the surface of Mars.A stand off between the two forces occurred in front of the Ascraeus Chasmata, and although not a single shot had been fired, the Legio Tempestus war engines were struck by a scrapcode (computer virus) attack that caused the death of a number of Legio Tempestus personnel aboard the Titans, as well as destroyed Cavalerio's Titan, the Victorix Magna. Following this assault, the Legio Mortis retreated from Legio Tempestus territory.As a result of the death of his Titan, Cavalerio had to be interred in an amniotic tank, which required a period of psychological adjustment to become comfortable with his new existence. During this time, Cavalerio was deemed unfit to command the Legion, and Princeps Kel Sharaq assumed his duties as acting Princeps Senioris of the Legio Tempestus on Mars.Princeps Cavalerio slowly recovered while the conflict on the surface of Mars escalated, and although Princeps Sharaq received numerous petitions from Mechanicus forge cities asking the Legio Tempestus to intervene, he acceded to none, as he believed that such an order should come only from the Stormlord himself.Facing the Legio's gravest crisis in its long and glorious history, Princeps Senioris Cavalerio felt that warriors of honour and courage should not stand idly by in such times, but act. He assembled his princeps and proclaimed to them that the Legio Tempestus would go to war, with him in command of the Legion's first god-machine, the Deus Tempestus.The Legio Tempestus sallied forth in support of Magma City, a Loyalist forge that stood in defiance of the newly imposed order of the corrupt Fabricator-General Kelbor-Hal and his Dark Mechanicum co-conspirators.The forces of the Legio Tempestus stood firm in the face of aggression in the defence of their allies, though they knew they would find their inevitable doom at the hands of their hated rivals in the Legio Mortis.The Legio Tempestus was overwhelmed by the superior numbers and firepower of their rivals. Despite the odds, the Stormlord valiantly led his Legio in the destruction of the Death's Heads' lesser war machines, only to face his own destruction, along with the remainder of his own war engines, at the hands of the Imperator-class Titan Aquila Ignis.The heroic deeds performed in that final battle will never be fully honoured, for most who witnessed them perished themselves as Magma City sunk into the Red Planet's savage fiery mantle.After the tragedy on Mars, there remained only a scattered handful of Loyalist Legio Tempestus Titan maniples and detachments who had not been present on the Red Planet, free and in the Imperium's service, but left leaderless and bereft, and soon to face the double blow of the news that their distant brothers had themselves turned Traitor.While leading his own division of the Legio Tempestus, Karania proved himself a strategist whose cunning served as a formidable force multiplier and elevated the Legio to the highest tiers of the Warmaster's servants. This rise in favour, however, was ever checked, for its oldest foe, the Legio Mortis, remained of all the Traitor Titan Legions always first in Horus' service.Despite their common cause in the ranks of the arch-Traitor, Tempestus and Mortis, long rivals, slowly became bitterest enemies even as they fought alongside each other, a diametrical opposition that would at length become horribly evident as the unspeakable powers each had sworn themselves to exerted their hideous influence.There are no records of the Legio Tempestus engaging in any further actions during the remainder of the Horus Heresy, though it is presumed they continued to fight on.At some point in its later history, the traitorous elements of the Legio Tempestus (now referred to as the Legio Tempestor) were present during the Siege of Terra, but when the Warmaster fell, they were driven towards the Eye of Terror along with the rest of the Traitor Legions during the era known as the Great Scouring.There they remain, trapped in servitude to the Chaos Gods, fighting the Long War against the "Corpse Emperor" that began ten millennia before.The Legio Tempestor 's current whereabouts are unknown. The Loyalist Legio Tempestus was later relocated to the Forge World of Orestes, located in the Segmentum Pacificus.Its most recent action was participation in the Sabbat Worlds Crusade in the 41st Millennium, to which its homeworld contributed much war materiel by virtue of its close proximity to the theatre.The Sabbat Worlds Crusade Warmaster's constant requests for supplies and the support of the Legio Tempestus drained the world of resources and left it weak -- rendering it a perfect target for Archon Urlock Gaur, the commander of the forces of Chaos in the Sabbat Worlds Sector.When the attack finally came, Orestes was saved only due to the support of the Legio Invicta, which was passing nearby on its way to join the forces of the crusade on the Sabbat front.