Astra Militarum - 13th Black Crusade and the Fall of Cadia: The Fortress World of Cadia had been the linchpin in the Imperium's defence against Traitor forces raiding from the Eye of Terror Warp rift for nigh-on ten thousand standard years. Standing guard over the critical Cadian Gate region, the planet and its soldiers symbolised stoic duty against horrific odds, their inviolability embedded in the wider Imperial Guard's consciousness as a key part of their identity.It was immediately before the opening of the Great Rift, at the culmination of Abaddon the Despoiler's 13th Black Crusade, that Cadia fell at last to the forces of Chaos.The planet had provided the Imperium with a cast-iron stronghold from which Astra Militarum campaigns had, for millennia, taken the fight to Heretic fleets, Chaos Cult uprisings and Daemonic incursions. It had held fast against multiple invasions by Traitors, mutants and even the monstrously powerful transhumans of the Heretic Astartes. Each attempt to conquer Cadia had been repulsed, though at increasingly immense cost to the regiments that defended its bastions, star forts, trench lines and bunkers. Abaddon's 13th Black Crusade, however, unleashed Chaos-worshipping Heretics in numbers not seen since the Horus Heresy.Under a sustained assault, the Astra Militarum on Cadia endured as Abaddon poured more and more of his seemingly limitless forces into crushing the world that for so long had defied him. Thunderous artillery bombardments pounded the invaders. Massed tank divisions duelled with Renegade armour formations through city outskirts. The regiments of the Cadian Shock Troops grimly held defensive positions, and the world's most elite troops -- the Kasrkin -- launched precision strikes against the Heretics, while other Imperial forces musted to repel the Archenemy's advances.The rallying cry of "Cadia Stands!" was taken up by Imperial Guardsmen and heard amongst the fortified kasrs of Cadia and elsewhere -- the term "kasr" being applied to both Cadia's own militariised cities and to some of its fortress-like sister planets in the wider Cadian System.No greater symbol was there of this will to push the Heretics back than Ursarkar E. Creed, the Lord Castellan of Cadia.Formerly the colonel of the Cadian 8th Regiment, Creed was granted overwhelming authority as the governing Lord Castellan of Cadia after a gross betrayal resulted in the assassination of Cadian High Command at the Battle of the Tyranok Fields. Creed later led the defenders' stand from the fortress-city of Kasr Kraf. His foresight to reinforce the defences of Cadia and to transmit ceaseless astropathic calls for aid bought a little time. Countless regiments of guardsmen -- amongst them many of Cadia's own lauded Shock Troops -- as well as forces of the Adeptus Astartes and Orders Militant of the Adepta Sororitas, flooded the Fortress World.Despite these reinforcements, the defence was not enough. At the campaign's zenith of bloodshed, Abaddon sent a sabotaged Blackstone Fortress he had originally captured from the Imperium during the Gothic War, the Will of Eternity, plummeting from orbit into Cadia's war-wracked surface. The colossal and ancient xenos void station's  impact would prove to be the final death blow for Cadia, and its inexorable approach through the atmosphere was like that of a burning comet. Creed vowed to remain in the wake of its impact, leading a rearguard action to enable as many survivors as possible to escape the doomed world.When the ancient void station struck the Fortress World, continents cracked; firestorms, tsunamis and hurricanes scoured the surface as the world's death throes were seismically triggered. The Warp, held back for so long by the Necrons' ancient Cadian Pylons, finally and greedily enveloped Cadia, anything that still lived on the planet's surface becoming a plaything for Daemons.Of nearly a billion souls who had stood to defend Cadia in the name of the Emperor, scarcely three million were evacuated off-world. Lord Castellan Ursarkar E. Creed and the remnants of the Cadian 8th -- the "Lord Castellan's Own" -- were not among them.