Abaddon the Despoiler launched his 3rd Black Crusade in 909.M32, sending the Daemon Prince Tallomin against the Cadian Gate in a reckless and bloody frontal assault. The daemonic horde that followed in Tallomin's wake accounts for the destruction of millions of lives and draws in Imperial Guard regiments and Space Marine Chapters from across the Segmentum Obscurus.
Eventually, warriors of the Space Wolves manage to send Tallomin howling back into the Warp. Under the cover of the attack, Abaddon led a dedicated strike force to desecrate the Shrine World of Gerstahl, breaking the ancient seal on the tomb of the Imperial Saint Gerstahl and utterly destroying his remains whilst the Imperium's attention was directed elsewhere.
The Shrine World of Gerstahl had long been a place of peace and tranquility in the Segmentum Obscurus, its faithful offering their prayers daily to the God-Emperor. The planet was named for Saint Gerstahl, an Imperial Army officer who had fallen defending the Cadian Gate during the first centuries after the Horus Heresy. Entombed under the world's alabaster capital, the saint was prophesied to rise again when the "Eye of Darkness opened for the last time" and stem the tide of the treacherous.
When Abaddon launched his 3rd Black Crusade he attacked the Fortress World of Cadia, to distract the Imperium from his desecration of the saint's tomb in an attempt to forestall the saint's possible contribution to preventing the Imperium's collapse in the far future. With whispered lies and promises, Abaddon unleashed the Daemon Prince Tallomin, the so-called "Prince of Princes," against the Cadian Gate.
Abaddon had convinced the creature that the blood of the loyal Adeptus Astartes could grant him unheard-of-strength and the power to crush his daemonic rivals within the Eye of Terror. In a gore-soaked assault, Tallomin and his minions slew many millions of Imperial soldiers and lured no less than a dozen Loyalist Space Marine Chapters to battle.
In the end, the ferocious warriors of the Space Wolves finally drove the Daemon Prince screaming into the Immaterium, but Abaddon had already achieved his aim, destroying the remains of Saint Gerstahl and forestalling any chance of the prophecy's fulfillment.
- Black Legion: A Codex Chaos Space Marine Supplement (6th Edition) (Digital Edition), pg. 32
- Liber Chaotica: Khorne, pg. 84