Gerstahl was an Imperial Shrine World of the Adeptus Ministorum located in the Segmentum Obscurus near the Cadian Gate. Gerstahl had long been a place of peace and tranquility, 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 the Despoiler 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 as a Living Saint.
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