5th Black Crusade

Abaddon the Despoiler launched his 5th Black Crusade in 723.M36, one of his infamous incursions into the realms of the Imperium of Mankind. He scoured the Elysia Sector, raiding hundreds of worlds and causing untold death and destruction. On Tarinth, the Despoiler lured the Warhawks and Venerators Chapters into the ruins of Kasyr Lutein where he traps them between the daemonic hordes of Khorne and the forces of the Black Legion. In a bitter last stand, both Loyalist Chapters were utterly destroyed, their skulls taken by the ancient Daemon Prince Doombreed, whose existence precedes that of the Imperium itself, to be mounted upon the mighty throne of Khorne.

History
The Fifth Black Crusade included among its many atrocities the scouring of the Elysia Sector, culminating in the destruction of the ancient Imperial city of Kasr Lutien. The Warmaster purposefully fomented invasions on a dozen worlds within the sector, entrusting the destruction of cities, shrines and temples to his warlords while using his fleet to keep the Imperial Navy’s Battlefleet Obscurus engaged in deep void skirmishes. It was Abaddon’s intention to create a sector-wide conflict that would provoke a massive response from the Imperium and draw in Chapters of the Adeptus Astartes. His plans set in motion, the Warmaster led the bulk of his Black Legion to the city of Kasr Lutien on Tarinth, burning the great city to the ground and enslaving its people.

When the Warhawks and Venerators Space Marines arrived on Tarinth in Chapter-size strength, they made an immediate assault upon Kasyr Lutien. At the same moment, Abaddon ordered the mass sacrifice of ten million Imperial citizens. Their blood funnelled via the city's great canals into a vast lake of gore. Above the lake, a rift into the Warp cracked open and Doombreed stepped into reality, howling in triumph. Abaddon had made a dark pact with Doombreed, promising it the skulls of an entire Chapter of Space Marines in return for its service. With thousands of Bloodletters pouring forth from the lake of blood, Doombreed waded into the ranks of the Warhawks and Venerators. The Black Legion then sprang their own trap, and from prepared positions across the city, they opened fire on the Loyalists, blocking their retreat. Though they fought without fear or respite, both Chapters fell that day, their warriors mutilated by the daemonic host and their gene-seed forever lost to the Imperium. The skulls of the fallen Space Marines were taken by Doombreed to be mounted upon the mighty throne of the Blood God.