Caldera

Caldera is an Imperial hive world and death world, known to the Great Crusade as One-Five-Four Four. Its human population descended from people of Nocturne freed from Dark Eldar captivity by craftworld Eldar, and the world was a rare example of coexistence between humans and Eldar until the Salamanders under Vulkan, with Ferrus Manus and Mortarion, brought it into compliance during the Great Crusade and Vulkan ordered it purged by fire. Vulkan briefly returned to Caldera during the Horus Heresy while seeking a passage to Terra. During the War of the Beast he reappeared there to defend it almost alone against an Ork invasion, and with Imperial forces under Koorland he prevented its conversion into an Attack Moon.