Sebastus IV

Sebastus IV is a world recorded in Horus Heresy-era chronicles as the site of the Iron Cage, an Iron Warriors prison-fortress. Raised in the aftermath of the Drop Site Massacre at Isstvan V, it held Imperial Fists survivors of that betrayal, confined within iron cages suspended in sight of one another so that each captive’s slow death by starvation and exposure became a spectacle for the rest. The atrocity gave the site its name and fixed Sebastus IV permanently in the memory of the Imperial Fists Legion and its Successor Chapters.

Among those held there was Captain Darnath Lysander, later a legendary figure of the Imperial Fists Chapter, whose lasting hatred of the Iron Warriors is traced by tradition to his imprisonment in the Iron Cage. Imperial Fists memory treats the episode less as a defeat in battle than as a betrayal of honourable war, ranked alongside the Isstvan V massacre as evidence of the Iron Warriors’ descent into cruelty during the Warmaster’s rebellion. Sebastus IV is attested chiefly through this single, defining incident; no continuous campaign history, garrison, or planetary governance accompanies it in the record.

No confirmed account places Sebastus IV within the Imperium’s later administration, the Scouring that followed the Heresy’s end, or the present era beyond its standing as the origin of Lysander’s enduring grudge. Its galactic coordinates are not fixed in any record consulted here, and the world remains, for now, a name bound to a single Heresy-era event rather than an ongoing presence in the timeline. It endures nonetheless as one of the formative sites in the long enmity between the Imperial Fists and the Iron Warriors.