Stygia-Aquilon

The infamous, binary worlds of fire and ice, Stygia-Aquilon are locked in perpetual orbit around one another, ellipsing around a giant, slowly-dying sun. The system is located on the Imperium's fringes along the desolate void-wastes to the galactic south-southwest, between the borders of the Segmentum Tempestus and the Segmentum Pacificus.

Since the closing years of the 37th Millenium, both worlds had been the territory of the brutal Executioners Space Marine Chapter. Their fortress-monastery was a huge armoured asteroid base known as the Darkenvault which is gravitationally trapped in the Lagrange point between these two worlds. It was from this bleak and foreboding bastion that the Executioners' skull-prowed warships sallied forth into the galaxy in search of targets to destroy.

That was, until a debt of honor compelled the Executioners to side with the Secessionists during the Badab War. After that conflict they were judged by the Imperium and ordered to undertake a hundred-standard-year-long Penitent Crusade during which they could not take in any Aspirants to replace their losses. The Executioners' twin Chapter worlds were given over in trust to the Salamanders Chapter and their own Successors rather than forfeited entirely, to be returned to them should they endure their hundred standard years of contrition and survive. Their future survival or destruction was left then in their own hands, subject only to the grace of the Emperor.