Orpheus Sector - The Horus Heresy: When the Imperium was torn apart by the civil war that followed the Warmaster Horus' betrayal, the Orpheus Sector was largely abandoned to its fate, as neither Loyalists nor Traitors displayed much interest in this far-flung region of space during the conflict. Those xenos domains not yet eradicated by the forces of the Great Crusade surged forward and the Dark Marches quickly became a lawless borderland where renegades and xenos corsairs roamed freely. Only the Imperial outpost on Amarah Prime continued to enjoy some measure of stability, but it would not last indefinitely.Somewhere during the first century of the 31st Millennium, a Traitor warlord by the name of Dynat Mal -- originally belonging to the Alpha Legion -- chose the Dark Marches as a safe haven to escape the press of those armies loyal to the Emperor which had launched a new crusade known as the Great Scouring. Having gathered a thousand strong coterie of Renegades, Heretics and diabolists around him, Dynat Mal's warband took the name of The Shadowed Ones and destroyed the Imperial outpost on Amarah Prime, plundering its stores and stockpiles after having massacred the outpost's entire population. Several punitive expeditions launched by the reemerging Imperium were destroyed through the use of guerilla tactics and the baleful powers of Chaos.With the destruction of the outpost on Amarah, any Imperial claim to the region was effectively severed. Yet the Imperium could not so easily let a known foe roam its borders freely. The Raven Guard Chapter still sought to avenge the deaths of their fellow Legionaries during the Battle of Lyx, for which Dynat Mal was responsible. Around the year 170.M32, the Raven Guard despatched a sizeable taskforce under Captain Kallengier to bring Dynat "Crowbane" Mal to justice.Yet, despite intensive search and reconnaissance, the Alpha Legion still eluded the vengeful Raven Guard until the task force reached the heart of the Orpheus Sector. There, in the deep jungles of the world of Apollyon, the Raven Guard Astartes discovered the broken hull of a Strike Cruiser quickly identified as the Occam's Razor, known to have belonged to the XX Legion's fleet. While the Strike Cruiser's demise could not be ascertained for sure, the surroundings of the broken warship were still more unsettling -- like a grim tombstone or grave marker, the Occam's Razor stood over a valley filled with the bones of the dead.The corpses mostly belonged to mutated humans but also to the Aeldari, to the Khrave and to several other unidentified xenos forms. Most disturbing of all, however, were the sundered warplates of the Astartes which not only bore the colours of the Alpha Legion, but also those of the White Scars and the Iron Hands. The identity of the perpetrator of the massacre remained unclear and the Raven Guard did not linger long, for their Librarians’ visions told of an impending doom should they remain at the site. Their vengeance denied once more, the Raven Guard departed the baleful valley, their questions unanswered.In the millennia that followed, the Dark Marches were utterly neglected by the Imperial authorities and left to fend for themselves. Very few facts can be verified about what occurred in the region during this period as the Segmentum Tempestus is frequently isolated by powerful Warp Storms and other stellar phenomena. It is only in the wake of the Age of Apostasy that the eye of the Imperium once again rested on those worlds that would soon become the Orpheus Sector.