Segmentum Obscurus

The Segmentum Obscurus, also known as the Segmentum Obscura, is the region of Imperial space to the galactic north of Terra. This Segmentum of the Imperium of Man is the home of the vast permanent Warp Storm and Warp rift called the Eye of Terror, the primary base for the forces of Chaos in the Milky Way Galaxy. The Imperial Navy's Segmentum fleet headquarters is located in the Cypra Mundi System, which also serves as the central headquarters of the Imperial military's Segmentum Command.   The Segmentum Obscurus is the area of the Imperium most often under deadly threat by attacks from the Eye of Terror and is also the site for all of Abaddon the Despoiler's Black Crusades.   Since the creation of the Great Rift in the Era Indomitus, most of the Segmentum Obscurus now lies on the far side of the rift from Terra, and is part of the Imperium Nihilus where the light of the Astronomican no longer is easily visible.  

Notable Sectors:

Agripinaa Sector - The Agripinaa Sector is located close to the Eye of Terror. It was a major producer of military materials for Cadia and is still a linchpin in the overall defence of the remaining worlds of the Cadian Gate. In comparison to other Imperial sectors, it is a wealthy and prosperous area and produces many regiments for the Astra Militarum.   Cadian Sector - The Cadian Sector is the most heavily fortified sector in Imperial space, as it is the home of the Cadian Gate, the only clear route out of the Eye of Terror and into Imperial territory. The Fortress World of Cadia stood at the centre of the sector and its people served as the unflinching sentinels of the Cadian Gate. Cadia finally fell to the forces of Abaddon the Despoiler during the 13th Black Crusade in 999.M41, though a defence-in-depth was reconstructed around the hard-pressed remaining systems of the Cadian Gate.   Calixis Sector - The Calixis Sector is a sector of the Milky Way Galaxy that serves as the setting for the Dark Heresy role-playing game, which focuses on the actions of Imperial Inquisitors and their chosen Acolytes and Throne Agents. The Calixis Sector is located in the Segmentum Obscurus on the northern edge of the known galaxy, near the Halo Stars and the Eye of Terror. To the trailing edge of the galaxy, the Calixis Sector is bordered by the hazardous territories of the Fydae Great Cloud and to spinward by the Scarus Sector. Bordering to coreward, its immediate neighbour is the Ixaniad Sector. To rimward lie the contested and unregulated Imperial frontiers of the Halo Stars where humans and xenos mix in the quest for power and profit in the infamous Koronus Expanse. Conquered by Lord Militant Golgenna Angevin for the Imperium of Man almost two thousand standard years ago in the 39th Millennium during what became known as the Angevin Crusade, the Calixis Sector contains many heavily populated and important worlds, though it lies a great distance from the Imperium's core sectors. The sector's first Imperial Sector Governor was Drusus, one of Angevin's most capable generals, a man now revered as a Saint of the Imperial Cult.   Gothic Sector - The Gothic Sector is a sector of the Imperium of Man in the Segmentum Obscurus to the galactic north of Terra that is located on the border with the vast Ultima Segmentum. The Gothic Sector lies adjacent to the great Warp rift known as the Eye of Terror and was the location where Abaddon the Despoiler's 12th Black Crusade, colloquially remembered as the Gothic War, was fought from 139.M41 until 160.M41. The Forces of Chaos were defeated by the Imperium during that conflict, but Abaddon managed to seize several of the Blackstone Fortresses which he would use to achieve a more successful conclusion over 800 standard years later when he launched the 13th Black Crusade in 999.M41. The Gothic Sector and the Gothic War was also the setting for Games Workshop's tabletop game of starship combat, Battlefleet Gothic.   Ixaniad Sector - The Ixaniad Sector is ruled by several minor Highborn dynasties which lead their home planetary systems. These dynasties have battled each other throughout the millennia for dominance over the sector's politics. Fleeing refugees from these conflicts formed the original Meritech Clans in the border regions between the Ixaniad and Calixis Sectors. Other than its location and a few tidbits of information gained from its interaction with the more well-known sectors that surround it, very little else is currently known about the Ixaniad Sector in Imperial records.   The Koronus Expanse  -  Ts the name given by the authorities of the Imperium of Man to a dangerous unexplored region of the Halo Stars located beyond the Calixis Sector in the Segmentum Obscurus. The Expanse is accessed through the Koronus Passage, a treacherous but navigable route through the great Warp Storms that bar passage to the Halo Stars beyond the way station of Port Wander on the edge of the Expanse. The Expanse was untouched by the God-Emperor's Great Crusade many millennia ago -- and so it is a realm of fearsome xenos, treasures beyond imagining, heathen worlds of men, and the echoes of ancient doom.   Scarus Sector - The Scarus Sector is a division of the Segmentum Obscurus close to the Eye of Terror. Its sector capital is the Hive World of Eustis Majorus. The Scarus Sector borders the Calixis Sector to spinward and its known sub-sectors include Helican, Antimar, Angelus and Ophidian. This sector is the theatre of operation for the renowned Inquisitors Gregor Eisenhorn and Gideon Ravenor. The Helican Sub-sector is the site of the Helican Schism, a wave of rebellion, terrorism and sabotage that swept the area. The Ophidian Sub-sector is noted for being the site of the Ophidian Campaign (also known as the Purge Campaign), in which Battlefleet Scarus wrested control of the sub-sector from Heretic forces. The campaign lasted from 240.M41 to 337/338.M41 -- a considerable achievement in such a short timescale. Lately, the Scarus Sector has been plagued by invasions of Orks, who attacked en masse during the 13th Black Crusade and Greenskin infestation remains a very real problem in this corner of the Imperium of Man.