Warhammer 40k Wiki
Warhammer 40k Wiki

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.

As such, it currently is home to the majority of the Imperium's armed forces, which were most recently mobilised to a state of readiness not seen since the Horus Heresy as a result of the 13th Black Crusade in 999.M41.

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[]


The galaxy in the Era Indomitus in the wake of the birth of the Great Rift.

  • 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.
  • Athena Sector - Prior to the Gothic War (ca. 140.M41), patrol ships in the Athena Sector discovered Imperial vessels, including an Emperor-class Battleship, drifting uncontrolled through Wilderness Space. Boarding parties found the crews killed by disease, and Xebal Astolax, Magos Biologis of the Adeptus Mechanicus, examined corpses from the merchant vessel Shanxi, identifying symptoms of the disease. Inquisitor Horst learned that rumours that the ancient Murder-class Cruiser Plagueclaw, crewed by followers of Nurgle, was active were spreading among captains of the Imperial Navy. Watch posts near the Cadian Gate were put on heightened alert and Battlefleet Cadia was reinforced.
  • 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.
  • 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.
  • 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.

Notable Systems[]

  • Agripinaa System - The Agripinaa System lies within the wealthy and prosperous Agripinaa Sector, located close to the Eye of Terror. Comprised of eight planets, this vital system was a major producer of military materials for Cadia and was a linchpin in the overall defence of the Cadian Gate. Following the destruction of Cadia at the hands of Abaddon the Despoiler, this system has become a haven for Cadian refugees that have taken refuge upon the world of Chaeros, which has since been renamed New Cadia.
  • Belis Corona System - The Belis Corona System is a system of Imperial space located within the Belis Corona Sector near the neighboring systems of the Cadian and Agripinaa Systems.
  • Belial System - The Belial System was a system of Imperial space located to the northeastern region of the Cadian Gate. It was home to the planet of Belial IV, a former Aeldari homeworld that was pulled towards the Eye of Terror during the Fall of the Eldar and became a Crone World, deserted and abandoned.
  • Chinchare System - The Chinchare System is a rogue system comprised of nearly a dozen worlds. During the 13th Black Crusade, the beleaguered forces of the Imperium found themselves unexpectedly assaulted by the sudden materialisation of Aeldari forces throughout the sub-sector.
  • Dhobash System - The Dhobash System is a system of Imperial space comprised of five worlds that was devastated by the massive incursion of the Forces of Chaos during Invasion of the Stygius Sector during the 13th Black Crusade.
  • Gildar System - The Gildar System is a star system in the Segmentum Obscurus of the Milky Way Galaxy and it possesses an astonishing wealth of natural resources. The system consists of eight worlds, most of them uninhabited. The Silver Skulls Space Marine Chapter considers the system to be a part of their territory and no Imperial starship can travel through the area without their permission or escort. The world of Gildar Secundus was the site of a vicious battle between the Silver Skulls and the Red Corsairs Renegade Space Marines for control of the region known as the Gildar Rift. The Silver Skulls proved victorious and drove the Red Corsairs from the system, but at a very high cost. The Captain of the Silver Skulls' 4th Battle Company, Daerys Arrun, was slain in close combat by the Red Corsairs' infamous Chaos Lord, Huron Blackheart.
  • Hydra Cordatus System - The Hydra Cordatus System was home to the desert Forge World of Hydra Cordatus located in the Segmentum Obscurus near the Eye of Terror. It was one of the few locations in the galaxy where the Adeptus Mechanicus stored its tithes of Space Marine gene-seed, in this case of the genetic material drawn from the Imperial Fists Chapter.
  • Kharon System - The Kharon System is a system of Imperial space located in the Segmentum Obscurus.
  • Khravos System - The Khravos System is a system of Imperial space that was devastated by the massive incursion of the Forces of Chaos during the Invasion of the Stygius Sector.
  • Mordian System - The Mordian System is a system of Imperial space that was devastated by the massive incursion of the Forces of Chaos during the Invasion of the Stygius Sector. This system is home to the famous Mordian Iron Guard regiments of the Astra Militarum.
  • Prismata System - The Prismata System is a system of Imperial space that was devastated by the massive incursion of the Forces of Chaos during the Invasion of the Stygius Sector.
  • Salamar System - The Salamar System is a system of Imperial space that was devastated by the massive incursion of the Forces of Chaos during the Invasion of the Stygius Sector.
  • Thracian Primaris System - The Thracian Primaris System is a part of the Helican Sub-sector, a notable sub-sector of the Scarus Sector.
  • Urtek System - The Urtek System is a system of Imperial space that was devastated by the massive incursion of the Forces of Chaos during the Invasion of the Stygius Sector.

Notable Worlds[]

  • Agripinaa (Forge World) - Agripinaa, known as the "Orb of a Million Scars," is a notable Adeptus Mechanicus Forge World located in the Agripinaa Sector. This world primarily provided materials for the Cadian front and its industrial heartland is solely engaged in the production of ammunition. Located near the Eye of Terror and assaulted by the Chaos forces of Abaddon the Despoiler during the 13th Black Crusade, Agripinaa did not weather the attacks of the Forces of Chaos well and much of its industrial heartland was laid to waste.
  • Belial IV (Crone World) - The world of Belial IV was one of the early Aeldari Maiden Worlds, but when it was pulled towards the Eye of Terror during the Fall of the Aeldari, it became a deserted and abandoned Crone World. It is said to be home to a sacred Aeldari artefact of black crystal, one of the Crone Swords forged from the energies of death now desperately sought by the Ynnari.
  • Belis Corona (Dead World / Segmentum Battlefleet Headquarters) - Belis Corona is an Imperial Dead World located near the Eye of Terror, which serves as the Segmentum Obscurus' primary base for the Imperial Navy's Battlefleet Obscurus as well as the Imperium's administrative capital for the entire Segmentum. There is a vast conglomeration of orbital dockyards in geosynchronous orbit about Belis Corona where entire sector battlefleets can be serviced and refitted. Massive stockpiles of munitions, supplies and other war materiel are stored in armoured bunkers buried many kilometres below the planet's barren surface.
  • Cadia (Fortress World) - Cadia, officially known as Cadia Prime, was a terrestrial, Earth-like planet that has been classified as both a Civilised World and as the Imperium of Man's most important Fortress World by the Administratum. It guards the only known navigable route to and from the massive Warp rift known as the Eye of Terror, a passage called the Cadian Gate. The world's dangerous proximity to the Eye of Terror made it necessary for the people of Cadia to heavily fortify the planet. Cadia was always the first target of the Chaos Warmaster Abaddon the Despoiler's assaults and Black Crusades, when the Forces of Chaos Undivided launched themselves from the Eye of Terror every few centuries in an attempt to break out and invade the Imperium proper as they did during the Horus Heresy. Cadia's natural environment was much like Terra's was millennia ago, with a large ocean covering 70 percent of the planet's surface. The land mass that did exist was divided between incredibly thick pine forests and vast glaciers. The planet was slightly cooler than most human-settled worlds but not to the point that it adversely affected growing conditions. Settled before the onset of the Age of Strife by a branch of humanity that eventually fell to the worship of the Chaos Gods and played a major role in the ultimate corruption of the Space Marine Legions, Cadia was re-settled sometime in the early 32nd Millennium by Loyalist humans of the Imperium. The world's landscape was dotted by strange black pylons of clear xenos origin called the Cadian Pylons. These devices were actually constructed by the Necrons millions of Terran years ago to hold back the psychic energies of the Eye of Terror from the world, which was an ancient Necron military base during their war with the Old Ones. The Cadian Pylons and other similar devices on worlds in the region were what created the unusual area of realspace stability known as the Cadian Gate near the Eye of Terror that is unaffected by the constant Warp Storms that surround that Warp rift. Cadia's location directly adjacent to the dangerous Eye of Terror has made it necessary for the people of Cadia to fortify the planet to an extent where almost the entire population lives in massive fortress-cities known locally as "Kasr". Thus Cadia has an odd mix of dense urban areas and vast open tundras and other natural landscapes. During the 13th Black Crusade in 999.M41, Cadia finally fell to the assault of Abaddon the Despoiler. Only a few million managed to flee off-world before it was consumed by the energies of the expanding Eye of Terror. Many of these refugees made their way to the Agripinaa System's world of Chaeros, which was renamed New Cadia.
  • Chinchare (Mining World) - An asteroid locked in a figure of eight orbit around a binary star. It was once home to a creature of Chaos formed from the coagulated bodies of pilgrims who had descended into the asteroid to worship a corrupted crystal structure known as the Lith. The creature was later destroyed by Inquisitor Gregor Eisenhorn and Magos Geard Bure. This asteroid possesses a wealth of ultra-rare metals such as ancylitum and phorydnum, and supported a workforce of almost 3,000 miners and associated staff. During the 13th Black Crusade, contact with this isolated world was lost. Its current status is unknown.
  • Fenris (Death World) - Fenris is the Death World in the Segmentum Obscurus that is the homeworld and recruiting ground for the Space Wolves Space Marines Chapter and of their Primarch Leman Russ. Fenris takes its name from the mythical Norse wolf fathered by the god of tricksters Loki that would assault the Norse gods during the Final Battle of Raganarok. Most of the names of locations on Fenris are also drawn from the Norse mythology and languages of Old Earth. Fenris is situated in the galactic south of the Segmentum Obscurus, at the end of the Warp rift known as the Eye of Terror, from which come the Forces of Chaos to raid and pillage. Fenris thus lies at the forefront of the Imperium's defence against Chaos. The Space Wolves maintain the vigil that began many millennia ago at the close of the Horus Heresy and watch over a hundred other worlds besides. Their domain stretches far and wide across the scattered stars that girdle the Fenrisian star system, but it is the bitterly cold Death World at its heart that the Space Wolves proudly call home.
  • Hydra Cordatus (Forge World / Desert World) - An Imperial Forge World and Desert World located near the Eye of Terror, it is one of the few locations in the galaxy where the Adeptus Mechanicus stored its tithes of Space Marine gene-seed, in this case of the genetic material drawn from the Imperial Fists Chapter. The planet consisted of only a spaceport and a single large citadel and manufactorum complex known as the Tor Christo. The Tor Christo was a large star-shaped fortress connected to a smaller half-star fortress built into the side of a nearby mountain. The citadel had a large garrison of Imperial Guard troops and even a small Titan Legion to protect its precious contents. During the 13th Black Crusade, this world was assaulted by a large Iron Warriors warband, who successfully defeated the defending Adeptus Mechanicus forces and small Imperial Fists garrison stationed there. When they finally departed, they stole the gene-seed stored within the Tor Christo, a devastating blow to the Imperial Fists, but an insult which would not go unavenged.
  • Medusa (Feral World) - Medusa is the Chapter homeworld of the Iron Hands Chapter of Space Marines. The world of Medusa is a harsh realm of perpetual gloom, situated precariously close to the Eye of Terror in the Segmentum Obscurus. The sun almost never breaks through the dark and polluted sky, as it constantly churns over a land of frozen mountain ranges, interspersed with volcanoes and boiling hot geysers. The landscape is under constant flux, the shifting of tectonic plates forming new mountains and seas, and destroying them as quickly as they are created.
  • Mordian (Hive World) - Mordian is an Imperial Hive World in the Segmentum Obscurus that is the homeworld of the Imperial Guard's Mordian Iron Guard Regiments. Many of the Imperium's enemies have underestimated these ranks of colorfully-uniformed troops, only to find out that they are among the toughest and most uncompromising of the Emperor's soldiers. The people of Mordian are often of a dour and grim temperament, living as they do in perpetual darkness. The suicide rate on the planet is reportedly now the highest in the Imperium since the destruction of the Night Lords Traitor Legion's homeworld of Nostramo. Mordian also once came under a great assault by the forces of Chaos that was defeated only through the extraordinary discipline and valour of the Iron Guard in one of the Imperium's finest moments. Mordian is tidally locked with its star, so that the Mordian day is the same as the Mordian year. As the planet rotates exactly once for every orbit around the sun, one-half of the planet is bathed in perpetual darkness and the other half burnt to a cinder by the glaring sun. This unusual planetological characteristic makes Mordian a truly miserable world to live upon. The planet's lack of rotation prevents any strong winds from developing due to the lack of a Coriolis Effect and as such the atmosphere is thick and dark. The world's billions of human inhabitants live in vast hive cities where all resources are controlled and distributed by the Mordian state. There is much discontent among the people, and the Imperial Guard Regiments raised from Mordian, the Mordian Iron Guard, spend much of their time simply keeping the populace in line when they are not deployed to Imperial war zones.
  • Scintilla (Hive World) - Scintilla is the capital world of the Calixis Sector of the Segmentum Obscurus, and is a thriving Imperial hub that supports the largest planetary population in the sector. It is dominated (some observers say “shared") by two vast hive cities, Hive Sibellus and Hive Tarsus, into which the vast majority of the planet’s groaning population are crammed. Despite the dominance of the two great hives, the “offspring” communities of Ambulon and Gunmetal City contribute significantly to the planet’s economic function. Scintilla is a world of splendours where the wealthy and powerful compete with ruthless appetite. Astonishing magnificence abounds, from the wondrous fashions of the hive nobility to the towering spectacle of the hives themselves. Landmarks like the Lucid Palace and the Cathedral of Illumination are famous throughout the sector.
  • Vostroya (Industrial Hive World) - Vostroya is an Imperial industrial Hive World in the Halo Zone of the Segmentum Obscurus, located beyond the Eye of Terror. The planet is considered an "Industrial World" by the Imperium of Man, because it does not quite meet the legally defined requirements to be considered an Adeptus Mechanicus-ruled Forge World, but it is not quite like an independently-governed Imperial Hive World either. Like all Forge Worlds, Vostroya has deep ties with the Adeptus Mechanicus, but because it is not ruled entirely by the Priesthood of Mars, it is not classified as one of their worlds. The origins of this unusual arrangement can be found in the Age of Strife, when Vostroya was the rare independent world that swore allegiance to Mars, rather than be settled by a colony of Tech-priests as was the norm for almost all of the other Forge Worlds. After declaring its allegiance to the Mechanicus, Vostroya quickly developed into a heavily industrialised world with the influx of Mechanicus personnel and technological knowledge. Under Imperial rule, the output of the many Vostroyan manufactorums now provide war materiel for the Emperor of Mankind's massive war machine.

Notable Celestial Bodies[]

  • Blackshine Nebula - The Blackshine Nebula is a stellar body located in the Calixis Sector.
  • Halo Stars - The Halo Stars are the ancient stars that encircle the outer edge of the Milky Way Galaxy, representing the last stellar clusters to be encountered before one enters the eternal, frigid night of the intergalactic void. The Halo Stars are believed to be the oldest stars in the Milky Way and their circumference extends for approximately 200,000 light years around the galaxy, usually grouped in a cluster formation. The Halo Stars may also be intermixed into the shroud of dark matter that is known to extend beyond the visible disk of the galaxy for several hundred thousand light years. The Halo Stars are older than most can understand, and are characterised by mystery and danger. The Halo Stars have remained largely unexplored by the Imperium of Man and it is unknown what kind of habitable worlds, if any, may circle them. The Halo Stars have a very bad reputation amongst Imperial starfarers and it is believed by many, including quite a few Rogue Traders and Adeptus Mechanicus Explorators, that those foolish enough to venture out into the Halo Stars never return. During his crusade, Lord Commander Solar Macharius led forces into the edge of the Halo Zone where the light of the Astronomican faded, but they ultimately refused to go further. The Koronus Expanse is an area of the Halo Stars adjacent to the Calixis Sector in the Segmentum Obscurus that has begun to be explored by agents of the Imperium in the 41st Millennium, led by the fleets of various Rogue Traders.


  • Battlefleet Gothic Rulebook, pp. 92-102, 158-159
  • Codex: Eye of Terror (3rd Edition)
  • Codex: Imperial Guard (3rd Edition, 1st Codex), pg. 23, rear cover
  • Codex: Imperial Guard (5th Edition)
  • Dark Heresy (Core Rulebook)
  • Index Astartes II, "Wolves of Fenris - The Space Wolves Space Marine Chapter"
  • Index Astartes III, "Hand of Justice - The Iron Hands Space Marine Chapter"
  • Rogue Trader: Rulebook (RPG), pp. 315-316
  • The Inquisition (Background Book)
  • Warhammer 40,000: Rulebook (5th Edition), pp. 116-117, 138
  • Warhammer 40,000: Rulebook (8th Edition), pg. 53, 160-165
  • White Dwarf 139 (US), "Space Fleet: Rules Expansion", pp. 8-36
  • White Dwarf 140 (US), "Space Fleet: Additional Background, Rules, Data Cards & Counters", pp. 46-75
  • The First Heretic (Horus Heresy Novel) by Aaron Dembski-Bowden
  • Ravenor (Novel) by Dan Abnett
  • Fantasy Flight Games, Scarus Sector Map

Segmentum of the Known Galaxy
Segmentum Solar Segmentum Ultima Segmentum Tempestus Segmentum Obscurus Segmentum Pacificus