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The Segmentum Pacificus is the region of Imperial space that lies to the galactic west of Terra. The Imperial Navy fleet headquarters in the segmentum is located on the world of Hydraphur, which also serves as the segmentum fortress for the region.

This segmentum was made famous by the brilliant campaign of the great Lord Commander Solar Macharius and his conquest of a thousand worlds at the edge of the galaxy.

The Segmentum Pacificus was also a hub of activity during the Plague of Unbelief in the Age of Apostasy of the 36th Millennium when the Apostate Cardinal Bucharis sought to carve out his own empire several solar decades after the death of the Arch-heretic Goge Vandire.

The Segmentum Pacificus was also the site of the massive Sabbat Worlds Crusade unleashed by the Imperium of Man to retrieve the sector of the same name from domination by the forces of Chaos in the 41st Millennium.

Notable Regions


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

  • Veiled Region - This stellar region lies in, and to the galactic south of, the Segmentum Pacificus. This region of space is a vast, unmapped frontier zone that consists of dense nebulae and newborn stars. The region suffers from waves of intense stellar radiation being emitted by the new stars that coexists alongside discarded stellar matter. The entire region remains cloaked in stellar dust comprised of the light elements which form the building blocks of the new stars. This expanse of uncharted space serves as a home for several dangerous bands of Ork corsairs, various xenos mercenaries and a primitive, sluggish alien race of unknown name that resides on a dying planet. Unknown to the majority of the galaxy, the dreaded Necrons also inhabit this region of space. It was in the Veiled Regions that the notable Renegade Space Marine Chapter known as the Soul Drinkers temporarily sought refuge from Imperial forces.
  • Laanah Rifts - The Laanah Rifts is a region of the Segmentum Pacificus located in the northwestern fringes of the galaxy which was long held in the hands of aliens and Heretics, until the Imperium launched the Belrath Crusade in 182.M38. Within a century-and-a-half, a great swathe of the Laanah Rifts was brought under the dominion of the Imperium of Man, which contributed to the eventual founding of the Laanah Sector.

Notable Sectors

  • Chiros Sector - Located on the Segmentum's borders with the Segmentum Tempestus, the Chiros Sector is a turbulent frontier realm which encompasses sub-sectors from both Segmentae. The Chiros Sector saw a marked increase of military activity during the first half of the 41st Millennium. Due both to xenos incursions such as Aeldari-piracy and Ork-invasions, but also Chaos-led rebellions, the Chiros Sector is a realm in constant turmoil that needs increased vigilance if it is to prosper.
  • Sabbat Worlds - The Sabbat Worlds is the name given to a group of star systems that form the Sabbat Worlds Sector along the rimward edge of the Imperium of Man's Segmentum Pacificus. Made up of over 100 known star systems, the region is subdivided into several discrete territories, most notably the Newfound Trailing, the Khan Group, the Cabal Systems, the Carcaradon Cluster, and the Erinyes Group. It is rumoured that the Blood Pact, a highly organised Chaos warrior-cult devoted to the Blood God Khorne, originally came from a star system in this sector. First annexed for Imperial colonization in the 35th Millennium, the name Sabbat refers to the area's original redeemer, Saint Sabbat, a young girl who received a vision from the Emperor to lead a Crusade to bring the region into the Imperium during a Crusade that lasted for 105 standard years and began in 500.M35. Things became rapidly worse for the human population of the Sabbat Worlds during the 41st Millennium, however. A charismatic, brutal Archon rallied the tribes of the Sanguinary Worlds to war, and a series of assaults began from galactic trailward into the region. The assault was thought at first to be a return to the minor Chaos conflicts of the 38th Millennium in the region, but in the years following 600.M41, it became impossible to ignore the true threat presented by Chaos Undivided. The Ruinous Powers had decided to take the whole region away from the Imperium. The Imperium never intended to abandon the Sabbat Worlds, but the power and size of the attacking force was underestimated from the beginning, and the Imperial defenders initially stood little chance. Some held out for as long as a century, but by 740.M41, the Sabbat Worlds were fully in the hands of Chaos, and the area was reclassified "unstable/hazardous" by the Administratum. In the next year, 741.M41, the Civitas Imperialis, the centre of Imperial control in the region, was forced to remove itself from the Sabbat World of Khan Nobilis to a neighbouring sector of the Segmentum Pacificus, and the entire region was officially lost to Chaos. From that time unto the present day, an Imperial Crusade has been ongoing to free the Sabbat Worlds from the hands of the Archon who rules in the name of Chaos, and to reclaim this sector for the Golden Throne. Frightening losses have been suffered by the Imperial forces engaged in the Crusade, and the threat of the Archon's forces has proved to be a true danger to the Imperium of Man, but there is no reason to doubt that the forces of the Sabbat Worlds Crusade will ultimately succeed in restoring the light of the Emperor's peace to this region of the galaxy.
  • Laanah Sector - The Laanach Sector is the Imperial sector that emerged following the conquest in the 38th Millennium of the region of the Segmentum known as the Laanah Rifts.

Notable Worlds

  • Constantinium (Civilised World) - Formerly known as Nova Terra, this contested world is best known for having rebelled against the reign of the Imperium twice in its history during the age known as the Nova Terra Interregnum and the Constaninus Iconoclasm.
  • Hydraphur (Forge World/Segmentum Fortress) - This notable Forge World is the location of the main Imperial Navy Battlefleet Pacificus headquarters within the Segmentum Pacificus and also serves as the location of the Imperial military's Segmentum Command.
  • Macharia (Shrine World) - Homeworld of Lord Commander Solar Macharius and the site where he began his famous Macharian Crusade. Since his death, the Adeptus Ministorum has declared Macharius a Saint of the Imperial Cult and renamed his homeworld Macharia in his honour. This Shrine World attracts millions of visiting pilgrims.
  • Verghast (Hive World) - Located within the Sabbat Worlds Sector, during the Sabbat Worlds Crusade, the vitally important Hive City of Vervunhive came under siege from the neighboring hive of Ferrozoica. The Hive leadership's pleas for Imperial assistance were answered by a small task force, including the Tanith First and Only Imperial Guard regiment under the command of Commissar Ibram Gaunt. Soon after they landed, it became clear that Ferrozoica had also been corrupted by Chaos, which mobilised the entire hive population into a heretic army numbering several million strong. The Forces of Chaos were ultimately defeated on Verghast but at the high price of the loss of Vervunhive. Many of the Vervunhive survivors then joined the Tanith 1st Regiment to replace the losses suffered by the regiment which had sought to protect their home.

Notable Celestial Bodies

  • Halo Zone - The Halo Zone contains those 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. These Halo Stars are believed to be the oldest stars in the galaxy 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. This region of space lies beyond the light of the Astronomican, which is used by Imperial Navigators to guide vessels while traveling in the Warp. Without the guidance of this vital beacon, Navigators are unable to sense its guiding light and are forced to navigate blindly. Navigators often refuse to travel into this region for this very reason, for it is extremely hazardous to do so.



  • Codex: Chaos Space Marines (4th Edition), pp. 18-19
  • Codex: Eye of Terror (3rd Edition) pp. 10-11
  • Codex: Imperial Guard (3rd Edition, 1st Codex)
  • Codex: Imperial Guard (3rd Edition, 2nd Codex)
  • Codex: Sisters of Battle (2nd Edition), pp. 39-42
  • Codex: Space Wolves (2nd Edition)
  • Imperial Armour Volume Ten - The Badab War, Part Two, pp. 97-98
  • Rogue Trader: Core Rulebook (RPG), pp. 305-315
  • Warhammer 40,000 Rulebook (5th Edition), pp. 116, 124-125, 144
  • Hellforged (Soul Drinkers Novel Series) by Ben Counter
  • Necropolis (Novel) by Dan Abnett

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

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