The Segmentum Solar is the vast region of Imperial space centred on Terra and the Sol System. The Imperial Navy shipyards for the Segmentum are located on Luna, and the Imperial Navy headquarters in the Segmentum is based within Mars' Ring of Iron. The Segmentum Solar is the central hub of the Imperium of Man and the most ancient and densely settled region of human space. Centered on Terra, where the Emperor of Mankind sits upon his Golden Throne, the central Segmentum is protected on four sides by the other Segmentae Majoris. The Battlefleet Solar of the Imperial Navy is the largest of the Segmentae fleets and is based in the orbital fleet docks of the so-called Ring of Iron that surrounds the Adeptus Mechanicus' primary Forge World of Mars.
Donorian Sector - The Donorian Sector is home to several intelligent alien races, including the K'Nib and the Clawed Fiend.
Trail of Saint Evisser - The Trail of Saint Evisser is a collection of star systems located on the far western edge of the Segmentum Solar. This tract of frontier space was visited during the pilgrimage of an obscure Administratum officer named Kelkannis Evisser, who was mysteriously turned into an Imperial Saint. This region was so named because of the unwavering faith the saint brought to this collection of worlds in the wake of his visits.
Sol System - The Sol System, also known as the Terran System or Solar System, is the name given to the home solar system of Mankind in the Age of the Imperium. The system is named for its sun, Sol, and lies at the direct astrocartographic center of the Segmentum Solar. Its planets include Terra and Mars, the twin capitals of the Imperium. There are eight planets and many dwarf planets in the Sol System, some of which are also orbited by heavily settled moons, including Luna and Titan.
Terra (Hive World) - Terra is the throne world of the Imperium of Man and the original homeworld of Mankind and of the Emperor. It is the most sacred and revered place in all the million worlds that comprise the Imperium.
Luna (Dead World/Civilised World) - Luna is a densely settled Civilised World of the Imperium. Its massive population lives in great cities built deep below the lunar regolith. Luna is most famous for its gene-laboratories where the Emperor of Mankind made the genetic breakthroughs that would ultimately culminate in the creation of the Primarchs during the legendary Primarch Project of the late 30th Millennium.
Mars (Forge World) - Mars is the greatest Forge World of the Imperium of Man, producing vast numbers of weapons, vehicles and other technology for the Imperial war efforts throughout the galaxy.
Ceres - Ceres is a small dwarf planet located within the Sol System's inner astroid belt. During the Horus Heresy era, Ceres was home to relay and communication stations that helped with communications between the inner and outer reaches of the system.
Elysia - Elysia is the homeworld of the famed Elysian Drop Troops regiments of the Imperial Guard, a verdant Imperial Civilised World in the Segmentum Solar, some 30 light years from the Hive World of Armageddon. The Elysia System and the surrounding space were notorious havens for human and Eldar pirates. Because of this ever-present threat, the Elysian Planetary Defence Force (PDF) gained intensive experience in ship-to-ship combat and serving alongside naval support when attacking isolated space-based pirate outposts. The Elysian Drop Troop Regiments raised by the Imperial Tithe for service in the Imperial Guard are elite, all-volunteer units whose troops are required to first serve at least one tour of combat duty in the Elysian PDF before they are allowed to join.
Hermetica - Hermetica is a vitally important Hive World and capital of the Chonma Sector. In 659.M41, it came under a massive assault from a vast mutant horde numbering in the millions, led by the armies of the Word BearersDark Apostle Leyak the Devourer. Thanks to the intervention of both the ferocious MinotaursSpace MarineChapter and the Imperial Guard forces of nearby Necromunda, the heretic forces were defeated, though at great cost to the war-torn planet, which was left devastated in the wake of the brutal fighting. A Space Hulk, Nightmare of Paradox, utilised by the arriving Chaos army, still orbits the planet in a quarantined zone, awaiting the Grey Knights Chapter to come and examine the derelict vessel for possible daemonic infestation.
Molech - Molech was a verdant Knight World located only a few short light years from Terra itself. This world was ruled by the ancient noble family of House Devine. During the Dark Age of Technology, the Emperor was said to have traveled there on a one-way spacecraft, and found a gateway into the Realm of Chaos, where he made a devil's bargain with the Ruinous Powers. When he re-emerged into the material realm from the Immaterium, he had become imbued with new powers and the knowledge of how to created the genetically superior Primarchs. Molech was later brought into the fledgling Imperium during the Great Crusade in the 30th Millennium by the combined forces of the Dark Angels, Emperor's Children, Luna Wolves and White Scars Legions. Those who accompanied the Emperor, had their memories erased so that they did not know Molech's significance. The Emperor left a substantial Imperial presence behind to garrison the vitally important planet. The Knights of House Devine came to dominate Molech, becoming its rulers, and built the city of Lupercalia, in honour of Horus Lupercal, constructing the burgeoning city over the cave network where the Warp Gate was located. When the Horus Heresy began, Molech became the site of a major invasion by the traitorous Sons of Horus, led by Warmaster Horus himself, who had regained his lost memories of the planet, and wished to partake of the same journey his father had made millennia earlier. During the height of the fighting, House Devine turned rogue and helped the Traitors conquer the world in the Warmaster's name. Horus entered the Warp Gate and returned changed -- more powerful and nearly on par with the formidable powers of the Emperor Himself. At the conclusion of the Horus Heresy, during the Great Scouring, a combined strike force of Knights from Houses Cadmus, Terryn and Borgius, annihilates the turncoats of House Devine as Imperial forces reclaim Molech.
Necromunda - Necromunda is a vitally important Hive World located in the Imperium's Segmentum Solar, and a major producer of munitions for the Imperial Guard. Formerly known as Araneus Prime, it was first settled over 15,000 Terran years ago during the Dark Age of Technology as a mining and manufacturing colony. It was later rediscovered and forcibly brought into Imperial Compliance by the Imperial FistsLegion, but the destruction wrought during the campaign ravaged the planet's surface with unnatural fire, it world-city cracked and rendered to dust and ash. The Imperium gave the charred world a new name, one that echoed with a world brought to the threshold of death but one that still lived -- Necromunda.
Paramar V - Paramar V lies in the Paramar System at the outer northern edge of the Segmentum Solar. It was also lay in direct conjunction with the Istvaan System and Terra. Since the fourth decade of the Great Crusade, Paramar had stood both as a vital lynchpin of the Imperium for empyreal travel and as a staging post for outward expansion during that era. Paramar V was established is an important deep storage facility for supplies and munitions for ongoing Expeditionary Fleets. During the opening years of the Horus Heresy this planet was attacked, following the events of the Dropsite Massacre on Istvaan V, by a large Traitor force comprised of the Alpha Legion, Dark Mechanicum allies and the Titans of the Legio Fureans. During this conflict, which came to be known as the First Battle of Paramar, it was valiantly defended by the local Mechanicum forces, Thallaxii cohorts and Skitarii forces, and was further augmented by the unexpected arrival of the Loyalist Iron Warriors of the 77th Grand Battalion and Titans of the Legio Gryphonicus. But despite their best efforts, the world still fell to the Traitor assault. Paramar V would be the sight of two more battles -- one, which occurred later during the Heresy, and the final battle, when the planet was finally liberated during the Great Scouring.
Jupiter - Jupiter is a massive gas giant and is the fifth planet in the Sol System. The space docks and workshops that orbit Jupiter are home to massive Imperial Navy Shipyards controlled by the Tech Priests of Mars. During the time of the Horus Heresy, the moons of Jupiter were known to have habitats for the workers of the shipyards in Jupiter's orbit. It was here that infamous Word Bearers ship, the Furious Abyss, was constructed, before it turned its guns upon the Jupiter and destroyed its shipyards in order to maintain the secrecy of its existence.
Tentrion - Tentrion is a world of sprawling cities and manufactoria of prodigious output, a formerly long-abandoned remnant of the glory days of the Age of Technology. This world was the site of one of the earliest campaigns of the Great Crusade outside of the Sol System. Deemed vitally important, the Compliance of Trention was deemed a high priority by Imperial forces, who wished to use the industrious planet as a staging point to push the Emperor's Great Crusade outwards. Not wising to lose such a valuable world, the vast armies of both Terra and Mars was unleashed upon Tentrion, only to be met by the massed levies and towering autonomous gun platforms of the Pontifex of Tentrion. When all seemed lost, the Titans of the Legio Praesagius blasted the world's cities and slaughtered the soldiers sent against them, to cow them with the sheer destructive force of their Titans. In a five day long gruelling series of titanic duels with the multi-legged gun platforms of the Tentrion Pontifex, the Legio Praesagius established the Imperium's supremacy on the field of battle and proved its noble intent, and so, Tentrion joined the Emperor's realm as willing subjects.
Titan (Inquisition Fortress World/Space Marine Chapter Homeworld) - Titan is the largest moon of the gas giant Saturn in the Solar System and is wholly controlled by the Grey KnightsChapter of psychically-active Space Marines who serve as the Chamber Militant of the Inquisition's Ordo Malleus. The fortress-monastery of the Grey Knights is based on Titan, and is carved entirely of basalt. Within the fortress hang pennants, banners and flags commemorating the victories and sacrifices made by the Chapter in their eternal war against the daemons of Chaos, but none other than the Grey Knights would recognise the names of these campaigns. The Chapter operates in oppressive secrecy, beyond the knowledge of the Adeptus Terra and even of the Imperium of Man's ruling High Lords of Terra; as a part of the Ordo Malleus, the Grey Knights are answerable only to the Inquisitor Lords of the Ordo Malleus and the Emperor of Mankind himself. Even the location of the Grey Knights' fortress-monastery on Titan is known only to the Ordo Malleus. Titan itself is surrounded by the rings of Saturn and the other moons of the gas giant which are all highly-secret Inquisition-controlled worlds, including: Mimas, the prison and execution centre of the Ordo Malleus, Enceladus, the home of the most powerful Inquisitor Lords of the Ordo Malleus and other influential Inquisitors of that Ordo, and several other satellite worlds all dedicated to the secret task of confronting the corruption of Chaos across the galaxy.
Saturn - Saturn is a massive, ringed gas giant and the sixth planet of the Sol System. The moons of Saturn serve as the location for a massive complex of military bases and orbital shipyards run by the Inquisition. All of these areas are off-limits to anyone who does not serve or have clearance from the Ordos of the Inquisition.
Uranus - Uranus is a massive gas giant located in the Sol System. Though never habitable, it is home to orbiting Human colonies.
Venus- Venus is an inner planet of the Sol System. During the early stages of the Great Crusade, Venus was conquered by the Iron Warriors Space Marine Legion during the Mehr Yasht campaign.
Neptune - Neptune is a massive gas giant located in the Sol System. Neptune was first colonized by humanity during the time known as the Age of Terra. By the time the Emperor reconquered Neptune during the Great Crusade, its inhabitants had mutated into mutants, which caused them to be destroyed by the forces of the Emperor.
Pluto - Pluto is a small dwarf planet located in the outer most rim of the Sol System. During the Horus Heresy era, Pluto was home to relay stations that were responsible for warning Terra of any imminent invasion.
Sedna - Sedna was a planetoid sized trans-Neptunian object of xenos origin located within the Sol System's inner Oort Cloud. During the early Great Crusade eight Space Marine Legions fought against an unremembered xenos species on the dark surface of Sedna, finally leaving the entire Sol System in human hands for the first time since the start of the Age of Strife.
Necromunda (Hive World) - This Hive World is a major producer of munitions for the Imperial Guard and its vicious underhive gangs often serve as recruiting grounds for the Space Marines of fleet-oriented Chapters such as the Imperial Fists.
Farfallen (Former Paradise World) - A former Paradise World located in the Trail of Saint Evisser that has fallen into decline as the Trail began to deteriorate and the majority of the population in the region moved away. The planet's natural environment has begun to slowly reclaim much of the former civilised regions. The Adeptus Ministorum still maintain a Hall of Remembrance for the collection and compilation of the Trail's religious legacy for posterity.
Magnos Omicron (Forge World) - An Adeptus Mechanicus Forge World that continues to supply the Imperium with much-needed armoured vehicles and weapons, thus allowing this world to avoid much of the spiral of decay that has affected the majority of the Trail of Saint Evisser.
Solshen XIX (Agri-World) - This former Agri-World was the site of a horrific Ork invasion that killed most of the population. Among the survivors was Kelkannis Evisser, the Administratum Adept who went on to become a Saint of the Imperial Cult.
Sophano Secondus (Feudal World) - This Feudal World is ruled by a king known as the Allfather. The Inquisition discovered a Chaos Cult dedicated to the formidable Daemon Prince of Tzeentch named Ghargatuloth, the Prince of a Thousand Faces, within its capital city of Hadjisheim. This cult was led by the original Imperial missionary Crucien, who was over 1,200 standard years old as a result of the blessings of the Ruinous Powers.