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A map of the Imperium of Man after ca. 999.M41 displaying the Great Rift and the Imperium Nihilus beyond; note the Nachmund Gauntlet in the galactic west near the Eye of Terror.

The Imperium Nihilus (pronounced NAI-hill-us), also known as the Dark Imperium in Low Gothic, was the name given to the half of the Imperium of Man isolated from Terra after the formation of the Great Rift, the so-called Cicatrix Maledictum, during the climax of the 13th Black Crusade in 999.M41.

The Imperium Nihilus encompasses most of the Segmentum Obscurus and Segmentum Ultima in the northern and eastern reaches of the galaxy, and was a defining feature of the astrography of the Milky Way Galaxy during the period known as the Era Indomitus.

The Dark Imperium was well-named, for beyond the Great Rift, the light of the Astronomican was obscured to the sight of Navigators and the Immaterium was roiled by the waxing might of the Ruinous Powers, making faster-than-light travel and astropathic communication extremely difficult, if not impossible.

The other half of Imperial space, where the light of the Astronomican was restored relatively soon after the end of the Noctis Aeterna, and was stabilised by the efforts of the first phase of Roboute Guilliman's Indomitus Crusade, was known as the Imperium Sanctus.



The Milky Way Galaxy in the Era Indomitus, divided into the Imperium Sanctus and the Imperium Nihilus by the Great Rift.

Thousands of worlds trapped within the territory of the Dark Imperium, such as Baal, the Chapter homeworld of the Blood Angels Space Marines, came under renewed assault from the myriad enemies of the Emperor of Mankind, including the forces of Chaos and xenos like the Tyranids, Orks and Drukhari, the dark Aeldari kin.

Such was the turmoil during the creation of the Great Rift and the period of the Blackness following it that there could be no reliable accounts of all that transpired in the territory of the Imperium Nihilus.

As limited communications returned, Historitors and Chronotechs struggled to understand incoming reports. With the influx of Warp energies into such vast regions of realspace, time passed strangely, speeding up in some sectors, slowing in others compared to the sidereal time experienced on Terra, at the heart of the Imperium.

These effects on the Warp from the birth of the Great Rift faded with the passage of time, allowing for the reestablishing of interstellar communications with some regions and somewhat more reliable Warp travel. This restoration of stability, combined with the onset of the Imperial counteroffensive known as the Indomitus Crusade led by the resurrected Lord Commander of the Imperium Roboute Guilliman through the first standard century of the 42nd Millennium, restored the grip of the Emperor over the Imperium once more.

However, the price paid proved steep. Slightly less than half of the one thousand Space Marine Chapters known to operate across the galaxy remained unaccounted for, and no less than twelve Space Marine Chapter homeworlds were reported as destroyed during the Noctis Aeterna and the equally bitter campaigns that followed.

Travel from the Imperium across the Great Rift into the Imperium Nihilus was extremely hazardous, and considered nigh-impossible, though the Indomitus Crusade Fleet Primus found a path through to come to the aid of the Blood Angels during the Devastation of Baal.

There was only one known passage -- the Nachmund Gauntlet. The Cicatrix Maledictum had at least one gap in realspace, although others were reported but not confirmed. The passage was near the Eye of Terror, which had been avoided by Navigators since the Great Crusade, for Warp Storms and strange anomalies had always made the region too dangerous to travel.

There, when the swirling nebula lulled, was revealed the Nachmund System, near to Agripinaa on the near side of the rift. Its Tyrant King, Kaligius, ruled over House Mandrakor, a household of Renegade Knights based on the Knight World of Dharrovar that had not been seen since the Horus Heresy.

Claiming Old Night had returned to plague the galaxy once more, Kaligius rejected communications from the Imperium, instead making pacts with Renegades and pirate fleets. Some Imperial starships have run the Nachmund Gauntlet successfully, but many more have been destroyed attempting the journey -- the ruined hulks of innumerable craft hang suspended in space as a vast voidship graveyard.

In the wake of the Devastation of Baal and the defeat of Hive Fleet Leviathan by the forces of the Blood Angels and the Indomitus Crusade, Guilliman declared that Lord Commander Dante, the Chapter Master of the Blood Angels, would serve as the Regent of the Imperium Nihilus while he concentrated on defending and strengthening the Imperium Sanctus on the other side of the Great Rift.

Life in the Imperium Nihilus


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

Vast tracts of Imperial space lie beyond the roiling Warp storms that make up the Great Rift. Cut off from all but the most determined aid, blind to the Astronomican's light and beset upon all sifes by legions of nightmarish foes, the worlds of the Imperium Nihilus, the "Dark Imperium," must look to their own survival, by whatever horrific means necessary.

The region of space known as the Imperium Nihilus is cut off from Terra's light by the Warp storms of the Great Rift. Not only is the light of the Astronomican obscured by these raging tempests, but there are also only two comparatively stable channels through which Imperial fleets are able to cross the storm front. Even these shuddering gauntlets are haunted by empyric phantasms and piratical wolf packs, but they are at least safer than the narrow passages that open sporadically between the storm belts only to sweep shut like a monster's jaws upon those brave or desperate enough to dare the crossing.

Thus severed from the rest of the Emperor's realm, each world in the Imperium Nihilus must stand alone amidst the darkness. Many fell during the first nightmarish days of the Noctis Aeterna, when shock waves of psychic upheaval lashed the galaxy in the wake of the rift's opening. Planets and their populations were annihilated or twisted beyond recognition as Warp storms engulfed them. Hordes of Daemons spilled from rents in the fabric of reality to butcher and torment all before them. Heretical cults arose, prophesying the end of all things and whipping formerly loyal citizens into a murderous frenzy. Rampant mutation ran rife, abominations were spawned from the darkest nightmares of Human minds and entire populations turned on one another in self-destructive storms of violence and cannibalism.

Other Imperial worlds held out. Fortresses rallied their garrisons, readied their weapons and drove back attackers from within and without. Hardy Agri-worlders formed defence militias, vanishing into the wilds and fighting guerilla wars against alien invaders. Industrial Worlds drafted every man, woman and child to churn out endless streams of materiel, hurling wave upon wave of conscripted soldiery into the teeth of terrors from beyond the stars.

Even still, for many worlds death might have been the kinder fate. The Immaterium roils and churns, making Warp travel catastrophically perilous. Forced to wrestle with spiteful empyric tides, wildly erratic destination flux and dramatic temporal distortion, Imperial voidships in the Imperium Nihilus can risk only the shortest Warp jumps, meaning that not only is travel through the Imperium Nihilus terrifyingly dangerous, but it must also proceed at a virtual crawl. Interplanetary communication, too, has been almost entirely stifled; forcing an astrotelepathic message across the Imperium Nihilus requires herculean and often fatal effort, and even those missives that do make it to their intended recipients arrive in the form of recurring nightmares.

Many worlds are wholly isolated, more than one population believing themselves the only surviving bastion of Human ciilisation in the galaxy. Many planetary governors, military commanders and religious leaders have been forced to make terrible choices and commit monstrous deeds in order to keep the lights of civilisation burning upon the worlds they rule. Plagues of mutation, madness and supernatural disease blossom while landscapes warp and change beneath baleful skies. Malefic entities manifest seemingly at will to prey upon the unwary, while simple despair stalks every Human soul. And always the Great Rift blazons itself across the firmament, corrupting all that its noxious light touches.

Though the Human territories within the Imperium Nihilus are crippled, the same is not true of their enemies. Some xenos species possess alternate methods -- be they technological, biological or seemingly sorcerous -- by which they can traverse the stars while bypassing the Warp altogether. Others revel in the madness that has been unleashed, joyriding the currents of empyric madness wherever fate wills and falling in howling tides upon whatever worlds lie in their path.

That which blights Imperial worlds, fleets and armies serves only to aid the worshippers of the Dark Gods. Even as it churns in madness, the Warp sweeps these Heretics and Traitors along on favourable tides, more often than not bearing them to their destinations swiftly, if not safely. Surges of immaterial energies allow renegade psykers to enact unspeakable rituals that drag entire worlds into damnation or translocate them into the hellish heart of the Warp. Ancient and terrible beings not seen abroad in millennia feed off the raw energies of unbridled chaos, gathering the strength to force their way through the veil and fall upon Humanity with howls of glee. Everywhere hope fails.

Still the Loyalist worlds of the Imperium Nihilus fight on, shoring up their faltering hope with unbridled hate. For every star system swallowed by the darkness, a crusade blazes a trail across the stars to relieve the desperate defence of another. Space Marine Chapter planets, Inquisitorial fortresses and Adepta Sororitas preceptories shine as bright beacons of defiance amidst the shadows. Knight Worlds light their watch fires and weather the storm, just as they did during the dread millennia of Old Night.

Meanwhile, daring Rogue Traders, dogged Adeptus Mechanicus Explorator fleets and courageous Imperial Navy flotillas brave the tumult of the Immaterium to bring hope to lost worlds or claim new colonies for Mankind. Perhaps the end of the galaxy draws nigh. Perhaps the darkness of the Imperium Nihilus will spread like a funeral shroud over all of Humanity's endeavours. However, while faith continues to burn strong in the hearts of men and women, the defenders of the Imperium will not give in.

Notable Sectors of the Imperium Nihilus

  • Finial Sector

Notable Worlds of the Imperium Nihilus

  • Dimmamar
  • Piscina


Also See


  • Dark Imperium (Novel) by Guy Haley
  • Codex Adeptus Astartes - Blood Angels (8th Edition), pg. 23, "Hope from Horror"
  • Warhammer Community - The Dark Imperium
  • Warhammer 40,000: New Heroes for a Dark Imperium
  • Imperium Nihilus - Vigilus Defiant (8th Edition), pg. 11
  • Warhammer 40,000: Rulebook (8th Edition), pp. 50-53, 123, 134, 152, 164-166
  • Warhammer 40,000: Core Book (9th Edition), pp. 22-23
  • White Dwarf 40 (December 2019), "Worlds of Warhammer" by Phil Kelly, pg. 11
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Warhammer 40,000 Overview Grim Dark Lore Teaser TrailerPart 1: ExodusPart 2: The Golden AgePart 3: Old NightPart 4: Rise of the EmperorPart 5: UnityPart 6: Lords of MarsPart 7: The Machine GodPart 8: ImperiumPart 9: The Fall of the AeldariPart 10: Gods and DaemonsPart 11: Great Crusade BeginsPart 12: The Son of StrifePart 13: Lost and FoundPart 14: A Thousand SonsPart 15: Bearer of the WordPart 16: The Perfect CityPart 17: Triumph at UllanorPart 18: Return to TerraPart 19: Council of NikaeaPart 20: Serpent in the GardenPart 21: Horus FallingPart 22: TraitorsPart 23: Folly of MagnusPart 24: Dark GambitsPart 25: HeresyPart 26: Flight of the EisensteinPart 27: MassacrePart 28: Requiem for a DreamPart 29: The SiegePart 30: Imperium InvictusPart 31: The Age of RebirthPart 32: The Rise of AbaddonPart 33: Saints and BeastsPart 34: InterregnumPart 35: Age of ApostasyPart 36: The Great DevourerPart 37: The Time of EndingPart 38: The 13th Black CrusadePart 39: ResurrectionPart 40: Indomitus