- "Silent in the Calixian extent are worlds from which the Omnissiah has withdrawn His blessings. They trail their parent stars like errant children struck dumb and bloodied. Their ruins are profound, their catacombs endless, their savages sorrowful - for these wards of the Imperium of Mankind have paid a great and terrible price for the tech-heresy of their forbearers."
- — Warrus the Secondmost, Indexus Astrae Calixis
A Hell-Forge is a fallen Forge World dedicated wholly to the Ruinous Powers and controlled by the Dark Mechanicus. Most of these Hell-Forges lie in the Eye of Terror located in the Segmentum Obscurus or the Hadex Anomaly in the Jericho Reach. These infernal forges of the fallen scions of the Cult Mechanicus burn with the terrible smells of burning blood and scorched flesh, fed by souls as well as Promethium and steel, constantly churning out arms, armament and Daemon Engines for their Dark Mechanicus lords and their Traitor Legion allies. The ubiquitous holy symbol of the blessed cogwheel, the Cog Mechanicum, is gone; replaced by leering metal skulls set in a circlet of spiked teeth. Within these foul realms there is no proper, logistical structure to the world. Forge-cities rise in random fashion, lurching towards the skies and deep into the planetary crust at the whim of their dark lords. To the Adeptus Mechanicus, these Hell-Forges are a dark mirror of their own holy Forge Worlds, one they dare not contemplate too closely.
There are those servants of Chaos who live beyond the normal ken of mortals within a realm not entirely of the material universe and not entirely of the Warp: a Daemon World where the laws of nature and reason have been completely usurped by the whims of the Ruinous Powers. Here daemons roam freely and are constantly nourished by the twisting winds of sorcery as mortals become their playthings with a value only as Chaos Champions or slaves. Daemon Worlds are a sanctuary for the worshippers of Chaos with the means and courage to flee to them. The Inquisition never rests in its efforts to eliminate the devotees of the Dark Gods, but a Daemon World defies even their shadowy reach.
A few Daemon Worlds are dominated by the remnants of the Dark Mechanicus that once followed Horus. These Dark Mechanicus Hell-Forge worlds are wholly given over to daemon-machines and infernal industries, where mills grind flesh and suffering is the currency used to make the insane visions of their nightmarish masters real. Countless millions are enslaved to work in a world-spanning network of labyrinthine forges, churning out an endless supply of weapons and armaments for the Traitor Legions' Long War against the Imperium. The masters of these Dark Mechanicus Hell-Forge worlds, most now half-daemonic machines themselves, have long since left the shreds of their humanity behind and are beholden to none -- be they mortal or Chaos God. They sell or barter their unholy inventions and arms to the highest bidder, be they warlord, demagogue, Chaos Sorcerer or Daemon Prince without favour, and their coin of exchange is always the same -- new raw materials -- the flesh and souls of slaves for the Dark Forge World's unquenchable hunger.
These fallen Forge Worlds are enclosed in a perpetual blanket of dark grey clouds. Below the clouds is the source: stack after stack of vertical pipes rising even to the lower cloud decks and billowing thick smoke into the acrid air. No sign of the actual surface can be seen, for all is covered with layered factories, which are burning, creating, and forging night and day (though there are few who can tell the two apart given the atmosphere). Robed figures wander without wasteful delay in their tasks, exposed cloth allowing glimpses of artful mechadendrites or metallic limbs. Closer examination reveals more of the real nature of these dark worlds. Unhidden, clear to even a casual glance, is the mark of the Ruinous Powers. Runes and glyphs of unholy meaning litter walls, declaring patronage to the Dark Gods. Even the Hereteks carry these marks upon their branded flesh, their allegiance to the Machine God burned away from their synapses. The forges themselves burn with the terrible smells of burning blood and scorched flesh, fed by souls as well as Promethium and low-gravity alloys of steel. The blessed Cog Mechanicum is gone, instead there are leering metal skulls in a circlet of spiked teeth. But the worst thing is that there is no proper, logical structure to the world. Forge cities rise in random fashion, lurching towards the skies and deep into the planetary crust at the whims of their Dark Magi lords.
- Xana II - The oldest reference to the Hell-Forge of Xana II appears in the introduction to the final volume of the writings of the cursed Heretic archivist of the Gethsemane Reclusium, purporting to catalogue certain terrors that lurk within the Eye of Terror beyond the ken or mortal savant and beyond the reach of even the keenest of assassin's blades. Xana II seems to be the source of several classes of Attack Craft frequently utilised in the armies of the Great Enemy, the most notorious of which are the Hell Blade and the Hell Talon. While Xana II itself is located within the baleful energies of the Eye of Terror, craft matching the description of the Hell Blade and Hell Talon have been sighted in war zones across the galaxy, suggesting that its masters -- themselves known to be singular hybrids of man, machine and Daemon -- have established bonds with factions across the void and are supplying them with weapons and materiel to further their own ends. To date, the greatest concentration of Attack Craft Imperial forces have faced was at the infamous Siege of Vraks, but recent confessions extracted from captured Hereteks suggest a mustering of unprecedented scale beyond the Cadian Gate.
- Retlaxi - The name of this ancient fief of the Mechanicum of old was thought long consigned to history. Yet in the manner of so many things damned by the stain of the Warp, it resurges periodically to instil doubt and fear in the souls of the faithful. Having lain dormant for the better part of eight Terran centuries, the name has appeared once more in at least a dozen confirmed remote prognostications, several readings of the Emperor's Tarot and at least one recorded communion with a ritually summoned and bound ætheric entity. The world was once a subject of the Traitor Collegia Titanicus Legio Mortis, and so it is the Imperium's greatest concern that its foundries, if still they function, may be supplying arms and ammunition to this Arch-Traitor body.
- The Silent Forge - The matter of the appearance of the Daemon Engines codified as Decimators has been the subject of several previous conjunctions, and the majority of the Inquisition are agreed that the source of these vile hybrids of machine, Daemon and xenos artifice lies beyond the Laanah Rifts in the region known to the Imperium as the Silent Abyss. Having gathered together a number of transcriptions of post-mortem confessions extracted by way of the Thanatos Protocols, Inquisitors are now certain that the long outlawed Hereteks of the Sepktraal Cult are in contact with the source of the Decimators, which they apparently know as the Silent Forge. Furthermore, these transcriptions link several Renegade Adeptus Astartes warbands to the Silent Forge, suggesting that the Sepktraal are serving in the capacity of brokers, facilitating the armies of the Great Enemy and gaining the services of these mighty engines of war. What the Silent Forge demands in return, or what share of that price the emissaries of the Sepktraal claim can only be guessed at, but no doubt speak to the very depths of sin and blasphemy.
- Abheilūng - Survivors of the mission group dispatched to the Abheilūng System have recently returned, reporting that Abheilūng, which lies on the vital Armageddon-Paramar Grand Conduit, is lost to the Imperium. They reported that elements of the Dark Mechanicus laired beneath the surface of the world, and have employed forbidden rites of techno-pyroclasm to cause the dormant volcanoes to erupt as one, sealing the death of millions in a single moment. Worse was to come, however, for out from the roiling black clouds and rivers of molten rock charged an uncountable host of Daemon Engines. It is estimated that the entire population of Abheilūng has now fallen to the Dark Mechanicus, slaughtered, consumed or dragged beneath the ground in fetters to rend the infernal forges below. It is many Inquisitors' beliefs that Abheilūng is now entirely in the hands of the Dark Mechanicus that must have lurked unseen in its volcanic labyrinths for so long, and while the admission is likely that Abheilūng is already on the path to becoming a significant locus of production of infernal engines of war and that soon the Traitor Legions and others will be able to procure the services of machines wrought in its forges.
- Cyclotrathe - A former manufactory world known to the Imperium only by the most ancient texts, the name Cyclotrathe was long ago purged by umbra-net data-phages by order of the highest possible authority. This minor Forge World was located in the Coronid Deeps within the Imperium to the galactic east of the Cyclops Cluster. This Forge World was one of many worlds that were a part of the sovereign domain of the Mechanicum, known as the Cyclothrathine Holdfast. Born not of ancient history, but rather some of the darkest and most horrifying conflicts of the Great Crusade and long withdrawn into secret ways and the study of the arcane, they were recognised by their strange arachnid symbol and their robes not of Martian crimson, but of deepest hearts-blood and sable, and by the fathomless storm-cloud hues which adorned their servants and engines of war. For years they had garnered a reputation for ruthlessness and aggression, both in defence of their domains from any xenos that crossed the frontier, and in pressing any claims they made to resource rights and territory. Imperial law and the intercession of Mars had been called upon on more than once occasion to keep Cyclothrathe's expansion in check. Bellicose and arrogant, the black-clad Magi of Cyclothrathe kept their distance even from others of their own kind, and where they walked, they walked alone. During the Horus Heresy, the Warmaster Horus played on the jealousy and ambition of the Cyclothrathine Mechanicum to whom Mars was at best an unwanted and distant authority. Though considered a minor Forge World at the time, it brought other, more unique powers into the Traitors' fold. In return, the Warmaster offered the Cyclothrathe freedom; no ultimate master but himself as a disinterested overlord who did not care to interfere with their works, their creed or where their arts led them, so long as his rule remained unopposed and his warriors were glutted with arms. The Warmaster offered the black-clad Magi an empire; a domain of their own to rule in his name, and for years their vault-fanes and sunken forges laboured in secret and without the knowledge of the Imperium nor of Mars, fashioning baroque engines of destruction and unliving legions of Battle-automata, stockpiling them in the deep vaults beneath their lightning-scoured world, waiting for the trumpet of war to call them forth. The future would decide for this world an infamy seldom matched in the ranks of Forge Worlds. It is many Inquisitors' beliefs that certain factions amongst their outcast kin in league with fallen adepts of the machine have recently established contact with the Traitors of Cyclothrathe, returned to threaten the northern marches of the Segmentum Solar as they did so many long millennia ago.
- Samech - The former Adeptus Mechanicus domain of Samech stands as a dire warning of weakness, for its lords were not sufficiently strong of will or spirit to rein in those powers they were forced to utilise when their world was cut off from the Emperor's grace by Warp Storm activity. Some would take their example as a warning against consulting forbidden archives in time of need, others against doing so without having taken the proper precautions. During the region's Age of Shadows, when Warp Storms cut the Jericho Reach off from an Imperium preoccupied with more pressing concerns, world after world fell to darkness and disorder in a slow descent that marked the once proud Imperial sector's collapse into decay. For many planets, the fall was a slow one, a mere footnote for later Imperial scholars to document as the sector became a lawless Reach. However, for one planet there is an occurrence that the Adeptus Mechanicus will let none forget, when what was once a firm bastion of the Cult Mechanicus treacherously fired upon a formally recognised Explorator fleet. For followers of the Machine God, this simple act is a declaration of utter rebellion for Samech, and enough for them to forever seek its destruction. The truth was far worse, for the Omnissiah's light had been slowly dimming on the Forge World for some centuries before the infamous event. When the Hadex Anomaly consumed the world in Warp energies many Terran years later, the forges were ready to seek out the Ruinous Powers to further their own aims, as well as alien races and archeotech sources previously prohibited by Mars. Samech now stands as the main source of armaments used against the Imperial forces in the Acheros Salient of the Jericho Reach, creating profane combinations of authorized Imperial technologies, unconsecrated archeotech, unholy creations of Chaos, and even the inhuman workings of the xenos. These abominations represent the real nature of Samech -- a world where nothing is forbidden when it will garner influence and stature, of brokers willing to deal with anyone or anything as long as payment is made, of agents ever searching for undiscovered technologies to exploit. There is no morality other than the ruthless quest for power and survival in the war-torn Jericho Reach.
- Uraniborg 1572 - Recent reports indicate that the Adeptus Mechanicus domain of Uraniborg 1572 has fallen from the grace of the Emperor, its foundries turned to the production of the tools of damnation at the behest of Traitor Magi and the status of its attendant Titan Legion the Legio Serpentes -- unknown. It is the Inquisition's belief that, given current commitments in that region, and the continued uncertainty regarding the fate or loyalty of the Legio Serpentes, Uraniborg 1572 is, to all intents and purposes, lost to the Imperium.
- Temporia - The name Temporia appears in but a handful of archives, all of them penned by the hands of Heretics long ago consigned to the pyre. To name such a place is to invite into the soul a portion of the madness and unreality in which it is steeped, and in doing court the damnation so many haven to. In his vision, the captive Warp-seer known as the Oracle of Brass decribes an impossible realm of cogs and arcane mechanisms the size of continents and mountain ranges that can only relate to a Hell-Forge dedicated to the Ruinous Power known as the Changer of The Ways. Further assayances have served to solidify the Inquisition's view that Temporia is a Hell-Forge entirely in the sway of that power and that it exists, at least partially, deep within the heart of the Eye of Terror. This gargantuan mechanism turns in patterns mortals cannot, and should not, fathom, for they can only serve the cause of their destruction and ruination.
- Sarum - Several of the accounts of the Great Crusade that the Inquisition has unique access to make mention of the machine domain of Sarum, though they provide scant details save that the airless planetoid was home to an aberrant order of machine adepts and was the site of an overwhelming assault by the World Eaters Legion of the Legiones Astartes. Having collated numerous texts on the subject of this world, Inquisitorial savants have uncovered a link between it and a number of void clanner legends long told throughout the Golgothan Wastes. Though each story differs in many regards, they all appear to describe a wandering planetoid which is home to a crimson-clad order of hell-smiths whose faces are dominated by lamprey maws lined with razor-sharp steel teeth. It is not known if the long-lost machine realm of Sarum was subjected to some unknown Warp phenomenon that has caused it to manifest at different times and places across the Golgothan Wastes and potentially beyond. While outlandish, such events are far from unknown to the Inquisition. Furthermore, in assaying these tales that the Warp Ghosts are able to predict or even cause manifestations of this ethereal Hell-Forge, acting as some form of dread ferrymen as they steer the long-damned foundries across the wastes and bring death and destruction upon the heads of those who dwell near the void along the coreward borders of the Segmentum Solar.
- Crucible-Omega - Certain lords of the Inquisition have long posited the existence of a domain of the fallen Mechanicus beyond the boundaries of the Imperium's realms, some believing it a Forge World long predating the Age of Strife which was never contacted during the Great Crusade. Various legends have surfaced of a world of crippled hell-smiths that prostrated themselves before a cyclopean machine altar sending up venerations in sonorous binaric cant that echoes weirdly through the Empyrean and can be perceived by the Inquisition's Warp-seers when the tides of the Sea of Souls rage especially strong. The Inquisition have recently learned of a Phaenonite cell whose unhallowed master believes Crucible-Omega to be very real indeed, and that the altar its population worships is in fact a functional Standard Template Construct (STC) system.
- Antioc - Located in the Prath Veil Sub-sector of an unknown sector of the Segmentum Obscurus, the Forge World of Antioc was captured by the Forces of Chaos during an incursion from the Prath Nebula. It is currently lost to the Imperium and has become another Hell-Forge of the Dark Mechanicum.
- Incaladion - A former Loyalist Forge World located in the Ultima Segmentum, Incaladion was the homeworld of the Legio Fureans (Tiger Eyes) Titan Legion before the outbreak of the Horus Heresy. The Incaladine adapted to their savage world accordingly. They acquired additional human stock by raiding the feral populations of the world, which brought echoes of barbarous and macabre cultures that began to infect the increasingly schismatic Machine Cult propagated by the Incaladine Mechanicum. With the outbreak of the Heresy they declared for the Warmaster Horus. This world was cleansed by Loyalist forces during the Great Scouring.
- Deathwatch: The Achilus Assault (RPG), pp. 89-94
- Deathwatch: The First Founding (RPG), pg. 94
- Imperial Armour Volume Thirteen - War Machines of the Lost and the Damned, pp. 12-13
- Imperial Armour Volume One - Imperial Guard and Imperial Navy, pg. 8
- The Horus Heresy - Book One: Betrayal by Alan Bligh, pp. 99-101
- The Horus Heresy - Book Three: Extermination by Alan Bligh, pp. 154-157
- The Horus Heresy - Book Four: Conquest by Alan Bligh, pp. 52-63, 76