The rebel Forge World of Moirae from which the heresy that afflicted the Mechanicus spread was destroyed by a retaliatory Exterminatus action carried out by the Martian Mechanicus, but not before its heretical creed split the wider Adeptus Mechanicus in two.
The ensuing conflict drew Titan Legions and even those Space Marine Chapters affiliated with the Adeptus Mechanicus into the turmoil. The schism took a heavy toll on the Adeptus Astartes, resulting in the destruction of dozens of Space Marine companies and the excommunication of several Iron Hands clan companies, which went on to found the Sons of Medusa Chapter.
It took over two Terran millennia of desperate warfare before the Moirate doctrines were considered fully purged from the servants of the Machine God.
Nova Terra Interregnum
During the early years of the 35th Millennium, the Imperium was divided in half after the rebellious Ur-Council of Nova Terra dismissed the authority of the High Lords of Terra and claimed separate rule over the Imperium's Segmentum Pacificus.
This was a period of division and civil war known as the Nova Terra Interregnum in which the Imperium was shattered into warring and disparate factions which cut across the lines of the Adeptas and turned former allies against each other.
During this period it was not just the Imperium which suffered from civil strife. The Adeptus Mechanicus was also afflicted with division and internal warfare brought about by doctrinal differences and competing powers.
One of the most acrimonious of these conflicts was the Moirae Schism, a dogmatic battle between Martian Cult Mechanicus orthodoxy and a radical creed based upon the prophetic writings of a triad of tech-mystics based on the minor Forge World of Moirae.
The Moirae Schism
The tech-creed of the Forge World of Moirae was based on the prophetic wave calculations of a triad of tech-mystics enshrined within Moirae's colossal data-looms who believed that they had discerned a series of predictive patterns within the micro-fluctuations of the Astronomican's beacon. They believed these so-called Gematric patterns contained the words of the Omnissiah from which the skein of future history and humanity's destiny could be read.
The Moirae Tech-priests compiled the fruits of their apocalyptic divinations within encrypted archives, copies of which quickly spread through many of the Cult Mechanicus' sects. These radical teachings included, among other visions and interpretations of the Emperor's will, veiled references to the future overthrow of Mars and the fusion of the Cult Mechanicus and the Ecclesiarchy into a unified state religion for the Imperium.
Such claims were treated (unsurprisingly) as dark sedition by the Mechanicus authorities on Mars and civil war was quickly sparked between the traditionalist and radical elements. One of the first casualties of the conflict was the Forge World of Moirae itself, which was reduced to a cinder by the Fabricator-General's rectification fleet.
But by this time the schismatic creed had spread across the galaxy. Conflict between the advocates of the Moirae doctrine, Martian orthodoxy and other opposing radical groups would continue to flare up intermittently throughout the next millennium before the schism was finally ended and its surviving adherents brought back into the Cult Mechanicus' fold.
The disruptive creed quickly gained influence, both within sects of the Mechanicus' priesthood as well as a number of Skitarii regiments and Titan Legions, causing untold harm before being transmitted even further afield to Space Marine Chapters with close ties to the Adeptus Mechanicus -- and in this the Iron Hands were no exception.
At that time, the majority of Whirlwinds Hyperios in service had been constructed according to the STC data held at the Forge World of Moirae. The rogue Tech-priests of Moirae utilised a hidden digital cipher insinuated into the machines during their construction to cause them to power down upon receiving the relevant code, which led many Space Marine Chapters to distrust the Hyperios to this day, refusing to deploy it in battle, despite its STC imprint being known to the vast majority of Adeptus Mechanicus Forge Worlds and Adeptus Astartes forges.
Of all the battles of the Moirae Schism, none were so expansive or long-lasting as the prolonged naval engagement over the nebula space fields of the Gulf of Black Shadows. There, mining wars between rival Forge Worlds escalated to massive fleet battles. It is estimated that the wrecks of over ten thousand starships -- from mining craft to vessels of war -- floated between the gas clouds.
Yet the battle was far from over, for within the floating graveyards, salvage crews continued the war for centuries, fighting each other in desperate boarding actions, each side seeking to reclaim valued technology. Entire robot maniples were recovered by opposing sides, and reprogrammed to attack their former controllers.
Another relevant campaign fought during the schism took place on the world of Ghosaris, where the Adeptus Custodes intervened and crushed an army of the Dark Mechanicum without mercy, deploying Venerable Contemptor Dreadnought Uriaxes. It is unclear what ties, if any, there were between the Moirae schismatics and the Dark Mechanicum.
Towards the end of the Schism in the 35th Millennium, a radical sub-sect of the Moirae creed known as the Xarisians indulged in rampant techno-heresy in the attempt to win the civil war that split the Adeptus Mechanicus.
Hunted down as Hereteks even by the members of their own creed, the dark adepts of the Xarisians were slaughtered and their malefic technologies destroyed. However, one of their creations -- the powerful Laser Destructor known as the Diamonas -- survived the war, and it is said that many bitter battles have been fought amongst the Fallen Houses of the Chaos Knights for its possession.
The Sons of Medusa
The Moirae doctrines were quickly embraced by a significant percentage of those within the Iron Hands Chapter, and championed by the infamous Omnissian mystic, Iron Father Setol Sollex among their clan companies.
Discord soon followed, and the Iron Hands rapidly approached the edge of an outright Chapter civil war. Clan Raukaan was notable during this time of conflict for holding staunchly to their Chapter's core beliefs. Under the influence of Iron Chaplain Furnous and Iron Captain Hekkan, they were one of the only clan companies to not have a single Battle-Brother become corrupted by the pernicious Moirae doctrine.
Indeed, they deployed several squadrons of Vindicators and Predators against rebellious Cataphractii forces during the Battle of Kamjada. That these Adeptus Mechanicus rebels were supported by a small cadre of warriors from the Iron Hands' Clan Borrgos would form a point of bitter contention between the two clan companies for many centuries to come.
Open civil war was only averted by the Iron Hands Great Clan Council's imposition of a settlement. Notoriously straightforward and harsh, their solution to avoid mass bloodshed within the ranks was a simple one -- exile for the minority who had embraced the dissident doctrine, and a binding treaty never to raise their hands against their former brothers enacted by both sides.
It is believed that fully a third of the Iron Hands brethren then departed, to be joined in time by a handful of other Space Marines from other Iron Hands Successor Chapters who shared their beliefs (although evidence exists that some like the Red Talons mercilessly destroyed their errant brothers over this matter, rather than suffer the dissidents to live).
This exiled faction still saw themselves as part of the Imperium and still members of the Iron Hands. Although reduced to a ragtag fleet, they swiftly set about locating and destroying enemy targets. Over time they slowly began to increase their numbers and strength, tithing their gene-seed to higher Imperial authorities and conducting their duty as if they were still part of their mother Chapter.
Over time, the exiled faction continued to use the iconography and pattern of the Iron Hands from which they had been outcast, with some minor variations. They further divided themselves into three new clan companies to support their steady increase in numbers, and eventually outlived the schism that had given them birth.
So matters continued until the dawning of the Age of Redemption. During this period the newly resurgent High Lords of Terra reassembled the disparate strands of anarchy and purged what could not be saved from the Imperium. The Moirae exiles of the Iron Hands, now a separate Chapter in all but name, were weighed and judged, their record examined in minute detail as was their gene-seed for unworthiness or deviance. They were found to be loyal and untainted.
As a result, by an almost unique edict, the newly renamed Sons of Medusa were reorganised and ratified as an official Chapter of the Adeptus Astartes within the Emperor's grace, despite protests by some within the Adeptus Mechanicus and the grave misgivings held by numerous other Space Marine Chapters.
Although the Sons of Medusa were born as a result of the Moirae Schism, it is unknown just how much of its teachings they still cleave to more than five millennia later. What is certain is that many factions of the Adeptus Mechanicus still view them with suspicion. Even their forebears, the Iron Hands, still treat them with cold civility at best.
In the late 39th Millennium, the Sons of Medusa established a series of fortified void stations on asteroids in the abandoned mining system of Taelus to serve as a more permanent facility for their fleet-based Chapter, constructing secure armouries, gene-seed banks and forges deep within the ferrous asteroid masses. The Taelus System is but a single solar day under Warp from what is now the Dead World of Moirae.
- Codex Adeptus Mechanicus - Skitarii (7th Edition), pg. 21
- Codex: Adeptus Mechanicus (8th Edition), "The Quest for Knowledge," pg. 34
- Codex: Adeptus Custodes (8th Edition), pg. 66
- Codex: Chaos Knights (8th Edition), pg. 68
- Codex: Space Marines (8th Edition) (Revised Codex), pg. 56
- Clan Raukaan - A Codex: Space Marines Supplement (6th Edition), pp. 19, 74
- Imperial Armour Volume Two - Second Edition: War Machines of the Adeptus Astartes, pg. 88
- Imperial Armour Volume Ten - The Badab War, Part Two, pp. 94, 96
- Warhammer 40,000: Rulebook (7th Edition), "The Ages of Mankind"