Keys of Hel

"What are the Keys of Hel? They are the fires taken from the mountain. They are what should not and must not be. Only in the last days of humanity, when law has no meaning, should any think to break the locks placed upon them. These are those days."

- Iron Father Crius, Lord of Clan Kadoran, formerly of the Crusader Host, during the Horus Heresy

The Keys of Hel were the seals placed upon forbidden technologies from the Dark Age of Technology or of xenos origins by Ferrus Manus, Primarch of the Iron Hands Space Marine Legion during the Great Crusade era. This included the true rites of cybernetic resurrection. Where such elements of them were encountered (and indeed recognised for what they were only by the Iron Hands), they were seized and suppressed by the Primarch's express order and withheld, it was rumoured, even from the Mechanicum. Few outside the X Legion were even aware of the existence of such forbidden technology or nightmare sciences. Even the majority of those within the Iron Hands knew more than the names of such forbidden lore or technological devices. After the death of Ferrus Manus at the hands of his Chaos-corrupted Brother Primarch Fulgrim of the Emperor's Children during the Dropsite Massacre on Isstvan V, some of the Iron Hands who survived the slaughter and were mad with grief, resorted to the use of these forbidden technologies and 'turned the Keys of Hel', seeking out any advantage they could utilise against the Traitor Legions and exact their righteous vengeance for the loss of their gene-father.

History
"The true danger of the unknown lies not in its existence, but in knowing that it exists."

- Iterator Kyril Sindermann, in his speech to the Symposium of Nessus, Great Crusade, ca. M30

During the latter years of the Great Crusade the Iron Hand's obsession with strength and the elimination of physical and mental weakness led them to revere the machine and distrust the failings inherent in flesh. While other Space Marine Legions were bound in metal and laboured to create great machines of war, for the Iron Hands, inculcated in their own idiosyncratic beliefs inherited from the Cult Mechanicus' influence on Medusa, the machine was not merely an appendage to flesh but its inheritor. To them their Emperor-augmented transhuman bodies were neither more nor less than a living machine of blood and gristle made for war, a machine which could be repaired and improved upon as opportunity allowed and need commanded.

To be as strong as iron was the fire that drove the Iron Hands, and to speed recovery times cybernetic replacements, swifter by far to employ than the genetic regeneration and vat-grown transplant techniques commonly used by the Legiones Astartes, were favoured, and were capable of getting a fallen or severely injured Legionary back into the fight with frightening speed. As a result, no Iron Hands Legionary who had served in battle for any length of time was wholly without bionic augmentation, and such implants were marks of honour, and often improved and augmented away from the battle's pressing need. Some of the most veteran among the Iron Hands went so far that they were little more than machines cradling shreds of their former humanity. So it was with them that to be interred within a Dreadnought body and therefore be allowed to fight for their Primarch and the great cause of unifying humanity forever, was the highest honour any member of the X Legion could aspire to.

But there were limits to what even Ferrus Manus would countenance and, while he lived, certain mysteries of cybermancy such as the true rites of cybernetic resurrection remained proscribed as nightmare sciences of the Dark Age of Technology. Where such elements of them were encountered by the Iron Hands Legion during the Great Crusade (and indeed alone among the Legions they could easily recognise them for what they were), they were seized and suppressed by the Primarch's express order and withheld, it was rumoured, even from the Mechanicum. Whispers remained of such horrors as the Agesine Protocols, the Eight Sleepers, and the damned Sarcosan Formulae; all remained locked under the covenants of the so-called Keys of Hel, named for the mythic goddess of the Medusan pantheon. Kept deep within the vaults of Medusa and sunk in chambers on airless rocks orbiting lifeless star systems where none save a select few of the Iron Fathers of the X Legion knew of their location, they were put beyond reach but not destroyed. After the death of Ferrus Manus, however, some saw his resistance to a wider supplanting of flesh with steel as one of the flaws that had allowed him to be destroyed by the Traitors; that the impetuous rage that led him to his death was born of flesh and that flesh had failed him. Thereafter, in the dark times that followed, some among the Iron Hands saw virtue in what had once been forbidden and, it is said, turned the Keys of Hel -- and opened the path to heretekal damnation.