The Adeptus Mechanicus is the ancient machine cult that safeguards the technological legacy of Mankind, a priesthood of augmented savants who worship the Machine God they name the Omnissiah. From their red world of Mars and the forge worlds scattered across the galaxy, they forge the weapons, ships, and engines upon which the Imperium's survival depends, and without their labour the whole edifice of human civilisation would grind to a halt within a generation.
To the tech-priests, knowledge is holy and technology sacred, each machine possessed of a machine-spirit that must be soothed with incense, litany, and ritual. They do not innovate so much as venerate, for the greatest secrets of humanity's golden age were lost long ago, and the Mechanicus now guards fragmentary Standard Template Construct designs like scripture, reproducing them without ever daring to alter the holy pattern. To seek new invention is often deemed the gravest heresy, an affront to the perfection of the ancients.
The cult is a power unto itself, bound to the Imperium by the ancient Treaty of Mars yet governed by its own hierarchy of magi, archmagos, and the supreme Fabricator-General. Its priesthood replaces frail flesh with blessed augmetics until little that is human remains, its adepts crossing the void in vast forge-fleets and marching to war behind the towering war-engines of the Titan Legions and the ranks of the Skitarii.
Proud, secretive, and jealous of its monopoly on knowledge, the Adeptus Mechanicus is both indispensable partner and eternal rival to Terra. Its beliefs, structure, and strange devotions are examined at length in the account of the Adeptus Mechanicus, the keepers of the flame in an age that has forgotten how it was first lit.