Legacy of the House of Haarlock.
The Tech-Priests of the Adeptus Mechanicus are the guardians of Earth’s ancient knowledge. The order owns and administrates the factory planet Mars, whose vast orbital workshops turn out the majority of the weapons, spacecraft, and other technologically sophisticated
machinery used in the Imperium. The Adeptus Mechanicus is as much an arcane cult as a scientific body, and its knowledge goes beyond mere technology into the realms of technoarcana.