The Mechanicus essentially maintains an empire-within-an-empire in Imperial space, and its interests usually, but not always, coincide with those of the wider Imperium. The Mechanicus acknowledge the Emperor of Mankind as the ruler of the Imperium of Man, but not the religious truth of the Imperial Cult or the Ecclesiarchy, and are granted an unusual amount of political and religious autonomy within the Imperium's structure, a role protected by the ancient Treaty of Mars. This occurred after the Red Planet had fallen to the control of the Hereteks who represented the Traitor faction of the Mechanicum loyal to the Warmaster Horus later called the ' Dark Mechanicum.' The Adeptus Mechanicus was formally separated from the larger Mechanicum of Mars by order of the Council of Terra in 012.M31. In ancient times, before the current Age of the Imperium officially began following the end of the Horus Heresy, the Adeptus Mechanicus was instead called the Mechanicum. The tech-adepts of the Mechanicus are the primary keepers of what is viewed as sacred wisdom, a privileged caste of Tech-priests who jealously guard the knowledge required to maintain and construct much of the Imperium's advanced technology.

The Adeptus Mechanicus is the official Imperial name within the Adeptus Terra for the Cult Mechanicus or Cult of the Machine based on Mars which provides the Imperium with its scientists, engineers and technicians.

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