The Cog Mechanicum, also called the Opus Machina, is the ancient symbol used to represent both the Adeptus Mechanicus and their religious faith, the Cult Mechanicus, since before the signing of the Treaty of Mars in the 29th Millennium that incorporated the Priesthood of Mars into the newborn Imperium of Man. The emblem, a hybrid human/cyborg skull in front of a mechanical cog, represents the fusion of human flesh with machine that is the goal of every Mechanicus Adept. The members of the Mechanicus believe that slowly replacing portions of their organic bodies with more "pure" bionic replacements leads to a greater spiritual union with the Omnissiah, the Machine God who represents the sum total of all knowledge in the universe.
- Warhammer 40,000 Rulebook (5th Edition)
- Codex Imperialis (2nd Edition)
- Mechanicum (Novel) by Graham MacNeill