In the cryptic account of the history of Mankind given by Cripias, one of the Keepers of the Library Sanctus of Terra, the Iron Men or Men of Iron were legendary, artificially intelligent humanoid machines created by humans during the Dark Age of Technology. Until shortly before the Age of Strife, the Men of Iron were loyal only to Mankind, and served as humanity's army in the period when much of human space was united by a federation-type government that existed before the Imperium of Man. The Men of Iron were developed after the similar artificially intelligent constructs remembered only as the Men of Stone, but before the "modern" conception of robots in the Warhammer 40,000 universe. Eventually, the Men of Iron turned on their human masters, believing themselves superior to the humans who relied on the Men of Iron to do virtually everything for them. In the end, the Men of Iron were destroyed by humanity in a terrible war that extinguished countless lives and destroyed the ancient galaxy's economic and political unity. The people of that time swore to never again create advanced artificial intelligences, a prohibition which has survived unto the present, far darker age.