The mystery cult of Mithras became evident in Rome towards the end of the first century AD. During the next two centuries, carried by its soldier and merchant devotees, it spread tot he frontier of the western empire from Britain to Bosnia. Perhaps because of odd similarities between the cult and their own religion the early Christians energetically suppressed it, frequently constructing churches over the caves (Milthraea) in which its rituals took place. By the end of the fourth century the cult was extinct.
The Roman Cult of Mithras
Edinburgh University Press