A Persian Bull-Slayer in Rome, Maybe

A study of the Roman cult of Mithras, which appeared across the Roman Empire from the first century CE and became especially popular among soldiers, traces the god's name directly to the Zoroastrian and wider Iranian deity Mithra, and ancient Roman writers themselves sometimes described the mysteries as of Persian origin, transmitted west through territory the Parthian Empire controlled. On this reading, Parthian era Persia would have served as the transmission point through which an ancient Iranian god was carried into an entirely new Roman mystery religion.

That derivation has been argued against by more recent scholarship. A study of the origins of the Mithraic mysteries makes the case that the Roman cult, for all it borrowed the god's name and some Persian sounding imagery, was substantially a Roman invention, its astrological symbolism and initiatory structure owing more to Hellenistic astronomy than to any continuous Persian ritual tradition, with no clear evidence of a Parthian Mithraic mystery cult resembling the Roman one. The dispute remains open rather than settled, and it is a useful example of how thin the Parthian empire's own religious record is: much of what can be said about Parthian era Mithra worship is inferred backward from what the Romans made of the god's name, rather than read directly from Parthian sources.