Mithraism an ancient religion. It was one of several pagan religions popular in the Roman Empire before Christianity became the prevailing faith in the fourth century A.D. Mithraism was one of the ancient mystery cults, its rites and doctrines being known only to initiates. Mithraism left no written records, and knowledge of the religion comes mainly from painted and sculpted images found in underground temples.

The most important image in each temple is a young man (presumably Mithras) slaying a bull with a dagger. Some scholars relate the image to an ancient Persian myth (Mithras, or Mithra, was the Persian god of light) and some to an astrological myth involving the constellations Perseus and Taurus.

Mithraism arose in Asia Minor in the first century B.C. It was widely followed by soldiers, public officials, and merchants. Women were excluded. Mithraism was a strong rival of Christianity during the second and third centuries, but after the conversion of Emperor Constantine the Great to Christianity in the early fourth century, Mithraism was suppressed and soon disappeared.