Cult of Mithras

Mithraism, also known as the Mithraic mysteries, was a Roman mystery religion centered on the god Mithras. The religion was inspired by Iranian worship of the Zoroastrian god Mithra, though the Greek Mithras was linked to a new and distinctive imagery, and the level of continuity between Persian and Greco-Roman practice is debated. The mysteries were popular among the Roman military from about the 1st to the 4th century CE.
Worshippers of Mithras had a complex system of seven grades of initiation and communal ritual meals. Initiates called themselves syndexioi, those "united by the handshake". They met in underground temples, now called mithraea (singular mithraeum), which survive in large numbers. The cult appears to have had its centre in Rome and was popular throughout the western half of the empire, as far south as Roman Africa and Numidia, as far north as Roman Britain, and to a lesser extent in Roman Syria in the east