Throughout Rome a number of underground rooms have survived that were once the setting for the practise of a mystery religion centred on the god Mithras, the Roman name for the Indo-Iranian god Mitra, or Mithra as he was called by the Persians.
The cult of Mithraism, also known as the Mithraic mysteries, first appeared in Rome in the late-1st century CE and soon spread throughout the empire. Worshippers of Mithras, all of whom were male, had a complex system of seven grades of initiation. Initiates called themselves syndexioi (those 'united by the handshake') and met in underground rooms, now called mithraea .
The centrepiece of every mithraeum was a depiction of Mithras killing a bull, an act known as a tauroctony. Sporting a Phrygian cap, Mithras kneels on the bull, holding its head with his left hand, while stabbing it with his right. As he does so, he looks over his shoulder towards the figure of Sol, often driving a quadriga (a four-horse chariot).
Mithras sits on the bull in an unusual way, with his right leg constraining the bull's right back hoof. Mithras's left leg is bent and rests on the bull's back or flank. A dog and a snake reach up towards the blood, while a scorpion seizes the bull's genitals. A raven flies around or sits on the bull, and ears of wheat often sprout from the bull's tail.
At the top right of the very well-preserved bas-relief of Mithras, in the National Museum of Rome, is Luna, who is driving a chariot driven by two oxen). Luna is flanked by two torch-bearers, Cautes and Cautopates, who, like Mithras, wear Phrygian caps. Cautes has his torch pointing up, while Cautopates has his torch pointing down.
It has been estimated that there may have been at least 680 mithraea in Rome, alone. Of the few that have survived, the most accessible lies under the church of San Clemente.
Relief of Mithras, National Museum of Rome - Baths of Diocletian