This interesting Mithraeum with a rich marble decoration was built in the IInd century in the basement of a large building adjacent to the Circus Maximus. It was formed by various rooms that preceded the actual sanctuary, the spelaeum or cave in which the contact with god took place through the various degrees of initiation. The sanctuary was destined to the mystery rites of the god Mithras , the Iranian -Babylonian deity whose worship found the maximum spread in the Roman Empire, especially between the IInd and IVth centuries AD. Central act of the myth was the killing of the cosmic bull who, dying, gives life to the universe. The representation of the myth was on a great carved relief found out of place and now situated in the center of the sanctuary. Above the relief is the inscription of the donor : “At the unconquered sun god Mithra, Hermes Tiberius Claudius “.