The Zoroastrian cult of Mithras, the god of light, had, in ancient Rome, considerable diffusion among the military; in the imperial period it competed with Christianity, with which it shows some similarities. Mithras was born of a virgin, on December 25, in a cave; dies at 33; the followers, in his memory, celebrate a meal at the same table.
A Roman itinerary of the Mithraic places includes the Basilica of San Clemente, the Mitreo Barberini and that of Santa Prisca.
Under the Basilica of San Clemente there are at least four underground levels dedicated to the Mithraic cult. The vault resembles that of a cave with the followers' seats on either side. In the middle is the altar with the representation of a sacrifice: the god Mitrhas kills a bull and a dog bites the animal, while a snake licks its blood and a scorpion grabs his testicles. The Italian superstitious gesture of the horns refers to the sacrificial bull.
The Mitreo Barberini, behind the homonymous palace, is among the best preserved in the city. The most interesting part is the painting on the back wall. In addition to the usual sacrifice, the zodiac signs are represented, a lion-headed god wrapped in the coils of a snake represents the flowing of time, the sun and the moon. On the sides of the central scene, ten small paintings of various sizes depict the story of the god Mithras.
The access to the Mitreo of Santa Prisca is on the right side of the church. The decorated hall presents a particularly original datum: the nudity of the god Mithras and a lying Saturn modeled from amphora pieces covered with stucco. The frescoes on the walls depict on the right the seven degrees of initiation to worship and on the left the procession in honor of Mithras and the Sun.