The Mithraeum of Santa Prisca

Every mithraeum is the same room. It is small, it holds a few dozen people at most, it has no windows, and it is arranged as a long vaulted space with a raised bench down each side and the image of Mithras killing the bull at the far end. The vault is a cave, and where no natural cave was available one was constructed, which is what happened under the Aventine.

Manfred Clauss notes that the consistency of the plan across the empire, from the Rhine forts to Rome to Syria, is one of the strongest pieces of evidence that this was a single organised cult and not a loose family of local practices. The benches tell you what the room was for. Members reclined along them and ate, facing each other across a narrow floor, with the bull slaying scene in view at the end. The size caps the congregation, and that is a structural fact about the religion: a mithraeum could not become a mass movement in the shape it had, because when a group outgrew the room the answer was another room rather than a bigger one. Rome held a large number of them. The Santa Prisca sanctuary, excavated from 1953 beneath a church on the Aventine hill, is among the best preserved anywhere in the empire, and its particular interest is that its walls were painted and a large part of the paint survived the centuries of burial that followed.

Mithraism left no scripture. Nothing written by an initiate about the meaning of the cult survives, and what is known comes from images, inscriptions and the layout of the rooms, which is why a painted wall counts as a major source. At Santa Prisca a procession of figures runs along the side walls with inscriptions naming grades of initiation. That gives the sequence of seven grades, from Raven at the bottom through Bridegroom, Soldier, Lion, Persian and Runner of the Sun to Father, each associated with a planetary power. Without the Santa Prisca paintings and a small number of comparable finds such as the mosaic floor at Ostia, the grade system would be known only in outline.

What the grades meant is still argued. Roger Beck reads the mithraeum and its imagery as a deliberate model of the cosmos through which an initiate was understood to ascend, while other scholars are more cautious about how much doctrine can be recovered from images alone. The atlas records the grades as attested and their interpretation as debated. The cult admitted men only, was strong in the army and among imperial officials and freedmen, and disappeared within a few generations of the fourth century laws against public sacrifice, leaving its rooms to be filled in or built over.