In 1935 during excavations, undertaken by the Fathers Augustines, a Mithraeum was discovered in the underground rooms of a notable house, situated under and behind the absis of the Church of S. Prisca on the Aventine. This Church lies above the house, in which an early Christian community had its meeting-place next to the house, the underground rooms of which served for the mithraists to held their services.
The Mithraeum is on the east side of the crypt, beyond the foundations of the apse. It faces east, i.e. towards the point of the rising sun, where the altar is situated.