The archeological complex that lies under the Basilica of San Clemente is situated in the valley that separates the Caelius Mountain from the Esquiline Hill. The currently visible structures belong to two buildings. The former consists of a house of at least two storeys built between the end of the first and the beginning of the second century AD. 

Successively between the end of the second and the beginning of the third century the central room of the house was transformed into a Mithreum. The side walls of the central room of the sanctuary present two long benches, where the congregation sat. The altar for the cult was placed at the rear of a niche, where Mithra is depicted killing a bull with his two assistant torch-holders, Cautes and Cautopates. 

The Mithreum was abandoned at the end of the fourth century and the entire complex was filled in. The latter building is situated east of the Mithreum and at a lower level. The complex probably served as a storehouse or, based on inscriptions found in the zone, as a mint for the production of imperial coins. 

Around the middle of the third century the first floor of the building was demolished and replaced by a new construction to be identified with the Titulus of Clement quoted by the sources, seat of the first Christian community in the zone. In the course of the fourth century the building was partly demolished to build the early Christian church that is still visible underneath the current one.