Downstairs at San Clemente (same hours; L4000) there’s the nave of an earlier church , dated back to 392 AD, with a frescoed narthex depicting, among other things, the Miracle of San Clemente. And at the orient end of this church, steps lead down to a third level, the remains of a Roman house - a complex set of rooms including a wet Mithraic temple of the late second century, set among several rooms of a Roman house built after the fire of 64 AD. In the temple is preserved a statue of Mithras slaying the bull and the seats upon which the worshippers sat during their ceremonies. The underground river that formerly fed the lake in front of the Domus Aurea can be heard rushing to its destination in the Tiber, behind the Circo Massimo, a reminder that Rome is built on very shaky foundations indeed. Next door to the Roman house, crossways a narrow alleyway, are the ground-floor rooms of a first-century imperial building, all of which can be explored by the spooky light of fluorescent tubes set in the ceiling and along the mossy brick walls.