This innocuous-looking 11th-century church harbours some fascinating Roman excavations. Beneath the main church you can poke around the claustrophobic foundations of three Republican-era temples and the remnants of an Etruscan vegetable market. The temples, which were used as a prison in medieval times – hence carcere (prison) in the church's name – were incorporated into the church's structure as witnessed by the marble columns in the basilica's side.

Visits are by guided tour only and led by experts from the Sotterranei di Roma association.