Basilica of St.Clement

San Clemente is Rome's most extraordinary layered church — three complete time periods stacked on top of one another, all accessible through a single building. Beneath the Romanesque basilica built around 1100 lies a 4th-century early Christian basilica, and beneath that a 1st-century complex including one of Rome's best-preserved Mithraic temples. Run by Irish Dominicans since 1677, it is essential for anyone who wants to understand how Rome built itself layer by layer across two millennia.