The Basilica di San Clemente is a remarkable multi-layered archaeological site in Rome, consisting of a 12th-century basilica built over a 4th-century church, which itself sits atop a 1st-century Roman house. The current basilica, constructed just before the year 1100, boasts stunning gold mosaics in its apse, as well as intricate Cosmatesque marble flooring that reflects the craftsmanship of the 12th century. The choir area, or 'schola cantorum,' features beautiful carvings on marble panels, adding to the splendor of the upper basilica.

Beneath the basilica lies the first church, built in the 4th century. It contains some of the oldest frescoes in Rome, including depictions of the life of Saint Clement. These frescoes illustrate important moments in Christian history, and some even include early examples of the Italian vernacular language. Deeper still is a Mithraeum, an ancient temple devoted to Mithras, a Persian deity popular among Roman men during the 2nd and 3rd centuries. The temple includes a stone altar adorned with a relief of Mithras slaying a bull, surrounded by benches where worshippers would gather during ceremonies.

The Basilica di San Clemente has been under the care of the Irish Dominicans since the 17th century, who were responsible for initiating the excavations that revealed the site's many historical layers. The excavations have unearthed not only the Mithraeum but also the remains of earlier Roman structures, such as an industrial building that might have served as an imperial mint. Visitors can explore these archaeological wonders to gain insights into the diverse phases of Rome’s history.