Dedicated to Saint Clement, the third pope after Saint Peter.  There are 3 levels each belonging to a different era.  On the main level the columns are "recycled" from ancient Roman monuments.  The arches located by the door to the sacristy area/ ticket office for the archaeological site are from the underground basilica. No pictures or videos are allowed underground.                               

San Clemente, near the Coliseum, is a perfect example of how history still exists in layers in Rome’s churches. The current twelfth century church features probably the most beautiful mosaic in Rome, and sits on top of a fourth century church built over a first century Christian meeting place that’s above a first century BC Mithraic temple and school.                                       The remains of St Clement I (d. 80) and of St Ignatius of Antioch (d. 107) rest beneath the main altar.  A chapel on the right side of the nave is dedicated to Saints Cyril (d. 869) and Methodius (d. 885). The relic of St Cyril found in the 1960’s rests within the altar of this chapel.