The Rome IndexBasilica of San Clemente
Three layers of Rome in one building — medieval church, 4th-century basilica, and a Mithraic temple below.
What it is
A working 12th-century basilica built over a 4th-century church, which was itself built over a 1st-century Roman building containing a Mithraic temple — one of the clearest illustrations of how Rome's layers sit directly on top of each other.
Going underground
A ticket covers the descent through the lower levels, where you can hear — and sometimes see — an underground stream that still runs through the lowest Mithraic level.
The mosaics
The 12th-century apse mosaic in the upper basilica is one of the finest in Rome, depicting the Triumph of the Cross with remarkable detail and color.