As historians and theologians alike will tell us, it is not uncommon to find that a modern day church has been built upon the foundations of an earlier church or temple. But what is unusual is when these multiple layers are well preserved and easily identifiable. And even rarer is the chance for modern day tourists to view these layers first hand.

This is what is so special about the Basilica di San Clemente. There’s nothing of especially noteworthiness about the structure from the street. In fact, you could pass by the treasures contained within if you didn’t know to look for it. But once inside, you will have the opportunity to literally walk backwards in time.

The most modern part of the church is the façade, which was built in the 18th century. It houses a 12th century basilica that features an intricate mosaic of the Triumph of the Cross. Beneath this layer is a 4th century church, where frescoes depicting St. Clement and his miracles were added in the 11th century, and gave the church its name. This layer is actually still under excavation by the monks who live there. The lowest and most ancient layer dates to the 1st century B.C., which was a temple to the god Mithras.

The church is located near the Colosseum on the Via di S. Giovanni. Take the metro to the Colosseum stop, then head down Via S. Giovanni towards the Basilica of San Giovanni in Laterno.