The church of San Clemente is probably the most interesting in Rome, with layer upon layer of religious history and works of art from almost each of the last twenty centuries.

The story begins in the crumbling alley in the picture, part of the ancient Roman city that burned while Nero famously fiddled. The somewhat less spooky next level is a temple to Mithras built by Roman soldiers on top of the charred remains of the old city around the year 200 AD. The adherents sat in the chairs lining the wall, and shared communal suppers on the white altar in the middle, while behind this room is another where boys were taught the complicated details of the religion. When Christianity became the state religion, a Christian church was built on top of the Mithraic temple (the plain white windowless building in the photo). This church was then burned by the Normans as part of the general destruction of the neighborhood in 1084, whereupon the stunning presentday church was built on the rubble. The current church is decorated with some of the best mosaics in Rome, plus some relics of the earlier church.