Basilica of San Clemente

It is indeed one of the most impressive archaeological sites in Rome, a three-layer historical wonder. In 1857 Friar Joseph started excavating under the 12th century church, and to his surprise found another church underneath, and also a Mithras temple underneath that one. Today visitors have the chance to see all three. The 12th century church is at street level and was built in 1108 by Pope Pachsal II and is unchanged from that time, beautifully decorated with frescoes and mosaics. Most of the second church was destroyed in 1084 by Norman invaders, but you can still catch a glimpse of some of the 11th century frescoes that were added. The lowest level is the darkest and least preserved, but you can still see its altar, where a god is slaying a bull, and get a sense of how old this temple must be. History even says that before this was a temple, it was actually an apartment building and mansion that was owned by Titua Flavius Clemens.