This is the Cathedral of Rome, founded by Constantine during the IV century. Through the history it was destroyed and rebuilt many times. The present Cathedral dates back to the XII century. The facade was built by Alessandro Galilei, in 1735. On the top of the balustrade 15 statues stand, representing Jesus Christ and the Doctors of the Church. In the arcade on the left side you can admire the statue of Constantine, coming from the Imperial Thermae of the Quirinal. Just like Saint Peter's church, there is the Holy Door, open only in the jubilee years. The interior of the Cathedral is 130 mts. high, and to its building several important architects collaborated, among whom Borromini. The golden ceiling particularly strikes you; it was designed by Pirro Ligorio. The very big central nave, shows in its background the imposing tabernacle dating back to the second half of the XIV century, in which you can see some frescos attributed to Barna from Siena. The relics of the remains of San Pietro's and San Paolo's skulls are contained in precious silver containers. You can see under the tabernacle the papal altar wanted by Urbano V in 1367, on which only the Pope can celebrate the mass.