The official cathedral of Rome, it's actually San Giovanni in Laterano, not St. Peter's, that serves as the ecclesiastical seat of the bishop of Rome—also known as the pope. San Giovanni dates back to the 4th century, when Emperor Constantine obtained the land from the wealthy Laterani family and donated it to the Church. But thanks to vandals, earthquakes, and fires, today's building owes most of its form to 16th- and 17th-century restorations, including an interior designed by baroque genius Borromini. Before you go inside, look up: At the top of the towering facade, done for Pope Clement X in 1736, 15 colossal statues (the 12 apostles plus Christ, John the Baptist, and John the Evangelist) stand watch over the suburbs spreading from Porta San Giovanni.
Despite the church's baroque design, some earlier fragments do remain. Under the portico on the left stands an ancient statue of Constantine, while the central portal's ancient bronze doors were brought here from the Forum's
Curia. Inside, the fragment of a fresco on the first pillar is attributed to the 14th-century Florentine painter Giotto; it depicts Pope Boniface VIII proclaiming the first Holy Year in 1300. The altar's rich Gothic tabernacle—holding what the faithful believe are the heads of Sts. Peter and Paul—dates from 1367. Head to the last chapel at the end of the left aisle to check out the cloister. Encrusted with 12th-century Cosmatesque mosaics by father-and-son team the Vassallettos, it's a break from baroque...and from the big tour groups that tend to fill the church's interior. Around the corner, meanwhile, stands one of the oldest Christian structures in Rome. Emperor Constantine built the Baptistery in AD 315. While it's certainly changed over time, thanks to several restorations, a 17th-century interior redecoration, and even a Mafia-related car bombing in 1993, the Baptistery remains much like it would have been in ancient times.