This church, not St. Peter’s, is officially the cathedral of the diocese of Rome; the Pope celebrates Mass here on certain holidays. Though it was built in A.D.. 314 by Constantine, only parts of the original baptistery remain; what you see today is an 18th-century facade by Alessandro Galilei (note signs of damage from a 1993 terrorist bomb) and an interior by Borromini, built for Pope Innocent X. In a misguided redecoration long ago, frescoes by Giotto were apparently destroyed; remains attributed to Giotto, discovered in 1952, are displayed against the first inner column on the right.
Across the street, the Santuario della Scala Santa (Palace of the Holy Steps), Piazza San Giovanni in Laterano 14 (tel. 06-7726641), is a set of 28 marble steps supposedly brought from Jerusalem by Constantine’s mother, Helen. Though some historians say the stairs might date only from the 4th century, legend claims these were the stairs Christ climbed at Pontius Pilate’s villa the day he was sentenced to death. Today pilgrims from all over the world come here to climb the steps on their knees.