Papal state, independent since 1929, situated within the city of Rome. Here, on the site of the Ager Vaticanus, Emperor Caligula (a.d. 37–41) began a circus that was completed by Emperor Nero (54–68).
According to tradition, St. Peter was martyred near the Circus of Nero, c. 65, and an oratory was constructed on the site by Pope Anacletus II c. 155. In c.
325 Pope Sylvester I persuaded Emperor Constantine I to erect a basilica to St. Peter on the hill. Charlemagne was crowned emperor of the West in this basilica in 800. In the 15th century the old basilica began to be replaced, a section at a time, by the present church, St. Peter’s Basilica, which was completed in 1626 according to plans by Raphael, Bramante, Michelangelo, and others. In 1656 Bernini completed the famous piazza with the colonnade that now forms the gateway to Vatican City.
Behind St. Peter’s Basilica are the Sistine Chapel, with its famous frescoes by Perugino, Pinturicchio, Boticelli, and others, and the ceiling and Last Judgement by Michelangelo. In the papal palace are the stanze and loggia of Raphael and the Borgia apartments.
Also in the Vatican City are the Vatican Library, one of the most important in the world, with its collection of manuscripts and printed books, and the Vatican Museums with their collections of Egyptian, Etruscan, Greek, Roman, early Christian, Renaissance, and baroque arts.
The Vatican City proper does not include the area of the Vatican once part of the medieval Borgo, or Leonine City, which was surrounded by the Leonine wall built by Pope Leo IV in 850 against the Saracens; nor does it include the Castel Sant’Angelo, built as the Mausoleum of Hadrian in a.d. 135 and long a papal fortress. The Castel was most famously used during the sack of Rome under Emperor Charles V in 1527, and it was where Benvenuto Cellini and others were imprisoned. Until 1377, when the papacy returned to Rome from Avignon, the Lateran Palace in Rome was the official residence of the pope. The cathedral of St. John Lateran in Rome remains the official seat of the pope as bishop of Rome.
The Lateran Treaties (La Conciliazione), negotiated on February 11, 1929, between Pope Pius XI and Benito Mussolini gave the Vatican City full extraterritoriality within Italy. This extended not only to the Vatican Hill but also to other buildings in and around Rome, including the Lateran Cathedral and Palace, the basilica of Sta. Maria Maggiore of the fourth and fifth centuries, the basilica of San Paolo fuori le Mura, down the Tiber, first built in the fourth century and rebuilt in 1854, the Renaissance Cancelleria Palace, and others, including the papal villa at Castel Gand olfo. In 1984, a new concordat between the Vatican and Italy modified certain provisions of the earlier Lateran treaty, including the primacy of Roman Catholicism as the Italian state religion. The Swiss Guard, formed in 1506, is still the official peacekeeping force of Vatican City.