Vatican City, the smallest state in the world, lies on the Vatican Hill across the Tiber from ancient Rome. In the first century the area held imperial gardens and the circus of Caligula and Nero, and tradition holds that the apostle Peter was martyred there and buried in the neighbouring cemetery, where Constantine later built the first basilica of St Peter.

The bishops of Rome, at first leaders of a persecuted community, became the chief authority in the city as the Western Empire collapsed. Under Byzantine rule they fed and defended Rome, and in 756 the Donation of Pepin made them sovereigns of the Papal States, a territory across central Italy that they ruled, with interruptions, for more than eleven centuries.

Popes crowned emperors, fought the Hohenstaufen, lived at Avignon and returned to rebuild Rome as princes of the Renaissance, raising the new St Peter's and the Sistine Chapel. Revolutionary France and Napoleon twice abolished their state, and the Italian Risorgimento ended it: on 20 September 1870 Italian troops took Rome, and the popes withdrew into the Vatican as self-declared prisoners.

This Roman Question was settled by the Lateran Treaty of 1929, which created the State of Vatican City, 44 hectares ruled by the pope as sovereign and administered through the Secretariat of State and the Governorate. Home to the Swiss Guard, the Vatican Museums and the central government of the Catholic Church, the city state has lasted through war and reform to the present. Explore the fifteen ages below through selected events from the timeline.