Vatican City

The territory now occupied by Vatican City lies on the right bank of the Tiber, on a low rise historically known as the Mons Vaticanus. In Roman times the area was largely outside the city proper and contained gardens, a circus built under Caligula and completed by Nero, and burial grounds along the Via Cornelia. Christian tradition holds that the apostle Peter was martyred in Nero's circus and buried in the adjacent necropolis, a belief that drew pilgrims to the site from the late first century onward and shaped the religious geography of the area for the next two millennia.

In 326 the emperor Constantine ordered the construction of a great basilica over the supposed tomb of Peter, anchoring the rise of the Vatican as a Christian centre even as the secular capital of the empire shifted eastward to Constantinople. After the collapse of Roman authority in the west, the bishops of Rome accumulated extensive landholdings in central Italy. The Donation of Pepin in 756, in which the Frankish king Pepin the Short transferred conquered Lombard territories to Pope Stephen II, is conventionally taken as the founding moment of the Papal States, a temporal dominion ruled from Rome that endured, with interruptions, for more than a thousand years. The papal residence shifted between the Lateran, Avignon during the period 1309 to 1377, and finally the Vatican palaces, which became the principal seat from the late fifteenth century. Old St. Peter's was replaced by the present basilica between 1506 and 1626.

The Papal States were extinguished by the unification of Italy. French troops that had protected papal Rome withdrew during the Franco-Prussian War, and on 20 September 1870 forces of the Kingdom of Italy entered the city. Rome was annexed and made the Italian capital the following year. Pope Pius IX rejected the Italian Law of Guarantees and confined himself to the Vatican, beginning the period of the so-called Roman Question, during which successive popes regarded themselves as prisoners and refused to recognise Italian sovereignty over the former papal capital.

The dispute was settled on 11 February 1929, when Cardinal Secretary of State Pietro Gasparri and Prime Minister Benito Mussolini signed the Lateran Treaty. The agreement created the State of the Vatican City as a sovereign enclave of roughly 0.49 square kilometres, recognised the Holy See as a subject of international law, and provided financial compensation for the lost Papal States. During the Second World War the city remained formally neutral under Pius XII; after 1945 it developed as a small but globally connected centre of Catholic governance, expanded its diplomatic network, and became a permanent observer at the United Nations in 1964.

The latter twentieth and early twenty-first centuries were marked by the long pontificate of John Paul II from 1978 to 2005, the resignation of Benedict XVI in 2013, the election of Francis later that year, and his successor elected in 2025. Vatican City today is an absolute elective monarchy under the sovereignty of the reigning pope, who exercises legislative, executive, and judicial authority through the Roman Curia and a Pontifical Commission that administers the territory itself.