Vatican City travel guide

Vatican City, officially State of the Vatican City (Latin: Status Civitatis Vaticanae; Stato della Città del Vaticano), is a landlocked sovereign city-state whose territory consists of a walled enclave within the city of Rome. At approximately 44 hectares (108.7 acres), and with a population of around 900, it is the smallest state in the world by both population and area.
The state came into existence by virtue of the Lateran Treaty in 1929, which spoke of it as a new creation (Preamble and Article III), and not as a vestige of the much larger Papal States (756 to 1870) that had previously encompassed central Italy. Of which, most were absorbed into the Kingdom of Italy in 1860, and the city of Rome with a small area close to it, ten years later in 1870.
Vatican City is a non-hereditary, elected monarchy that is ruled by the Bishop of Rome — the Pope. The highest state functionaries are all clergymen of the Catholic Church. It is the sovereign territory of the Holy See (Sancta Sedes) and the location of the Apostolic Palace - the Pope's official residence - and of much of the Roman Curia.
For almost 1000 years (324-1309), the Popes lived at the Lateran Palace on the Caelian Hill in the east of Rome. On their return from 68 years in Avignon in 1377 the Lateran building was out of repair, and since then they have lived in the Vatican or, for a while, at the Quirinal, now the residence of the president of Italy. The Lateran Treaty by which the Vatican City State was set up is so called because it was signed in the restored Lateran building, which is now the residence of the Pope's Cardinal Vicar General for the City of Rome. There have been two Vatican Councils, but five Lateran Councils. The Basilica of St. John Lateran, not the St. Peter's Basilica in the Vatican, remains the Pope's cathedral. (...) more....