In Roman Catholicism, the doctrine that the pope, acting as supreme teacher and under certain conditions, as when he speaks ex cathedra (“from the chair”), cannot err when he teaches in matters of faith or morals. It is based on the belief that the church, entrusted with the teaching mission of Jesus, will be guided by the Holy Spirit in remaining faithful to that teaching. The First Vatican Council (1869–70) stated the conditions under which a pope may be said to have spoken infallibly: he must intend to demand irrevocable assent from the entire church in some aspect of faith or morals. The doctrine remains a major obstacle to ecumenical endeavours and is the subject of controversy even among Roman Catholic theologians.
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Territories of central Italy over which the pope had sovereignty from 756 to 1870. The extent of the territory and the degree of papal control varied over the centuries. As early as the 4th century, the popes had acquired considerable property around Rome (called the Patrimony of St. Peter). From the 5th century, with the breakdown of Roman imperial authority in the West, the popes' influence in central Italy increased as the people of the area relied on them for protection against the barbarian invasions. When the Lombards threatened to take over the whole peninsula in the 750s, Pope Stephen II (or III) appealed for aid to the Frankish ruler Pippin III (the Short). On intervening, Pippin “restored” the lands of central Italy to the Roman see, ignoring the claim of the Byzantine (Eastern Roman) Empire to sovereignty there. This Donation of Pippin (754) provided the basis for the papal claim to temporal power. More land was gained when the papacy acquired the duchy of Benevento in 1077, and Popes Innocent III and Julius II further expanded the papal domain. The rise of communes and rule by local families weakened papal authority in the towns, and by the 16th century the papal territory was one of a number of petty Italian states. They were an obstacle to Italian unity until 1870, when Rome was taken by Italian forces and became the capital of Italy. In 1929 the Lateran Treaty settled the pope's relation to the Italian state and set up an independent city-state (see Vatican City).
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