Leo, the name of thirteen among the popes of the Roman Catholic Church, of whom the following call for particular notice.—LEO I., surnamed 'the Great,' who is held a saint of the Roman Catholic Church, and is one of the most eminent of the Latin Fathers, was born of a distinguished family at Rome about the end of the 4th century. On the death of Sixtus III. in 440 Leo was chosen as his successor. It is in his pontificate that the regular series of papal letters and decretals may be said to commence. Leo's letters, addressed to all parts of the church, exhibit prodigious activity and zeal, and are used by Roman controversialists as an evidence of the extent of the jurisdiction of the Roman see. In a council held at Rome in 449 he set aside the proceedings of the Council of Ephesus, which had pronounced in favour of Eutyches (q.v.), summoned a new council at Chalcedon, in which his legates presided, and in which Leo's celebrated 'Dogmatical Letter' was accepted 'as the voice of Peter.' He interposed with Attila (q.v.) in defence of the Roman city and people, and subsequently with Genserich (q.v.). Leo died at Rome in 461. His works, the most important of which are his Letters and Sermons, were first printed in 1479, and afterwards by Quesnel (2 vols. Paris, 1675); but much better editions are those of Cacciari (1753-55) and Ballerini (1757). See books by Arendt (1835), Perthel (1843), Saint-Cheron (1846), Gore (1880), and Feltoe (Lib. Fathers, xii., 1896).
The pontificate of LEO III. is chiefly noticeable as the epoch of the formal establishment of the Empire of the West. He was a native of Rome, and succeeded Hadrian I. in 795. During the greater part of the 8th century the popes, through the practical withdrawal of the Eastern emperors, had exercised a temporal supremacy in Rome, which was fully recognised by the gift of Pepin, and placed under the protectorate of the Frank sovereigns, who received the title of Patrician. The pontificate of Leo, however, was a troubled one, and in 799 he was treated with much violence, and obliged to flee to Spoleto, whence he afterwards repaired to Paderborn, in order to hold a conference with Charlemagne. On his return to Rome he was received with much honour by the Romans, and the chiefs of the conspiracy against him were sentenced to banishment. In the following year (800) Charlemagne, having come to Rome, was solemnly crowned and saluted emperor by the pope, and the temporal sovereignty of the pope over the Roman city and state was formally established, under the suzerainty, however, of the emperor. In 804 Leo visited Charlemagne at his court at Aix-la-Chapelle. With Charlemagne's successor, Louis le Débonnaire, Leo was embroiled in a dispute about the right of sovereign jurisdiction in Rome, which had not been brought to a conclusion when Leo died in 816.