LEO I., who alone of Roman pontiffs shares with Gregory I. the surname of THE GREAT, pope from 440 to 461, was a native of Rjme, or, according to a less probable account, of Volterra in Tuscany. In 429, when the first unmistakable reference to Pope Leo occurs, he was still only a deacon, but already a man of com manding influence ; it was at his suggestion that the De incarna tions of the aged Cassianus, having reference to the Nestorian heresy, was composed in that year, and about 431 Cyril of Alexan dria wrote to him to prevent the Roman Church from lending any support to the ambitious schemes of Juvenal of Jerusalem. In 440, while Leo was in Gaul, whither he had been sent to compose some differences between Aetius and another general named Al binus, Pope Sixtus III. died. The absent archdeacon was unani mously chosen to succeed him, and was consecrated on Sept. 29. In 443 he began to take stern measures against the Manichaeans (who since the capture of Carthage by Genseric in 439 had become very numerous at Rome), and in 444 he was able to report to the Italian bishops that some of the heretics had returned to Catholi cism, while many had been sentenced to perpetual banishment "in accordance with the constitutions of the Christian emperors," and others had fled ; in seeking these out the help of the provincial clergy was sought. During the earlier years of Leo's pontificate Hilarius of Arles was compelled to return to his obedience to the Roman See. The edict of Valentinian III. (445) denounced the contumacy of the Gallic bishop, and enacted "that nothing should be done in Gaul, contrary to ancient usage, without the authority of the bishop of Rome, and that the decree of the apostolic see should henceforth be law." In 448 he received with commendation a letter from Eutyches, the Constantinopolitan monk, complaining of the revival of the Nestorian heresy there; and in 449 Eutyches asked for Leo's sup port at the oecumenical council at that time under summons to meet at Ephesus. Leo then by his legates sent to Flavian the epistle setting forth in detail the doctrine ever since recognized as orthodox regarding the union of the two natures in the one person of Jesus Christ. Leo's letter, though submitted, was not read by the
assembled fathers at the Synod of Ephesus and the papal legates were in danger of their lives from the violence of the theologians who, not content with deposing Flavian and Eusebius, shouted for the dividing of those who divided Christ. When the news of the result of this council reached Rome, Leo wrote to Theodosius re questing the emperor to sanction another council, to be held this time, however, in Italy.
Among the reasons urged by Leo for holding this council in Italy had been the threatening attitude of the Huns ; their irrup tion took place in the following year (452). After Aquileia had succumbed to Attila's long siege, the conqueror set out for Rome. Near the confluence of the Mincio and the Po he was met by Leo, whose eloquence persuaded him to turn back. Legend has sought to enhance the impressiveness of the occurrence by an unneces sarily imagined miracle. The pope was less successful with Gen seric when the Vandal chief arrived under the walls of Rome in 455, but he secured a promise that there should be no incendiarism or murder, and that three of the oldest basilicas should be exempt from plunder—a promise which seems to have been faithfully ob served. Leo died on Nov. io, 461, the liturgical anniversary being April i 1. His successor was Hilarius or Hilarus, who had been one of the papal legates at the "robber" synod in 449 The title of doctor ecclesiae was given to Leo by Benedict XIV. Leo was a great preacher. From his short and pithy Sermones many of the lessons now to be found in the Roman breviary have been taken.