LEO I, Saint (surnamed THE GREAT), Pope from 440-461: b. Rome or Tuscany; d. Rome, 10 Nov. 461. Of the Roman popes only Leo I and Gregory I received the designation "Great." The earliest definite information con cerning Leo reveals him in 429 a deacon of the Roman Church under Pope Celestine I, and al ready a man of considerable repute for learn ing and sagacity. His connection with Gaul is shown by the fact that Cassianus wrote (De Incarnatione Domini contra Nestorium) (430 or 431) at the suggestion of Leo and dedicated the work to him. In 440 Leo was temporarily in Gaul, sent there by Emperor Valentinian III to adjust the dispute between the general Aetius and the chief magistrate Albinus, when Pope Sixtus III died, 19 August. While still absent Leo was elected Pope and upon his re turn was consecrated, 29 Sept. 440. He set about securing unity in the Church and in 443 began measures for the suppression of the Manichieans and other heretics, succeeding in returning many to the Church and in banishing others. He greatly strengthened the central authority of the Church and a signed evidence of his success exists in the edict of the Emperor Justinian III which directed that the authority of the bishop of Rome was necessary for any innovations, and that "the decree of the apostolic see should thenceforth be law." Leo's correspondence with Turibius of Astorga in 447 culminated in the denouncement of Prescil lianism by the Church in Spain; in 449 he held a council in Rome against the Eutyches, whose council held earlier in the year Leo denounced as the "Robber Synod" ; and in 451 he addressed to the General Council at Chalcedon, over which he presided by legates, his famous 'dog matic letter" to Flavian, defining the doctrine of the Incarnation. His letters are of great
importance in Church history and 143 of them are in existence, together with 30 written to him. When Attila threatened to invade Italy, after the fall of Aquileia, Valentinian sent Leo him were banished. In 800 Charles returned to Rome and was crowned by the Pope peror of the Romans. While the subordinate position of Leo became thus clearly defined the result was to ensure the protection of the em peror for the Roman Church and Christendom against the heathen, and the arrangement con tinued satisfactorily during Charles' lifetime. Upon the accession of Louis conspiracies were again formed against him, but Leo was warned in time and the conspirators were seized and punished. However, the question of sovereign jurisdiction in Rome was again revived and Leo died before a decision was reached. He was known as a benefactor of the poor and a patron of art. Among the mosaics made under his direction is one in the Lateran, Rome, showing Saint Peter giving the pallium to Leo III and the standard to Charles.