Leo I (440-461) and Gregory I (590-604) are the only two bishops of Rome commonly called "the Great." Leo, at a time when the capital of the Empire had been moved to Constantinople, and the government even in Italy no longer had its headquarters at Rome, was the most important official in the city. To him fell such prosaic tasks as supervising the distribution of grain imports and reorganizing the municipal fire department. When Attila and the Huns invaded Italy in 452, he negotiated their withdrawal, and when Gaiseric (or Genseric) the Vandal captured Rome three years later, it was Leo who prevented the total destruction of the city. It is perhaps not surprising that the theory of papal supremacy gained much ground in his day.
In his day there were disagreements about the correct way to state the truth that Jesus Christ is both God and man. In 449 Leo wrote a letter (known as the Tome of Leo) to Bishop Flavian of Constantinople, in which he affirmed that Christ has two natures in one person (hypostatic union). The letter was read in 451 by the Council of Chalcedon (the fourth Ecumenical Council), and judged by them to be sound doctrine. It contributed much to the creedal statements of that council.
Propers for Leo I of Rome - Bishop and Theologian
O Lord our God, grant that thy Church, following the teaching of thy servant Leo of Rome, may hold fast the great mystery of our redemption, and adore the one Christ, true God and true Man, neither divided from our human nature nor separate from thy divine Being; through the same Jesus Christ our Lord, who liveth and reigneth with thee and the Holy Ghost, one God, now and for ever. Amen.
The Epistle - 2 Timothy 1:6-14.
The Holy Gospel - St. Matthew 5:13-19.
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