I. If Paul appealed to Peter how much more must ordinary folk have recourse to his successor.
To Leo, bishop of Rome.
If Paul, the herald of the Truth, the trumpet of the Holy Ghost, had recourse to the great Peter, in order to obtain a decision from him for those at Antioch who were disputing about living by the Law, much more do we small and humble folk run to the Apostolic See to get healing from you for the sores of the churches. For it is fitting that you should in all things have the pre-eminence, seeing that your See possesses many peculiar privileges. For other cities get a name for size or beauty or population, and some that are devoid of these advantages are compensated by certain spiritual gifts: but your city has the fullest abundance of good things from the Giver of all good. For she is of all cities the greatest and most famous, the mistress of the world and teeming with population. And besides this she has created an empire which is still predominant and has imposed her own name upon her subjects. But her chief decoration is her Faith, to which the Divine Apostle is a sure witness when he exclaims “your faith is proclaimed in all the world;” and if immediately after receiving the seeds of the saving Gospel she bore such a weight of wondrous fruit, what words are sufficient to express the piety which is now found in her? She has, too, the tombs of our common fathers and teachers of the Truth, Peter and Paul, to illumine the souls of the faithful. And this blessed and divine pair arose indeed in the East, and shed its rays in all directions, but voluntarily underwent the sunset of life in the West, from whence now it illumines the whole world. These have rendered your See so glorious: this is the chief of all your goods. And their See is still blest by the light of their God's presence, seeing that therein He has placed your Holiness to shed abroad the rays of the one true Faith.
Source: Letters (New Advent)