"If Paul, the herald of the truth, the trumpet of the Holy Spirit, hastened to the great Peter, to convey from him the solution to those in Antioch, who were at issue about living under the law, how much more do we, poor and humble, run to the Apostolic Throne (Rome) to receive from you (Pope Leo) healing for wounds of the Churches. For it pertains to you to have primacy in all things; for your throne is adorned with many prerogatives."
-Theodoret, Bishop of Cyrus in Syria (450) (Theodoret Ibid, Epistle Leoni)
"Neither to John, nor to any other of the disciples, did our Savior say, 'I will give to thee the keys of the Kingdom of Heaven,' but only to Peter."
-Eulogius of Alexandria (581) (Eulogius, Lib. ii. Cont. Novatian. ap. Photium, Biblioth, cod. 280)
"...For he only speaks in vain who thinks he ought to persuade or entrap persons like myself, and does not satisfy and implore the blessed Pope of the most holy Catholic Church of the Romans, that is, the Apostolic See, which is from the incarnate of the Son of God Himself, and also all the holy synods, according to the holy canons and definitions has received universal and supreme dominion, authority, and power of binding and loosing over all the holy churches of God throughout the whole world."
-Saint Maximus the Confessor (c. 650) (Maximus, Letter to Peter, in Mansi x, 692).
"Without whom (the Romans presiding in the seventh Council) a doctrine brought forward in the Church could not, even though confirmed by canonical decrees and by ecclesiastical usage, ever obtain full approval or currency. For it is they (the Popes of Rome) who have had assigned to them the rule in sacred things, and who have received into their hands the dignity of headship among the Apostles."
Saint Nicephorus, Patriarch of Constantinople (758-828) (Nicephorus, Niceph. Cpl. pro. s. imag. c 25 [Mai N. Bibl. pp. ii. 30]).
"Since to great Peter, Christ our Lord gave the office of Chief Shepherd after entrusting him with the keys of the Kingdom of Heaven, to Peter or his successor must of necessity every novelty in the Catholic Church be referred. [Therefore], save us, oh most divine Head of Heads, Chief Shepherd of the Church of Heaven."
-Saint Theodore the Studite of Constantinople (759-826), writing to Pope Leo III (Theodore, Bk. I. Ep. 23)
"Hear, O Apostolic Head, divinely-appointed Shepherd of Christ's sheep, keybearer of the Kingdom of Heaven, Rock of the Faith upon whom the Catholic Church is built. For Peter art thou, who adornest and governest the Chair of Peter..." -Saint Theodore the Studite of Constantinople (759-826), writing to Pope Paschal (Letter of St. Theodore and four other Abbots to Pope Paschal, Bk. ii Ep. 12, Patr. Graec. 99, 1152-3)
"Order that the declaration from old Rome be received, as was the custom by Tradition of our Fathers from of old and from the beginning. For this, O Emperor, is the highests of the Churches of God, in which first Peter held the Chair, to whom the Lord said: Thou art Peter ...and the gates of hell shall not prevail against it."
-Saint Theodore the Studite of Constantinople (759-826), writing to Emperor Michael (Theodore, Bk. II. Ep. 86)
"I witness now before God and men, they have torn themselves away from the Body of Christ, from the Supreme See (Rome), in which Christ placed the keys of the Faith, against which the gates of hell (I mean the mouth of heretics) have not prevailed, and never will until the Consummation, according to the promise of Him Who cannot lie. Let the blessed and Apostolic Paschal (Pope St. Paschal I) rejoice therefore, for he has fulfilled the work of Peter."
-Saint Theodore the Studite of Constantinople (759-826), (Theodore Bk. II. Ep. 63).
"In truth we have seen that a manifest successor of the prince of the Apostles presides over the Roman Church. We truly believe that Christ has not deserted the Church here (Constantinople), for assistance from you has been our one and only aid from of old and from the beginning by the providence of God in the critical times. You are, indeed the untroubled and pure fount of orthodoxy from the beginning, you the calm harbor of the whole Church, far removed from the waves of heresy, you the God-chosen city of refuge."
-Saint Theodore the Studite of Constantinople (759-826) (Letter of St. Theodore and Four Abbots to Pope Paschal).
"Let him (Patriarch Nicephorus of Constantinople) assemble a synod of those with whom he has been at variance, if it is impossible that representatives of the other Patriarchs should be present, a thing which might certainly be if the Emperor should wish the Western Patriarch (the Roman Pope) to be present, to whom is given authority over an ecumenical synod; but let him make peace and union by sending his synodical letters to the prelate of the First See."
-Saint Theodore the Studite of Constantinople (759-826) (Theodore the Studite, Patr. Graec. 99, 1420)