Was the office of the pope a 4th-5th century invention? Here's what the Early Church Fathers say about the office of pope (aka Bishop of Rome)... yes, Rome... where Peter traveled and was then martyred.
"The blessed apostles [Peter and Paul], having founded and built up the church [of Rome] . . . handed over the office of the episcopate to Linus" (Against Heresies 3:3:3 [A.D. 189]).
"[T]his is the way in which the apostolic churches transmit their lists: like the church of the Smyrneans, which records that Polycarp was placed there by John, like the church of the Romans, where Clement was ordained by Peter" (Demurrer Against the Heretics 32:2 [A.D. 200]).
The Little Labyrinth
"Victor . . . was the thirteenth bishop of Rome from Peter" (The Little Labyrinth [A.D. 211], in Eusebius, Church History 5:28:3).
Cyprian of Carthage
"The Lord says to Peter: ‘I say to you,’ he says, ‘that you are Peter, and upon this rock I will build my Church, and the gates of hell will not overcome it. ... ’ [Matt. 16:18]. On him [Peter] he builds the Church, and to him he gives the command to feed the sheep [John 21:17], and although he assigns a like power to all the apostles, yet he founded a single chair [cathedra], and he established by his own authority a source and an intrinsic reason for that unity. . . . If someone [today] does not hold fast to this unity of Peter, can he imagine that he still holds the faith? If he [should] desert the chair of Peter upon whom the Church was built, can he still be confident that he is in the Church?" (The Unity of the Catholic Church 4; first edition [A.D. 251]).
"Cornelius was made bishop by the decision of God and of his Christ, by the testimony of almost all the clergy, by the applause of the people then present, by the college of venerable priests and good men, at a time when no one had been made [bishop] before him—when the place of [Pope] Fabian, which is the place of Peter, the dignity of the sacerdotal chair, was vacant. Since it has been occupied both at the will of God and with the ratified consent of all of us, whoever now wishes to become bishop must do so outside. For he cannot have ecclesiastical rank who does not hold to the unity of the Church" (Letters 55:):8 [A.D. 253]).
"With a false bishop appointed for themselves by heretics, they dare even to set sail and carry letters from schismatics and b.asphemers to the chair of Peter and to the principal church [at Rome], in which sacerdotal unity has its source" (ibid., 59:14).
Eusebius of Caesarea
"Paul testifies that Crescens was sent to Gaul [2 Tim. 4:10], but Linus, whom he mentions in the Second Epistle to Timothy [2 Tim. 4:21] as his companion at Rome, was Peter’s successor in the episcopate of the church there, as has already been shown. Clement also, who was appointed third bishop of the church at Rome, was, as Paul testifies, his co-laborer and fellow-soldier [Phil. 4:3]" (Church History 3:4:9–10 [A.D. 312]).
Pope Julius I
"[The] judgment [against Athanasius] ought to have been made, not as it was, but according to the ecclesiastical canon. . . . Are you ignorant that the custom has been to write first to us and then for a just decision to be passed from this place [Rome]? If, then, any such suspicion rested upon the bishop there [Athanasius of Alexandria], notice of it ought to have been written to the church here. But now, after having done as they pleased, they want to obtain our concurrence, although we never condemned him. Not thus are the constitutions of Paul, not thus the traditions of the Fathers. This is another form of procedure, and a novel practice. . . . What I write about this is for the common good. For what we have heard from the blessed apostle Peter, these things I signify to you" (Letter on Behalf of Athanasius [A.D. 341], contained in Athanasius, Apology Against the Arians 20–35).
Council of Sardica
"[I]f any bishop loses the judgment in some case [decided by his fellow bishops] and still believes that he has not a bad but a good case, in order that the case may be judged anew . . . let us honor the memory of the apostle Peter by having those who have given the judgment write to Julius, bishop of Rome, so that if it seem proper he may himself send arbiters and the judgment may be made again by the bishops of a neighboring province" (Canon 3 [A.D. 342]).
"You cannot deny that you are aware that in the city of Rome the episcopal chair was given first to Peter; the chair in which Peter sat, the same who was head—that is why he is also called Cephas [‘Rock’]—of all the apostles; the one chair in which unity is maintained by all" (The Schism of the Donatists 2:2 [A.D. 367]).
Epiphanius of Salamis
"At Rome the first apostles and bishops were Peter and Paul, then Linus, then Cletus, then Clement, the contemporary of Peter and Paul" (Medicine Chest Against All Heresies 27:6 [A.D. 375]).
Pope Damasus I
"Likewise it is decreed: . . . [W]e have considered that it ought to be announced that . . . the holy Roman Church has been placed at the forefront not by the conciliar decisions of other churches, but has received the primacy by the evangelic voice of our Lord and Savior, who says: ‘You are Peter, and upon this rock I will build my Church, and the gates of hell will not prevail against it; and I will give to you the keys of the kingdom of heaven, and whatever you shall have bound on earth will be bound in heaven, and whatever you shall have loosed on earth shall be loosed in heaven’ [Matt. 16:18–19]. The first see [today], therefore, is that of Peter the apostle, that of the Roman Church, which has neither stain nor blemish nor anything like it" (Decree of Damasus 3 [A.D. 382]).
"[Pope] Stephen . . . was the blessed Peter’s twenty-second successor in the See of Rome" (Against the Luciferians 23 [A.D. 383]).
"Clement, of whom the apostle Paul writing to the Philippians says ‘With Clement and others of my fellow-workers whose names are written in the book of life,’ the fourth bishop of Rome after Peter, if indeed the second was Linus and the third Anacletus, although most of the Latins think that Clement was second after the apostle" (Lives of Illustrious Men 15 [A.D. 396]).
"Since the East, shattered as it is by the long-standing feuds, subsisting between its peoples, is bit by bit tearing into shreds the seamless vest of the Lord . . . I think it my duty to consult the chair of Peter, and to turn to a church [Rome] whose faith has been praised by Paul [Rom. 1:8]. I appeal for spiritual food to the church whence I have received the garb of Christ. . . . Evil children have squandered their patrimony; you alone keep your heritage intact" (Letters 15:1 [A.D. 396]).
"I follow no leader but Christ and join in communion with none but your blessedness [Pope Damasus I], that is, with the chair of Peter. I know that this is the rock on which the Church has been built. Whoever eats the Lamb outside this house is profane. Anyone who is not in the ark of Noah will perish when the flood prevails" (ibid., 15:2).
"The church here is split into three parts, each eager to seize me for its own. . . . Meanwhile I keep crying, ‘He that is joined to the chair of Peter is accepted by me!’ . . . Therefore, I implore your blessedness [Pope Damasus I] . . . tell me by letter with whom it is that I should communicate in Syria" (ibid., 16:2).
Ambrose of Milan
"[T]hey [the Novatian heretics] have not the succession of Peter, who hold not the chair of Peter, which they rend by wicked schism; and this, too, they do, wickedly denying that sins can be forgiven [by the sacrament of confession] even in the Church, whereas it was said to Peter: ‘I will give unto thee the keys of the kingdom of heaven, and whatsoever thou shalt bind on earth shall be bound also in heaven, and whatsoever thou shall loose on earth shall be loosed also in heaven’[Matt. 16:19]" (Penance 1:7:33 [A.D. 388]).
"If all men throughout the world were such as you most vainly accuse them of having been, what has the chair of the Roman church done to you, in which Peter sat, and in which Anastasius sits today?" (Against the Letters of Petilani 2:118 [A.D. 402]).
"If the very order of episcopal succession is to be considered, how much more surely, truly, and safely do we number them from Peter himself, to whom, as to one representing the whole Church, the Lord said, ‘Upon this rock I will build my Church’ . . . [Matt. 16:18]. Peter was succeeded by Linus, Linus by Clement, Clement by Anacletus, Anacletus by Evaristus . . . " (Letters 53:1:2 [A.D. 412]).
Council of Ephesus
"Philip the presbyter and legate of the Apostolic See said: ‘There is no doubt, and in fact it has been known in all ages, that the holy and most blessed Peter, prince and head of the apostles, pillar of the faith, and foundation of the Catholic Church, received the keys of the kingdom from our Lord Jesus Christ, the Savior and Redeemer of the human race, and that to him was given the power of loosing and binding sins: who down even to today and forever both lives and judges in his successors. The holy and most blessed pope Celestine, according to due order, is his successor and holds his place, and us he sent to supply his place in this holy synod’" (Acts of the Council, session 3 [A.D. 431]).
Pope Leo I
"As for the resolution of the bishops which is contrary to the Nicene decree, in union with your faithful piety, I declare it to be invalid and annul it by the authority of the holy apostle Peter" (Letters 110 [A.D. 445]).
"Whereupon the blessed Peter, as inspired by God, and about to benefit all nations by his confession, said, ‘You are the Christ, the Son of the living God.’ Not undeservedly, therefore, was he pronounced blessed by the Lord, and derived from the original Rock that solidity which belonged both to his virtue and to his name [Peter]" (The Tome of Leo [A.D. 449]).
"We exhort you in every respect, honorable brother, to heed obediently what has been written by the most blessed pope of the city of Rome, for blessed Peter, who lives and presides in his own see, provides the truth of faith to those who seek it. For we, by reason of our pursuit of peace and faith, cannot try cases on the faith without the consent of the bishop of Rome" (Letters 25:2 [A.D. 449]).
Council of Chalcedon
"After the reading of the foregoing epistle [The Tome of Leo], the most reverend bishops cried out: ‘This is the faith of the fathers! This is the faith of the apostles! So we all believe! Thus the orthodox believe! Anathema to him who does not thus believe! Peter has spoken thus through Leo! . . . This is the true faith! Those of us who are orthodox thus believe! This is the faith of the Fathers!’" (Acts of the Council, session 2 [A.D. 451]).