Internal factors

Several historical factors, which vary in importance depending on the time, help to account for the emergence of Roman Catholicism. The two factors that are often regarded as most decisive—at any rate by the champions of the primacy of Rome in the church—are the primacy of St. Peter among the Twelve Apostles of Christ and the identification of Peter with the church of Rome. Although there are considerable variations in the enumerations of the Apostles in the New Testament (Matthew 10:2–5; Mark 3:16–19; Luke 6:14–16; Acts 1:13) and further variations in the manuscripts, what they all have in common is that they list (in Matthew’s words) “first, Simon called Peter.” “But I have prayed,” Jesus said to Peter, “that your own faith may not fail; and once you have turned back, you must strengthen your brothers” (Luke 22:32) and “Feed my lambs.…Tend my sheep.…Feed my sheep” (John 21:15–17). In perhaps the most important passage, at least as it was later understood, Jesus said to Peter,

And so I say to you, you are Peter, and upon this rock [Greek petra] I will build my church, and the gates of the netherworld shall not prevail against it.
I will give you the keys to the kingdom of heaven. Whatever you bind on earth shall be bound in heaven; and whatever you loose on earth shall be loosed in heaven.

According to Roman Catholic teaching, this is the charter of the church—i.e., of the Roman Catholic Church.

The identification of this obvious primacy of Peter in the New Testament with the primacy of the church of Rome is not self-evident. For one thing, the New Testament is almost silent about a connection between Peter and Rome. The reference at the close of the Acts of the Apostles to the arrival of the Apostle Paul in Rome gives no indication that Peter was there as the leader of the Christian community or even as a resident, and the epistle that Paul had addressed somewhat earlier to the church at Rome devotes its entire closing chapter to greetings addressed to many believers in the city but fails to mention Peter’s name. On the other hand, in what is presumably a reference to a Christian congregation, the first of the two epistles ascribed to Peter uses the phrase “the chosen one at Babylon” (1 Peter 5:13), Babylon being a code name for Rome. It is, moreover, the unanimous testimony of early Christian tradition that Peter, having been at Jerusalem and then at Antioch, finally came to Rome, where he was crucified (with his head down, according to Christian tradition, in deference to the Crucifixion of Christ); there was and still is, however, disagreement about the exact location of his grave. Writing at about the end of the 2nd century, the North African theologian Tertullian (c. 160–c. 225) spoke of

Rome, from which there comes even into our own hands the very authority of the apostles themselves. How happy is its church, on which apostles poured forth all their doctrine along with their blood! where Peter endures a passion like his Lord’s! where Paul wins his crown in a death like that of John [the Baptist]!

Indeed, Rome could claim affiliation with two apostles, Peter and Paul, as well as numerous other martyrs for the faith.

In addition to this apostolic argument for Roman primacy—and often interwoven with it—was the argument that Rome should be honored because of its position as the capital of the Roman Empire: the church in the prime city ought to be prime among the churches. Rome drew tourists, pilgrims, and other visitors from throughout the empire and beyond and eventually became, for church no less than for state, what Jerusalem had originally been called, “the church from which every church took its start, the mother city [metropolis] of the citizens of the new covenant.” Curiously, after the newly converted emperor Constantine (died 337) transferred the capital of the Roman Empire from Rome to Constantinople in 330, Rome’s civil authority was weakened, but its spiritual authority was strengthened: the title “supreme priest” (pontifex maximus), which had been the prerogative of the emperor, now devolved upon the pope. The transfer of the capital also occasioned a dispute between Rome (“Old Rome”) and Constantinople (“New Rome”) over whether the new capital should be entitled to a commensurate ecclesiastical preeminence alongside the see (seat of a bishop’s office) of Peter. The second and fourth ecumenical councils of the church (at Constantinople in 381 and at Chalcedon in 451) both legislated such a position for the see of Constantinople, but Rome refused to acknowledge the legitimacy of that prerogative.

It was also at the Council of Chalcedon—which was convoked to resolve the doctrinal controversy between Antioch and Alexandria over the person of Jesus Christ—that the council fathers accepted the formula proposed by Pope Leo I (reigned 440–461), which offered the orthodox teaching of Christ’s Incarnation and of the union of both his natures. Recognizing the authority with which Leo spoke, the council fathers declared, “Peter has spoken through the mouth of Leo!” The council was only one in a long series of occasions when the authority of Rome, sometimes by invitation and sometimes by its own intervention, served as a court of appeal in jurisdictional and dogmatic disputes that had erupted in various parts of Christendom. During the first six centuries of the church, the bishop of every major Christian center was, at one time or another, charged with and convicted of heresy—except the bishop of Rome (though his turn would come). The titles that the see of Rome gradually assumed and the claims of primacy that it made within the life and governance of the church were, in many ways, little more than the formalization of what had become widely accepted practice.

External factors

In addition to various internal developments, at least two external factors contributed decisively at the beginning of the Middle Ages to the development of Roman Catholicism as a distinct form of Christianity. One was the rise of Islam in the 7th century. During the decade following the death of the Prophet Muhammad in 632, his followers captured three of the five “patriarchates” of the early church—Alexandria, Antioch, and Jerusalem—leaving only Rome and Constantinople, located at opposite ends of the Mediterranean and, eventually, also at opposite ends of the Schism of 1054.

The other external force that encouraged the emergence of Roman Catholicism as a distinct entity was the collapse of governmental and administrative structures in the Western Roman Empire in 476 and the migration into Europe of Germanic and other tribes that eventually established themselves as ruling elites. (The Eastern Roman Empire, with its capital at Constantinople, survived as the Byzantine Empire until 1453.) Some of these peoples, particularly the Goths, had already become Christian before their arrival in western Europe. The form of Christianity they had adopted in the 4th century, generally known as Arianism, was, according to the ecumenical Council of Nicaea, heretical in its doctrine of the Trinity. Therefore, the future of medieval Europe belonged not to the tribes that had converted to an unorthodox Christianity but to the tribes, particularly the Franks, that had adhered to traditional Germanic religion and later became Christian. The Franks, after their arrival in Gaul, accepted Catholic teaching on the doctrine of the Trinity as well as the authority of the Catholic bishops of Gaul. The coronation by the pope of the Frankish king Charlemagne (c. 742–814) as emperor of the Romans on Christmas Day 800 was the culmination of the long-standing alliance of the Franks and the church.

The early medieval papacy

During the centuries that marked the transition from the early to the medieval church, Roman Catholicism benefited from the leadership of several outstanding popes. Two of these popes—who are called “Saint” by the Roman Catholic Church and who are the only two popes called “the Great” by historians—merit special consideration, even in a brief article. Pope Leo I was, even for his pagan contemporaries, the embodiment of the ideal of “Romanness” in his resistance to the barbarian conquerors. In 452, with the help of the Apostles Peter and Paul and a host of angels (according to papal tradition), he persuaded Attila and the Huns to withdraw to the banks of the Danube, thus saving Rome from destruction. He repeated this triumph in 455, when his intercession with the Vandals mitigated their depredations in the city. His aforementioned intervention in the doctrinal controversy among Eastern theologians over the person of Christ and the role played by his Tome of 449 in the formula of the Council of Chalcedon in 451 were part of a concerted campaign by Leo to consolidate and extend the jurisdiction of the see of Rome to remote areas such as Gaul, Spain, and North Africa. This extended jurisdiction was officially acknowledged by the Roman emperor.

Pope Gregory I (reigned 590–604), more than any pope before or after him, laid the foundations for the Roman Catholicism of the Middle Ages. He sent St. Augustine of Canterbury (died 604/605) to bring about the conversion of England to the Christian faith, and he corresponded with the rulers of the Merovingian Franks and with the bishops of Gothic Spain. He built up papal administration in central Italy and negotiated with the Lombard rulers who occupied the peninsula. Rejecting the universalist claims of the patriarch of Constantinople, Gregory asserted papal primacy over moral issues and emphasized the humility of his office by styling himself the “servant of the servants of God.” His commitment to a life of service is demonstrated in his Pastoral Rule, a guidebook for bishops that outlines their obligations to teach and to serve as moral exemplars to their flocks. Gregory the Great was also one of the most important patrons of the Benedictine monastic movement, to which he owed a considerable part of his spiritual upbringing; he wrote a life of St. Benedict of Nursia (c. 480–c. 547).

Notwithstanding the contributions of these popes, medieval Roman Catholicism would not have taken the form it did without the conversion of the emperor Constantine in 312. Constantine legalized Christianity, promoted its interests, and took an active role in its institutional and doctrinal development. Even though some supported a heretical version of Christianity, all subsequent emperors except Julian the Apostate favored the faith. Theodosius I (347–395), however, made Catholic Christianity the official religion of the empire in 381 and prohibited the worship of pagan gods in 392. After Constantine every branch of Christendom had to work with rulers who claimed to profess its faith, and the manner in which the two main branches of the church (in Rome and Constantinople; before the Reformation) dealt with the state had a considerable impact on their development. As the church approached the conclusion of the first millennium of its history, it had become the legatee of the spiritual, administrative, and intellectual resources of the early centuries.

Most of the preceding analysis pertains to the whole of Christendom. The Eastern Orthodox Church has almost as large a share in the developments of the early centuries of Christianity as does the Roman Catholic Church, and even Protestantism looks to these centuries for its authentication. However, the Middle Ages may be defined as the era in which the distinctively Roman Catholic forms and institutions of the church were established. The following chronological account of medieval developments shows how these forms and institutions emerged from the context of the shared history of the early Christian centuries.