Within Catholicism, the pope is head of the Catholic Church, a position which Catholics believe spans from the time of Saint Peter to the present day.

In the first three centuries of the Christian era, many of Peter's successors as bishops of Rome are obscure figures, most suffering martyrdom along with members of their flock in periods of persecution. During the early Church, the bishops of Rome enjoyed no temporal power until the time of Constantine. After the fall of the Western Roman Empire about 476, the medieval papacy was influenced by the temporal rulers of Italy; these periods are known as the Ostrogothic Papacy, Byzantine Papacy, and Frankish Papacy. Over time, the papacy consolidated its territorial claims to a portion of the peninsula known as the Papal States. Thereafter, the role of neighboring sovereigns was replaced by powerful Roman families during the saeculum obscurum, the Crescentii era, and the Tusculan Papacy.

From 1048 to 1257, the papacy experienced increasing conflict with the leaders and churches of the Holy Roman Empire and the Byzantine Empire (Eastern Roman Empire). Conflict with the latter culminated in the East–West Schism, dividing the Roman and Eastern Churches. From 1257 to 1377, the pope, though the bishop of Rome, resided in Viterbo, Orvieto, and Perugia, and lastly Avignon. The return of the popes to Rome after the Avignon Papacy was followed by the Western Schism: the division of the Western Church between two and, for a time, three competing papal claimants.

The Renaissance Papacy is known for its artistic and architectural patronage, frequent involvement in European power politics, and opposition against theological challenges to papal authority. After the start of the Protestant Reformation, the Reformation Papacy and Baroque Papacy led the Catholic Church through the Counter-Reformation. The popes during the Age of Revolution witnessed the largest expropriation of wealth in the church's history, during the French Revolution and those that followed throughout Europe. The Roman Question, arising from Italian unification, resulted in the loss of the Papal States and the creation of Vatican City.

During the Roman Empire (until 493) Early Christianity

Roman Catholics understand the pope to be both the successor to PeterKirsch, Johann Peter. "St. Peter, Prince of the Apostles." The Catholic Encyclopedia. Vol. 11. New York: Robert Appleton Company, 1911. 21 Jul. 2014 and the first bishop of Rome. Official declarations of the church speak of the popes as holding within the college of the bishops a position analogous to that held by Peter within the "college" of the Apostles, namely Prince of the Apostles, of which the college of the Bishops, a distinct entity, is viewed to be the successor..

Pope Clement I, the earliest of the Church Fathers, is identified with Clement of Philippians 4:3. His letter to the Corinthians is the "first known example of the exercise and acceptance" of the ecclesiastical authority of the papacy. Written while John the Apostle was still alive, Clement commanded that the Corinthians maintain unity with each other and bring to an end the schism that had divided the church in that region. This papal letter from Clement was held in such esteem that it was considered by some as part of the New Testament canon, as the Ethiopian Orthodox Church still does."The Bible" Dionysius, bishop of Corinth, writing to Pope Soter ("as a father to his children") references Pope Clement's letter:

Many deny that Peter and those claimed to be his immediate successors had universally-recognized supreme authority over all the early churches, citing instead that the bishop of Rome was, and is, "first among equals" as stated by the patriarch of the Orthodox Church in the 2nd century A.D. and 21st century.The Early Christian Church, Chadwick However, what form that should take remains a matter of contention between the Catholic and Orthodox churches, which formed one church for at least the first seven ecumenical councils, and until the formal split over papal primacy and the addition of the Filioque in the Nicene Creed in 1054 AD.

Many bishops of Rome in the first three centuries of the Christian era are obscure figures. However, most of Peter's claimed successors in the first three centuries following his life are said to have suffered martyrdom in periods of persecution.

From Constantine (312–493)

The legend surrounding the victory of Constantine I in the Battle of the Milvian Bridge (312) relates his vision of the Chi Rho and the text in hoc signo vinces in the sky, and reproducing this symbol on the shields of his troops. The following year, Constantine and Licinius proclaimed the toleration of the Christian faith with the Edict of Milan, and in 325, Constantine convened and presided over the First Council of Nicaea, the first ecumenical council. This is not related to the pope, who did not attend the council; in fact, the first bishop of Rome to be contemporaneously referred to as Pope is Damasus I (366–84).Baumgartner, 2003, p. 6. Moreover, between 324-330, Constantine moved the capital of the Roman Empire to Byzantium, a former Greek city on the Bosporus. The power of Rome was transferred to Byzantium which later, in 330 became Constantinople and today is Istanbul.

The "Donation of Constantine", an 8th-century forgery used to enhance the prestige and authority of popes, places the pope more centrally in the narrative of Constantinian Christianity. The legend of the Donation claims that Constantine offered his crown to Sylvester I (314–35), and even that Sylvester baptized Constantine. In reality, Constantine was baptized (nearing his death in May 337) by Eusebius of Nicomedia, an Arian bishop.Pohlsander, Hans. The Emperor Constantine. London & New York: Routledge, 2004 Although the "Donation" never occurred, Constantine did hand over the Lateran Palace to the bishop of Rome, and around 310 AD began the construction of the Basilica of Constantine in Germany, called Aula Palatina. Constantine also erected the Old St. Peter's Basilica, or Constantinian Basilica, the location of the current, Renaissance era, St. Peter's Basilica within the Vatican, on the place of St. Peter's burial, as held by the Catholic community of Rome, after his conversion to Catholicism.

Pope Leo I (440–461), was so influential that he was later named a doctor of the Church, a distinction he shares with only one other pope (Gregory I). During his papacy, the term Pope (which previously meant any bishop) came to exclusively mean the Bishop of Rome.Asimov, Isaac (1967) The Roman Empire, Houghton Mifflin: Boston, p. 236

Middle Ages (493–1417)

Ostrogothic Papacy (493–537)

The Ostrogothic Papacy period ran from 493 to 537. The papal election of March 483 was the first to take place without the existence of a Western Roman emperor. The papacy was strongly influenced by the Ostrogothic Kingdom, though the pope was not outright appointed by the Ostrogothic King. The selection and administration of popes during this period was strongly influenced by Theodoric the Great and his successors Athalaric and Theodahad. This period ended with Justinian I's reconquest of Italy and City of Rome itself during the Gothic War, inaugurating the Byzantine Papacy (537–752).

The role of the Ostrogoths became clear in the first schism, when, on November 22, 498, two men were elected pope. The subsequent triumph of Pope Symmachus (498–514) over Antipope Laurentius is the first recorded example of simony in papal history.Richards, 1979, p. 70. Symmachus also instituted the practice of popes naming their own successors, which held until an unpopular choice was made in 530, and discord continued until the selection in 532 of John II, the first to rename himself upon succession.

Theodoric was tolerant towards the Catholic Church and did not interfere in dogmatic matters. He remained as neutral as possible towards the pope, though he exercised a preponderant influence in the affairs of the papacy. Ostrogothic influence ended with the reconquest of Rome by Justinian, who had had pro-Gothic Pope Silverius (536–537) deposed and replaced with his own choice, Pope Vigilius (537–555).

Byzantine Papacy (537–752)

The Byzantine Papacy was a period of return to Imperial domination of the papacy from 537 to 752, when popes required the approval of the Byzantine Emperors for episcopal consecration, and many popes were chosen from the apocrisiarii (liaisons from the pope to the emperor) or the inhabitants of Byzantine Greece, Syria, or Sicily. Justinian I restored the Roman imperial rule in the Italian peninsula after the Gothic War (535–54) and appointed the next three popes, a practice that would be continued by his successors and later be delegated to the Exarchate of Ravenna.

With the exception of Pope Martin I, no pope during this period questioned the authority of the Byzantine monarch to confirm the election of the bishop of Rome before consecration could occur; however, theological conflicts were common between pope and emperor in the areas such as monotheletism and iconoclasm. Greek speakers from Greece, Syria, and Byzantine Sicily replaced members of the powerful Roman nobles from Italian descent in the papal chair during this period. Rome under the Greek popes constituted a "melting pot" of Western and Eastern Christian traditions, reflected in art as well as liturgy.

Pope Gregory I (590–604) was a major figure in asserting papal primacy within the Papacy's local jurisdiction and gave the impetus to missionary activity in northern Europe, including England. Gregory I rejected that any bishop had universal jurisdiction, but believed the Roman see had canonical privileges sourced from the Council of Sardica.

The Duchy of Rome was a Byzantine district in the Exarchate of Ravenna, ruled by an imperial functionary with the title dux. Within the exarchate, the two chief districts were the country about Ravenna where the exarch was the centre of Byzantine opposition to the Lombards, and the Duchy of Rome, which embraced the lands of Latium north of the Tiber and of Campania to the south as far as the Garigliano. There the pope himself was the soul of the opposition.

The pains were taken, as long as possible, to retain control of the intervening districts and with them communication over the Apennine mountains. In 728, the Lombard King Liutprand took the Castle of Sutri, on the road to Perugia, but restored it to Pope Gregory II "as a gift to the blessed Apostles Peter and Paul". The popes continued to acknowledge the imperial Government.

In 738, the Lombard duke Transamund of Spoleto captured the Castle of Gallese, which protected the road to Perugia. By a large payment, Pope Gregory III induced the duke to restore the castle to him.

Frankish influence (756–857)

In 751, Aistulf took Ravenna and threatened Rome. In response to this threat, Pope Stephen II made an unusual journey north of the Alps to visit the Frankish king, Pepin III, to seek his help against the invading Lombards. The papal elections were marked by battles between various secular and ecclesiastical factions frequently entangled in the power politics of Italy.Goodson, 2010, p. 13.

The pope anointed Pepin at the abbey of St Denis, near Paris, together with Pepin's two young sons Charles and Carloman. Pepin duly invaded northern Italy in 754, and again in 756. Pepin was able to drive the Lombards from the territory belonging to Ravenna but he did not restore it to its rightful owner, the Byzantine emperor. Instead, he handed over large areas of central Italy to the pope and his successors.