Catholic Church

• 1. Introduction

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  The Catholic Church counts somewhere between 1.28 and 1.41 billion baptized members worldwide as of 2026, making it the largest Christian church on earth. Yet behind that single name sits something stranger than a single institution. It is in fact 24 autonomous churches: the Latin Church and 23 Eastern Catholic Churches, spread across nearly 3,500 dioceses and eparchies. The majority of its members now live in the Global South, in Africa, Asia, and Latin America. How did one church come to span so many traditions, so many languages, and so many centuries? Why does a man in Rome claim a line of succession running back to a fisherman named Peter? And how did a faith once persecuted in the Roman Empire end up shaping the universities, hospitals, and art of an entire civilization? The answers run through emperors, schisms, councils, and a small city-state enclaved inside a single Italian city.

• 2. A Word For Universal

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  Around AD 100, Ignatius of Antioch wrote a letter to the Smyrnaeans that contains the first known use of the phrase "the catholic church." His line reads: "Wheresoever the bishop shall appear, there let the people be, even as where Jesus may be, there is the universal katholike Church." The word "catholic" comes from the Greek katholikos, first attested as an adjective for the church in the early second century. Around 350, Cyril of Jerusalem used the name "Catholic Church" in his Catechetical Lectures to separate it from other groups that also called themselves the church. The label gained official force in 380, when Theodosius I, the last emperor to rule both halves of the Roman Empire, issued the edict De fide catolica and established the state church. Since the East-West Schism of 1054, the Eastern Orthodox Church has taken "Orthodox" as its own epithet, though its official name remains the "Orthodox Catholic Church." The term "Roman Catholic Church" entered English only after the Protestant Reformation of the late 16th century, when those who left communion became known as Protestants.

• 3. The Rock And The Successor

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  In the Gospel of Matthew, at the Confession of Peter, Christ names Peter as the "rock" upon which his Church will be built. From that scene the Catholic Church draws its claim that the bishop of Rome, the pope, is the successor of Saint Peter. The history is more tangled than the doctrine. Many scholars hold that Rome was governed by multiple presbyters and bishops until the mid-2nd century, when a single-bishop structure was adopted. Bart D. Ehrman argues Peter "could not have been the first bishop of Rome," noting the church "did not have anyone as its bishop until about a hundred years after Peter's death." Raymond E. Brown calls it anachronistic to speak of Peter as a local bishop of Rome, yet says Christians of that era saw him exercising roles that "contributed enormously" to seeing the bishop of Rome as the successor of Peter for the church universal. The church teaches that its public ministry began at Pentecost, fifty days after Christ is believed to have risen, when the apostles received the Holy Spirit for their mission.

• 4. Empire And Schism

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  In 313, Constantine the Great, the first Roman emperor to convert to Christianity, issued the Edict of Milan and legalized a faith whose followers had been persecuted for refusing to honor the pagan gods. He moved the imperial capital to Constantinople in 330. From around 350, the bishops of Rome steadily expanded their authority by intervening to help orthodox leaders during theological disputes. Justinian I, Byzantine emperor from 527 to 565, formalized the pentarchy of five great sees: Rome, Constantinople, Alexandria, Antioch, and Jerusalem. He also established a caesaropapism that let him regulate "the minutest details of worship and discipline," opening the Byzantine Papacy period from 537 to 752, when popes needed imperial approval for consecration. The breaks came in stages. The Church of the East split after the Council of Ephesus in 431, the Oriental Orthodox after the Council of Chalcedon in 451, and the great separation from the Eastern Orthodox was solidified by the Fourth Crusade and the sacking of Constantinople by renegade crusaders.

• 5. Monks, Universities, And Art

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  Benedict of Nursia, who lived from about 480 to 543, was one of the founders of Western monasticism, and his Rule shaped European culture by preserving and transmitting ancient culture through the Benedictine tradition. Monastic Ireland became a center of scholarship, and early Irish missionaries such as Columbanus and Columba carried Christianity across continental Europe and built monasteries there. Cathedral and monastic schools traced back to the 6th century, and several of them became universities beginning in the 11th century, including the University of Oxford, the University of Paris, and the University of Bologna. The Stanford historian Paul Legutko said the church sits "at the center of the development of the values, ideas, science, laws, and institutions" of Western civilization. The church was the primary sponsor of Romanesque, Gothic, Renaissance, Mannerist, and Baroque styles, backing artists such as Raphael, Michelangelo, Leonardo da Vinci, Sandro Botticelli, Fra Angelico, Tintoretto, Titian, Gian Lorenzo Bernini, and Caravaggio. In the early 13th century, the Dominican priest Thomas Aquinas wrote his Summa Theologica, fusing the legacy of Plato and Aristotle with Christian revelation.

• 6. Reform And Counter-Reform

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  In 1517, Martin Luther, an Augustinian friar in Germany, sent his Ninety-five Theses to several bishops, protesting doctrines and practices including the supposed sale of indulgences. His escalating works ended with On the Babylonian Captivity of the Church in 1520, which accused the pope of being the anti-Christ, and led to his excommunication in 1521. In Switzerland, Huldrych Zwingli and John Calvin pressed further criticisms, and the resulting Reformation gave birth to most Protestant denominations. Henry VIII of England petitioned Pope Clement VII for a declaration of nullity for his marriage to Catherine of Aragon, and when refused, passed the Acts of Supremacy to make himself Supreme Head of the Church of England. The Council of Trent, sitting from 1545 to 1563, became the engine of the Counter-Reformation, reaffirming teachings such as transubstantiation and the necessity of good works for salvation. Earlier, in 1415, the Bohemian preacher Jan Hus had been burned at the stake for refusing to recant Wycliffite heresies, his reform efforts foreshadowing Luther.

• 7. From Avignon To Chicago

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  In 1798, Napoleon's general Louis-Alexandre Berthier invaded the Italian Peninsula and imprisoned Pope Pius VI, who died in captivity, before Napoleon re-established the church in France through the Concordat of 1801. The papacy's troubles with secular power stretched back further. In 1309, Pope Clement V became the first of seven popes to live in Avignon, and after that papacy ended in 1376, a 38-year Western Schism began, with rival claimants in Rome, Avignon, and Pisa, resolved at the Council of Constance which named Martin V pope. The Italian unification of the 1860s absorbed the Papal States, including Rome itself from 1870, ending the papacy's temporal power, until the Lateran Treaty of 1929 recognized papal sovereignty over Vatican City. Modern popes reshaped the role. Pope John XXIII convened the Second Vatican Council, which from 1962 to 1965 introduced the most significant changes since Trent, allowing the Mass in the vernacular. John Paul II, elected in 1978 as the first non-Italian pope in 455 years, visited 129 countries. Pope Leo XIV, elected on the 8th of May 2025, is the first Augustinian pope and the first born in Chicago.

• 8. Sacraments And The Eucharist

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  Among the church's seven sacraments, the Eucharist is called "the source and summit of the Christian life," celebrated in the Mass. Catholics believe that through consecration by a priest, the bread and wine become the body and blood of Christ, a change called transubstantiation, where the substance changes while the visible accidents remain. The seven sacraments are baptism, confirmation, the Eucharist, penance, anointing of the sick, holy orders, and holy matrimony, and the Catechism groups them into Christian initiation, healing, and service of communion. Baptism washes away both original sin and personal sins, can be conferred even by non-Catholics using the Trinitarian formula, and marks a person permanently so it cannot be repeated. In the sacrament of penance, the priest is bound under the severest penalties to keep the "seal of confession," absolute secrecy about anything revealed to him. The Virgin Mary is venerated as the Mother of God, honored through the dogmas of the Immaculate Conception, defined by Pope Pius IX in 1854, and the Assumption, defined by Pope Pius XII in 1950. Today the church operates tens of thousands of institutions and is the largest non-government provider of education and health care in the world.