History › Classical age › Roman Empire
Christianity
from c. AD 30; Rome's state religion from 380· Idea, religion or movement· Middle East & Africa
Well documentedSolid records, physical evidence or scientific consensus.
A religion centered on Jesus as Messiah and Son of God, which grew from a small Jewish movement into the world's largest faith.
See it on the History map →What happened
After Jesus' death, apostles such as Peter preached in Jerusalem. Paul, a convert, took the message to non-Jews across the Roman world; his letters form much of the New Testament. Churches grew in cities despite periodic persecution. Constantine legalized Christianity in 313 and Theodosius made it the state religion in 380. Councils such as Nicaea (325) defined core beliefs like the Trinity. It later divided into Orthodox and Catholic (1054) and Protestant (from 1517) branches.
Why it matters
It shaped Western law, art, calendars, universities, charity and politics, and today has about 2.4 billion followers worldwide, including roughly a quarter of South Koreans.
How we know
Paul's letters, the Gospels, early Christian writers, Roman officials' reports such as Pliny's letter (c. 112), catacombs and church ruins, and council records.
Still debated
Why it grew so fast, from a few thousand followers to perhaps 5–6 million by AD 300, is debated; estimates and explanations vary.
Inside this (3)
Connections (8)
▸Roman Empire persecuted, then adopted ChristianityWell documented
The connection
For nearly three centuries Rome treated Christians as suspect for refusing to honor the emperor and the gods. Persecutions were local and occasional, then empire-wide under Decius (250) and Diocletian (303–311). Constantine legalized Christianity in 313, and in 380 Theodosius made it the state religion. Roman roads, cities and common languages helped it spread.
When and how
Across the empire, from Nero's persecution in Rome (AD 64) to Theodosius' Edict of Thessalonica (380).
How we know
Roman writers Tacitus and Pliny, imperial edicts, Christian martyr accounts and church histories.
Debates and open questions
How many Christians were killed is uncertain, with estimates in the thousands; early Christian writers may have exaggerated the scale.
▸Jesus of Nazareth is the central figure of ChristianityWell documented
The connection
Jesus' followers believed he rose from the dead and was the promised Messiah, in Greek 'Christos'. They gathered, shared meals, baptized converts and spread his teachings. At first a movement within Judaism, it opened to non-Jews within decades. Its scriptures, worship and beliefs all center on Jesus' life, death and resurrection.
When and how
Jerusalem and Galilee, c. AD 30–60; the apostles Peter and James, and Paul.
How we know
Paul's letters, written within about 25 years of Jesus' death, show communities already worshipping him across the eastern Mediterranean.
Debates and open questions
How far Jesus meant to found a new movement, rather than renew Judaism, is debated among historians and theologians.
▸Constantine the Great legalized and championed ChristianityWell documented
The connection
After his Milvian Bridge victory in 312, Constantine credited the Christian God. The Edict of Milan (313) ended persecution and returned confiscated church property. He gave churches money, land and legal privileges, built Old St. Peter's in Rome and the Church of the Holy Sepulchre in Jerusalem, and summoned the Council of Nicaea (325) to settle disputes over Christ's nature.
When and how
Rome, Milan and Nicaea (modern İznik, Turkey), 312–337; Constantine and some 250–300 bishops at Nicaea.
How we know
Eusebius' Life of Constantine, the edict's text preserved by Lactantius, his laws, and council records.
Debates and open questions
Whether his support came from genuine faith or politics, and how much imperial backing changed Christianity itself, are debated.
▸Kingdom of Aksum adopted ChristianityWell documented
The connection
Around 330 King Ezana was converted by Frumentius, a Syrian Christian captured as a youth and raised at the Aksumite court. Ezana's coins switched from pagan crescent symbols to the cross, among the first coins anywhere to carry it. Frumentius became Aksum's first bishop, appointed from Alexandria, tying Ethiopia's church to Egypt's for about 1,600 years.
When and how
Aksum, northern Ethiopia, c. 330–350; King Ezana and Frumentius, consecrated by Bishop Athanasius of Alexandria.
How we know
Ezana's coins and inscriptions, and the Roman church historian Rufinus' account of Frumentius.
Debates and open questions
How fast Christianity spread beyond the royal court is unclear; the 'Nine Saints', missionaries of the late 400s, may have done more.
▸The Crusades were waged in the name of ChristianityWell documented
The connection
Popes framed the crusades as armed pilgrimages: fighters took vows, sewed crosses on their clothing, and were promised forgiveness of sins (an indulgence). The idea was later aimed at other targets: Muslims in Spain, pagans in the Baltic, heretics in southern France, and even the pope's Christian enemies.
When and how
Launched at Clermont, France, in 1095 by Pope Urban II; later crusades were called by popes such as Eugene III, Gregory VIII and Innocent III.
How we know
Papal bulls and sermons; crusaders' vows; charters in which knights sold or pledged land to pay for the journey.
Debates and open questions
Historians debate how much ordinary crusaders were driven by faith versus land, loot or family duty; many lost money going.
▸Protestant Reformation split the Western branch of ChristianityWell documented
The connection
In 1517 Martin Luther attacked the sale of indulgences, payments to reduce punishment for sins, arguing that salvation comes by faith alone and authority from scripture, not the pope. Printing spread his protest fast. Lutheran, Calvinist, Anglican and other Protestant churches broke from Rome, while the Catholic Church reformed itself in response.
When and how
Wittenberg, Germany, 1517, then Switzerland, England, Scandinavia and beyond; Luther, Zwingli, Calvin and Henry VIII.
How we know
Luther's Ninety-five Theses and printed pamphlets, church records, and treaties such as the Peace of Augsburg (1555).
Debates and open questions
How much the Reformation was driven by faith, versus princes' politics, money and the printing press, is debated.
▸Tokugawa shogunate banned ChristianityWell documented
The connection
Jesuit missionaries, arriving from 1549, won perhaps 300,000 Japanese converts. The Tokugawa shoguns feared Christianity as a foothold for Spanish and Portuguese power and a rival loyalty. They banned it in 1614, expelled missionaries and executed believers, and after the Shimabara uprising (1637–38) shut out most Europeans. 'Hidden Christians' kept the faith secretly for over two centuries.
When and how
Japan, 1614–1873; shoguns Tokugawa Ieyasu, Hidetada and Iemitsu. The ban was lifted in 1873.
How we know
Shogunate edicts, Jesuit letters, and records of the Shimabara rebellion and the persecutions.
Debates and open questions
How much the ban was about religion, versus fear of foreign colonization and control of trade, is debated.
▸Darwin's On the Origin of Species challenged traditional readings of ChristianityMostly agreed
The connection
Darwin argued that species, by implication including humans, evolved by natural selection over vast time rather than being separately created. This challenged literal readings of Genesis and the argument that nature's design proves a designer. Reactions varied: some clergy welcomed evolution, others rejected it, and the Catholic Church and most mainline Protestant churches eventually accepted it.
When and how
England, from 1859; the 1860 Oxford debate between Bishop Samuel Wilberforce and Thomas Huxley; the 1925 Scopes trial in Tennessee.
How sure are we?
Published reviews, sermons and debates from the 1860s on, and later church statements such as Pope John Paul II's in 1996.
Debates and open questions
Historians debate whether science and religion were really at 'war', a framing popularized in the 1870s, or had a more complex relationship.