Christianity is the predominant religion in Europe. Christianity has been practiced in Europe since the first century, and a number of the Pauline Epistles were addressed to Christians living in Greece, as well as other parts of the Roman Empire.
According to a 2010 study by the Pew Research Center, 76.2% of the European population identified themselves as Christians. 
As of 2010, Roman Catholics were the largest Christian group in Europe, accounting for more than 48% of European Christians. The second-largest Christian group in Europe were the Orthodox, who made up 32% of European Christians. About 19% of European Christians were part of the mainline Protestant tradition. Russia is the largest Christian country in Europe by population, followed by Germany and Italy.
Since at least the legalization of Christianity by the Roman Emperor Constantine in the 4th century, Europe has been an important centre of Christian culture, even though the religion was inherited from the Middle East and important Christian communities have thrived outside Europe such as Oriental Orthodoxy and the Church of the East since the time of Christ. Christian culture has been an important force in Western civilization, influencing the course of philosophy, art, and science.
Historically, Europe has been the center and "cradle of Christian civilization". Christianity played a prominent role in the development of the European culture and identity. Europe has a rich Christian culture, especially as numerous saints and martyrs and almost all the popes were European themselves. All of the Roman Catholic popes from 741 to 2013 were from Europe. Europe brought together many of the Christian holy sites and heritage and religious centers.
History.
Early history.
Historians believe that St. Paul wrote his first epistle to the Christians of Thessaloniki (Thessalonians) around AD 52. His Epistle to the Galatians was perhaps written even earlier, between AD 48 and 50. Other epistles written by Paul were directed to Christians living in Greece (1 Corinthians, 2 Corinthians, Philemon, Philippians, 2 Thessalonians) and Rome (Romans) between the 50s and 70s of the first century.
The Record of Saint Dorotheus (Bishop of Tyre) is that the Church at Tyre sent Aristobulus (of the seventy) to Britain as bishop in AD 37. The Church seems to have been begun by him around the Bristol Channel area and 150 years later we have names of bishops recorded. By AD 550 there are recorded 120 bishops spread throughout the British Isles.
Before they were a recognized religion in Europe, Christians faced punishment and persecution for their first centuries in Europe, especially during the first. They were targeted by Emperor Nero who is rumored to have ordered the colossal fire in Rome, destroying the city in AD 64. The reasons for their persecution vary. Many believe Christians to have been scapegoats, when the real issues were local or political.
Armenia was the first state in the world to adopt Christianity as its state religion in AD 301. The oldest state-built church in the world, Etchmiadzin Cathedral, was built between AD 301–303. It is the seat of the Armenian Apostolic Church. The Roman Empire officially adopted Christianity in AD 380. During the Early Middle Ages, most of Europe underwent Christianization, a process essentially complete with the Baltic Christianization in the 15th century. The emergence of the notion of "Europe" or the "Western World" is intimately connected with the idea of "Christendom", especially since Christianity in the Middle East was marginalized by the rise of Islam from the 7th century, a constellation that led to the Crusades, which although unsuccessful militarily were an important step in the emergence of a religious identity of Europe. At all times, traditions of folk religion existed largely independent from official denominations or dogmatic theology.
From the Middle Ages onwards, as the centralized Roman power waned in southern and central Europe, the dominance of the Catholic Church was the only consistent force in Western Europe.
Movements in art and philosophy, such as the Humanist movement of the Renaissance and the Scholastic movement of the High Middle Ages, were motivated by a drive to connect Catholicism with Greek thought imported by Christian pilgrims.
East–West Schism and Protestant Reformation.
The East–West Schism of the 11th century and the Protestant Reformation of the 16th divided "Christendom" into hostile factions. Following the Age of Enlightenment of the 18th century, atheism and agnosticism became widespread in Western Europe. 19th-century Orientalism contributed to a certain popularity of Buddhism, and the 20th century brought increasing syncretism, New Age and various new religious movements divorcing spirituality from inherited traditions for many Europeans. The latest history brought increased secularisation, as well as religious pluralism.
According to Scholars, in 2017, Europe's population was 77.8% Christian (up from 74.9% 1970), these changes were largely result of the collapse of Communism and switching to Christianity in the former Soviet Union and Eastern Bloc countries.
Cultural influences.
Western culture, throughout most of its history, has been nearly equivalent to Christian culture, and many of the population of the Western hemisphere could broadly be described as cultural Christians. The notion of "Europe" and the "Western World" has been intimately connected with the concept of "Christianity and Christendom" many even attribute Christianity for being the link that created a unified European identity.
Though Western culture contained several polytheistic religions during its early years under the Greek and Roman empires, as the centralized Roman power waned, the dominance of the Catholic Church was the only consistent force in Europe. Until the Age of Enlightenment, Christian culture guided the course of philosophy, literature, art, music and science. Christian disciplines of the respective arts have subsequently developed into Christian philosophy, Christian art, Christian music, Christian literature etc.
Christianity had a significant impact on education and science and medicine as the church created the bases of the Western system of education, and was the sponsor of founding universities in the Western world as the university is generally regarded as an institution that has its origin in the Medieval Christian setting. Many clerics made significant contributions to science and Jesuits, in particular, made numerous significant contributions to the development of science. The Civilizing influence of Christianity (in Europe) includes social welfare, founding hospitals, economics politics, architecture, literature and family life.
Although the Protestant Reformation was a religious movement, it also had a strong impact on all other aspects of European life: marriage and family, education, the humanities and sciences, the political and social order, the economy, and the arts.
Denominations.
 Distribution of Christians in Europe by denomination
 ;templatestyles src="Legend/styles.css" / ;   Catholicism
 (46.3%) ;templatestyles src="Legend/styles.css" / ;   Eastern Orthodoxy
 (35.4%) ;templatestyles src="Legend/styles.css" / ;   Protestant
 (17.8%) ;templatestyles src="Legend/styles.css" / ;  Other (0.5%)
References.
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