Christianity is a religion based on the life and teachings of Jesus of Nazareth, as described in the New Testament. Its adherents, known as Christians, believe that Jesus Christ is the Son of God and savior of all people, whose coming as the Messiah was prophesied in the Old Testament.
Depending on the specific denomination of Christianity, practices may include baptism, Eucharist (Holy Communion or the Lord's Supper), prayer (including the Lord's Prayer), confession, confirmation, burial rites, marriage rites and the religious education of children. Most denominations have ordained clergy and hold regular group worship services.
Christianity developed during the 1st century CE as a Jewish Christian sect of Second Temple Judaism. It soon soon also attracted Gentile God-fearers, which lead to a departure from Jewish customs, and the establishment of Christianity as an independent religion. During the first centuries of its existence Christianity spread throughout the Roman Empire, and also to Ethiopia, Transcaucasia, and some parts of Asia.
Constantine the Great converted to Christianity and decriminalized it via the Edict of Milan (313). The First Council of Nicaea (325) established a uniform set of beliefs across the Roman Empire. By 380, the Roman Empire designated Christianity as the state religion. The period of the first seven ecumenical councils is sometimes referred to as the Great Church, the united full communion of the Roman Catholic Church, Eastern Orthodox Church, and Oriental Orthodoxy, before their schisms.
Oriental Orthodoxy split after the Council of Chalcedon (451) over differences in Christology. The Eastern Orthodox Church and the Catholic Church separated in the East–West Schism (1054), especially over the authority of the Pope. Similarly, in 1521, Protestants were excommunicated from the Roman Catholic Church in the Protestant Reformation over Papal primacy, the nature of salvation, whether it was permissible to burn heretics, and other ecclesiological and theological disputes.
There are 2.3 billion Christians in the world, or 31.4% of the global population. Today, the four largest branches of Christianity are the Catholic Church (1.3 billion), Protestantism (920 million), the Eastern Orthodox Church (260 million) and Oriental Orthodoxy (86 million).