The first Christians called themselves followers of The Way; outsiders coined Christian
Jesus's earliest followers were Jews who saw no new religion in what they were doing, and they described their movement as The Way. The label Christian came from non-Jewish residents of Antioch. From that sect in Roman Judaea grew the world's largest faith, with more than 2.3 billion adherents today.
The first community gathered in Jerusalem under three leaders remembered as the Pillars, James the Just, Peter and John, waiting for Jesus to return. They interpreted him through Jewish messianic and apocalyptic ideas and remained part of Jewish religious life. What happened to that original group is unclear; it may have scattered or perished when Rome destroyed Jerusalem in 70 AD. The oldest known use of the word Christianity is by Ignatius of Antioch around 100 AD.
The decisive shift came with Gentiles. Paul, a Pharisee who had once persecuted the movement, argued that non-Jews could share in Israel's promises through faith in Christ and baptism without keeping the full Torah, including circumcision. That opened the door to the Greco-Roman world and slowly separated the two faiths, a split visible by the second century. Early Christianity was also far from unified. Marcion of Sinope taught that the good father of Christ differed from the merely just god of Israel and assembled one of the first Christian scripture collections, while Valentinus offered a Gnostic path of saving knowledge. Rival writers began using hairesis, school of thought, which became heresy.
Persecution was sporadic and local until 249, when Emperor Decius ordered everyone except Jews to sacrifice to Rome's gods; the campaign launched under Diocletian in 303 was harsher still. Armenia's King Tiridates III made it the first officially Christian state early in the fourth century. When Constantine legalised the faith in 313, Christians were perhaps only 5 percent of the Roman population, and by 380 Nicene Christianity was the imperial state church.
Later ruptures produced today's branches: Catholics number about 1.3 billion, Protestants 800 million and Eastern Orthodox 300 million. Christians form a majority in an estimated 120 countries and territories, the faith is expanding in Africa and Asia, and it is declining in parts of the West, where about 70 percent still identify with it.
Source: Christianity
