Christianity arose in Roman-ruled Judaea, around the teaching of Jesus of Nazareth and the first followers who regarded him as the messiah. It began as a current within Judaism; its early opening to non-Jews was one of the turning points that made it a separate religion. In the first centuries the movement was scattered, at times illegal, and under pressure.

Several factors eased its spread: the rapid circulation of ideas via the Roman road network and a shared language, organization within urban communities, and a universal message of salvation. In the fourth century the Roman state first granted tolerance and then adopted the religion; this carried Christianity from a minority movement to the dominant faith of the empire.

The formation of the texts, the divergent interpretations, and the earliest dates are debated; there is no single founding moment but a gradual emergence. Its impact was not confined to religion: law, the calendar, art, educational institutions, and notions of political legitimacy were shaped through this tradition for centuries. Much of subsequent European and Mediterranean history is read within this frame.