Egyptian Christianity began in Alexandria, by far the greatest of the many cities founded by Alexander the Great. Jewish immigration into Egypt from Palestine had begun as early as the sixth century BCE, and Jews flowed into Alexandria in large numbers, with the result that the Alexandrian Jewish community became important in all of the diaspora. Christian organisation in Alexandria exhibits a continuity with Alexandrian Judaism, especially in the form of the presbyterate. Demetrius played a crucial role in the development of the Egyptian Christianity. The 'Catechetical School' of Alexandrian Christian tradition came into being only in the early third century as a result of the growing authority of bishop Demetrius. In the third century a new form of Gnosticism made its entry into Egypt, Manichaeism, which eventually became a world religion in its own right. Monasticism as an institution has played a greater role in the history of Egyptian Christianity than in that of any other regional church.