The whole period of the next five centuries was dominated by the struggle between Christianity and Islam throughout the Mediterranean Basin.The battles of Poitiers, and Toulouse preserved the Catholic west, even though Rome itself was ravaged in 850, and Constantinople besieged.This council affirmed that Gentiles could become Christians without adopting all of the Mosaic Law.
In the east, the Byzantine Empire preserved Orthodoxy, well after the massive invasions of Islam in the mid-7th century.
The invasions of Islam devastated three of the five Patriarchal sees, capturing Jerusalem first, then Alexandria, and then finally in the mid-8th century, Antioch.
Christianity spread throughout the early Roman Empire, despite persecutions due to conflicts with the pagan state religion.
In 313, the struggles of the Early Church were lessened by the legalisation of Christianity by the Emperor Constantine I.
Conditions in the Roman Empire facilitated the spread of new ideas.