There is a clear faith-based division in the Mediterranean region today. The north, from Portugal to Greece, is mostly Christian. The south, from Morocco to Egypt, is mostly Muslim. The east, which includes Turkey and the countries of the so-called Levant, is largely Muslim with sizable pockets of Christians and Jews. Europe purged itself of Islam centuries ago and has sought to uphold a monoreligious culture ever since; the Islamic side has rarely uprooted its native Christian populations, although it has not always treated them fairly.
The division was not as neat in medieval times. The two sides intermingled in ways that render any projection of the present split into the past difficult to sustain. Christians were numerous in the Islamic countries, and Europe had Islamic dominions in all of its southern edges. We are all familiar with the cultural achievements of the Muslims (the Moors of yesteryear) in Iberia...
University of California Press