<P> By around 800 they were producing illuminated manuscripts such as the Book of Kells . The missions of Gaelic monasteries led by monks like St Columba spread Christianity back into Western Europe during the Middle Ages, establishing monasteries initially in northern Britain, then through Anglo - Saxon England and the Frankish Empire during the Middle Ages . Thomas Cahill, in his 1995 book How the Irish Saved Civilization, credited Irish Monks with having "saved" Western Civilization during this period . According to art historian Kenneth Clark, for some five centuries after the fall of Rome, virtually all men of intellect joined the Church and practically nobody in western Europe outside of monastic settlements had the ability to read or write . </P> <P> Around AD 500, Clovis I, the King of the Franks, became a Christian and united Gaul under his rule . Later in the 6th century, the Byzantine Empire restored its rule in much of Italy and Spain . Missionaries sent from Ireland by the Pope helped to convert England to Christianity in the 6th century as well, restoring that faith as the dominant in Western Europe . </P> <P> Muhammed, the founder and Prophet of Islam was born in Mecca in AD 570 . Working as a trader he encountered the ideas of Christianity and Judaism on the fringes of the Byzantine Empire, and around 610 began preaching of a new monotheistic religion, Islam, and in 622 became the civil and spiritual leader of Medina, soon after conquering Mecca in 630 . Dying in 632, Muhammed's new creed conquered first the Arabian tribes, then the great Byzantine cities of Damascus in 635 and Jerusalem in 636 . A multiethnic Islamic empire was established across the formerly Roman Middle East and North Africa . By the early 8th century, Iberia and Sicily had fallen to the Muslims . By the 9th century, Malta, Cyprus, and Crete had fallen--and for a time the region of Septimania . </P> <P> Only in 732 was the Muslim advance into Europe stopped by the Frankish leader Charles Martel, saving Gaul and the rest of the West from conquest by Islam . From this time, the "West" became synonymous with Christendom, the territory ruled by Christian powers, as Oriental Christianity fell to dhimmi status under the Muslim Caliphates . The cause to liberate the "Holy Land" remained a major focus throughout medieval history, fueling many consecutive crusades, only the first of which was successful (although it resulted in many atrocities, in Europe as well as elsewhere). </P>

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