and Christian religion survived in an increasingly Hellenised form in the Byzantine Empire centered at Constantinople in the East, Western civilization suffered a collapse of literacy and organization following the fall of Rome in AD 476. Gradually however, the Christian religion re-asserted its influence over Western Europe. After the Fall of Rome, the papacy served as a source of authority and continuity. In the absence of a magister militum living in Rome, even the control of military matters fell to the pope. Gregory the Great (c 540–604) administered the church with strict reform. A trained Roman lawyer and administrator, and a monk, he represents the shift from the classical to the medieval outlook and was a father of many of the structures of the later Roman Catholic Church. According to the Catholic Encyclopedia, he looked upon Church and State as co-operating to form a united whole, which acted in two distinct spheres, ecclesiastical and secular, but by the time of his death, the papacy was the great power in Italy: According to tradition, it was a Romanized Briton, Saint Patrick who introduced Christianity to Ireland around the 5th century. Roman legions had never conquered Ireland, and as the Western Roman Empire collapsed, Christianity managed to survive there. Monks sought out refuge at the far fringes of the known world: like Cornwall, Ireland, or the Hebrides. Disciplined scholarship carried on in isolated outposts like Skellig Michael in Ireland, where literate monks became some of the last preservers in Western Europe of the poetic and philosophical works of Western antiquity. 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. 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