Christianity was introduced in the 5th century. This is traditionally associated with St. Patrick although there were some Christians in the country before his arrival. The first written documents date from this period. A distinctive feature of the development of early Irish Christianity was the important role played by monasticism. The great monasteries such as Glendalough, founded by St. Kevin, and Clonmacnoise, founded by St. Ciaran, were famous centers of culture and learning and the illuminated manuscripts that they produced were among the glories of Irish monasticism.
It was through the monasteries that Irish influence on Britain and Europe was exerted from the 6th century onwards. Setting out first as pilgrims, Irish monks preached the Gospel and established new communities across the continent. Ireland, unlike most of the rest of Europe, did not suffer barbarian invasion and so acted as a repository of Christian civilization at a time when it was almost extinguished elsewhere. Irish monks are associated with a number of continental centers – St. Fursey at Peronne in France, St. Kilian at Wurzburg in Germany, St. Vergil at Salzburg inAustria, St. Columbanus at Bobbio in Italy. They brought Christianity to pagan peoples, established centers of learning and paved the way for the intellectual flowering in 9thcentury France known as the Carolingian Renaissance. One of the most notable of these monks was the philosopher and theologian Johannes Scotus Eriugena.
The successful missionary efforts of the Irish abroad were matched by rich cultural achievements at home. Elaborate chalices, crosiers and ornamental jewelry were fashioned while the scribes committed the rich classical tradition to their magnificently illuminated manuscripts. This period from the 6thto the 9th century has been seen by many as the Golden Age of Irish history.