Inishmurray may be named after the early saint, Muiredach mac Echdach (fl. early 6th century) of Killala. There are remains of an early Irish monastic settlement. Laisrén (Saint Molaise) Mac Decláin reputedly founded a monastery here in the 6th century. He was confessor of Saint Columba (Colmcille) after the Battle of Cúl Dreimhne on the mainland nearby.
The island's ecclesiastical settlement was attacked in 795 and again in 807 by the Vikings, and eventually the monks abandoned the island and it remained uninhabited until the first secular settlement, probably in the 12th century.
The enclosure wall is impressive - reaching 4.5 metres in height at its highest point and up to 3 metres thick. The site contains various ecclesiastical buildings including enclosures, a stone-roofed oratory, two churches, a clochán, a large beehive-shaped cell, a holy well and other remains including cross slabs suggesting foreign influences. The whole complex is composed of what is probably local sandstone rubble.
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Saint-Georges de Boscherville Abbey is a former Benedictine abbey. It was founded in about 1113 by Guillaume de Tancarville on the site of an earlier establishment of secular canons and settled by monks from the Abbey of Saint-Evroul. The abbey church made of Caumont stone was erected from 1113 to 1140. The Norman builders aimed to have very well-lit naves and they did this by means of tall, large windows, initially made possible by a wooden ceiling, which prevented uplift, although this was replaced by a Gothic vault in the 13th century. The chapter room was built after the abbey church and dates from the last quarter of the 12th century.
The arrival of the Maurist monks in 1659, after the disasters of the Wars of Religion, helped to get the abbey back on a firmer spiritual, architectural and economic footing. They erected a large monastic building one wing of which fitted tightly around the chapter house (which was otherwise left as it was).