Called the Isle of 20,000 Saints, Bardsey lies off the tip of the Lleyn peninsula, from which it is separated by the dangerous Bardsey Sound. The island is about 2 miles long by 3/4 mile broad. It contains the ruins of St. Mary's Abbey, which was founded in the sixth century. Hither fled the monks of Bangor Iscoed when they were threatened by a Northumbrian invasion, to make up the 20,000 saints who are supposed to have died on the island. As a result, Bardsey was for long a place of sacred pilgrimage.