According to Celtic mythology, Mont St-Michel was one of the sea tombs to which the souls of the dead were sent. Following his vision of St Michael, Bishop Aubert of Avranches built a devotional chapel at the summit of the island in 708. In 966, Richard I, duke of Normandy, gave Mont St-Michel to the Benedictines, who turned it into a centre of learning and, in the 11th century, into something of an ecclesiastical fortress, with a military garrison at the disposal of the abbot and the king.
In the 15th century, during the Hundred Years’ War, the English blockaded and besieged Mont St-Michel three times. The fortified abbey withstood these assaults; it was the only place in western and northern France not to fall into English hands. After the Revolution, Mont St-Michel was turned into a prison. In 1966 the abbey was symbolically returned to the Benedictines as part of the celebrations marking its millennium. Mont St-Michel and the bay became a Unesco World Heritage site in 1979.