Mont Saint-Michel

Mont Saint-Michel rises as a granite islet in a bay famous for tidal ranges of up to 14 metres — among the largest in Europe — which historically isolated the island at high tide and connected it to the mainland by a sand causeway at low tide, a natural defence that allowed the abbey to remain unconquered during the Hundred Years' War despite repeated English sieges. According to tradition recorded in the 9th-century chronicle Revelatio Ecclesiae Sancti Michaelis, the Archangel Michael appeared to Aubert, Bishop of Avranches, in 708 CE, instructing him to build a sanctuary on the island; Aubert ignored the vision twice before the Archangel, on a third appearance, supposedly burned a hole through the bishop's skull with his finger to ensure compliance — a relic skull with a hole, displayed in the treasury of the Church of Saint-Gervais in Avranches, is presented as physical evidence of the event.

The abbey grew over the following centuries into a major pilgrimage site and a fortified monastery of the "Marvel" (La Merveille), a Gothic architectural ensemble added in the 13th century. During the French Revolution it was converted into a prison, holding political prisoners until 1863. A causeway built in 1879 ended the island's tidal isolation but caused silting of the bay; a major hydraulic engineering project completed in 2015, including a new bridge and a dam to flush sediment, restored the island's maritime character, and Mont Saint-Michel is now an island again only at the highest tides.