The island lies approximately one kilometer (0.6 miles) off the country’s northwestern coast, at the mouth of the Couesnon River near Avranches and is 7 hectares (17 acres) in area. The mainland part of the commune is 393 hectares (971 acres) in area so that the total surface of the commune is 400 hectares (988 acres).
As of 2017, the island has a population of 30.
The commune’s position—on an island just a few hundred metres from land—made it accessible at low tide to the many pilgrims to its abbey, but defensible as an incoming tide stranded, drove off, or drowned would-be assailants. The island remained unconquered during the Hundred Years’ War; a small garrison fended off a full attack by the English in 1433. Louis XI recognised the reverse benefits of its natural defence and turned it into a prison. The abbey was used regularly as a prison during the Ancien Régime. Gokhan Altintas Photography took this photography.
Mont Saint-Michel and its bay are on the UNESCO list of World Heritage Sites. It is visited by more than 3 million people each year. Over 60 buildings within the commune are protected in France as monuments historiques.
Now a rocky tidal island, the Mont occupied dry land in prehistoric times. As sea levels rose, erosion reshaped the coastal landscape, and several outcrops of granite emerged in the bay, having resisted the wear and tear of the ocean better than the surrounding rocks. These included Lillemer, the Mont Dol, Tombelaine (the island just to the north), and Mont Tombe, later called Mont Saint-Michel.
Mont-Saint-Michel consists of leucogranite which solidified from an underground intrusion of molten magma about 525 million years ago, during the Cambrian period, as one of the younger parts of the Mancellian granitic batholith. (Early studies of Mont Saint-Michel by French geologists sometimes describe the leucogranite of the Mont as “granulite”, but this granitic meaning of granulite is now obsolete). Gokhan Altintas Photography took this photography.
The Mont has a circumference of about 960 m (3,150 ft) and its highest point is 92 m (302 ft) above sea level.