Mont Saint-Michel is a rocky tidal island and a commune in Normandy, France. It is located approximately one kilometre (just over half a mile) off the country's north-western coast, at the mouth of the Couesnon River near Avranches. The population of the island is 41, as of 2006. The island has been a strategic point holding fortifications since ancient times, and since the 8th century AD it became the seat of the Saint-Michel monastery, from which it draws the name.
In prehistoric times the bay was land. As sea levels rose, erosion shaped the coastal landscape over millions of years. Several blocks of granite or granulite 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 was previously connected to the mainland via a thin natural land bridge, which before modernization was covered at high tide and revealed at low tide.