Now a rocky tidal island, in prehistoric times the Mont was on dry land. As sea levels rose, erosion reshaped the coastal landscape, and several outcroppings 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. The Mont has a circumference of about 960 metres (3,150 ft), and is 92 metres (302 ft) above sea level at its highest point