Mont Saint-Michel. Le Mont-Saint-Michel is an island and mainland commune in Normandy, France. The island is located about one kilometer off the country's northwestern coast, at the mouth of the Couesnon River near Avranches and is 7 hectares in area. The mainland part of the commune is 393 hectares in area so that the total surface of the commune is 400 hectares. As of 2015, the island has a population of 50. 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. One of France's most recognisable landmarks, visited by more than 3 million people each year, Mont Saint-Michel and its bay are on the UNESCO list of World Heritage Sites. 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, 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. The Mont has a circumference of about 960 m and its highest point is 92 m above sea level. The tides can vary greatly, at roughly 14 metres between highest and lowest water marks. Popularly nicknamed St. Michael in peril of the sea by medieval pilgrims making their way across the flats, the mount can still pose dangers for visitors who avoid the causeway and attempt the hazardous walk across the sands from the neighbouring coast. Polderisation and occasional flooding have created salt marsh meadows that were found to be ideally suited to grazing sheep. The well-flavoured meat that results from the diet of the sheep in the pré salé makes agneau de pré-salé, a local specialty that may be found on the menus of restaurants that depend on income from the many visitors to the mount. The connection between the Mont Saint-Michel and the mainland has changed over the centuries. Previously connected by a tidal causeway uncovered only at low tide, this was converted into a raised causeway in 1879, preventing the tide from scouring the silt around the mount. The coastal flats have also been polderised to create pastureland, decreasing the distance between the shore and the island, and the Couesnon River has been canalised, reducing the dispersion of the flow of water. These factors all encouraged silting-up of the bay. On 16 June 2006, the French prime minister and regional authorities announced a €200 million project to build a hydraulic dam using the waters of the Couesnon and the tides to help remove the accumulated silt, and to make Mont Saint-Michel an island again. The construction of the dam began in 2009. The project also includes the removal of the causeway and its visitor car park. Since 28 April 2012, the new car park on the mainland has been located 2.5 kilometres from the island. Visitors can walk or use shuttles to cross the causeway. On 22 July 2014, the new bridge by architect Dietmar Feichtinger was opened to the public. The light bridge allows the waters to flow freely around the island and improves the efficiency of the now operational dam. The project, which cost €209 million, was officially opened by President François Hollande. On rare occasions, tidal circumstances produce an extremely high supertide. The new bridge was completely submerged on 21 March 2015 by the highest sea level for at least 18 years, as crowds gathered to snap photos. The original site was founded by an Irish hermit, who gathered a following from the local community. Mont-Saint-Michel was used in the sixth and seventh centuries as an Armorican stronghold of Gallo-Roman culture and power until it was ransacked by the Franks, thus ending the trans-channel culture that had stood since the departure of the Romans in 460.