Batz-sur-Mer is a commune in the Loire-Atlantique department in western France.The commune is situated on a former island that, until around the 9th century, was separate from the mainland at Guérande and the neighboring island of Le Croisic. The territory of the commune is now part of the wild coast of Guérande Peninsula with rocky cliffs, sandy beaches along the Atlantic Ocean, and a extensive salt marshes to the northeast and east.The town lies between the Bay of Biscay and its salt marshes and is a very Breton town of whitewashed granite houses.HistoryIn 945, Alan II, Duke of Brittany, founded a priory in Batz-sur-Mer, dedicated to St Winwaloe. Its Benedictine monks developed the local economy, and apart from religion they devoted themselves to agriculture and to the maintenance of salt ponds.The historic church of Saint-Guénolé, or Winwaloe, largely dating from the 15th century, stands in the town centre. The church contains a 16th-century sculpture of the Madonna and Child, and its 17th-century belfry provides a significant local landmark. Climbing to the top of the tower gives a good view over the salt marshes and the Le Croisic peninsula.