Loire, longest river of France, c.630 mi (1,010 km) long, rising in the Cévennes Mts., SE France, and flowing in an arc through central and W France to the Atlantic Ocean at Saint-Nazaire. The upper Loire swiftly flows northwestward through numerous gorges in the Massif Central. At Orléans it swings southwest and enters a wide fertile valley; Tours and Angers are there. In the Loire basin lie the rich fields, gardens, and vineyards of Orléanais, Touraine, and Anjou. At the head of the Loire estuary, c.35 mi (55 km) from the sea, is the industrial city of Nantes. The Loire's chief tributaries are the Allier, Cher, and Vienne. Silting, shallowness, and seasonal volume fluctuations limit the use of the Loire for navigation. Because the Loire is subject to heavy flooding, its banks are lined with dikes. The Loire Lateral Canal parallels the river from Roanne to Briare. Other canals connect the river with the Seine and Rhône river systems. The Loire valley has fostered traditions of civilized living that have become a heritage of all France. The châteaus of the Loire region are embodiments of French history and civilization.