The Loire River (in French) is the longest river in France. With a length of , it drains an area of , which represents more than a fifth of France's land area. It rises in the Cévennes Mountains in the Département of Ardèche at 1,350 m/4,430 ft near Mont Gerbier de Jonc, and flows for over north through Nevers to Orléans, then west through Tours and Nantes until it reaches the Bay of Biscay at St Nazaire. Its main tributaries include the Maine River, Nièvre River and the Erdre River on the right bank, and the Allier River, Cher River, Indre River, Vienne River, and the Sèvre Nantaise River on the left bank. The Loire gives its name to the départements of Loire, Haute-Loire, Loire-Atlantique, Indre-et-Loire, Maine-et-Loire, and Saône-et-Loire. The central part of the Loire Valley was added to the World Heritage Sites list of UNESCO on December 2, 2000. The banks are characterised by vineyards and chateaus in the Loire Valley.
In French the adjective derived from the river is ligérien, as in le climat ligérien ("the climate of the Loire Valley"), a climate considered the most pleasant of northern France, with warmer winters and, more generally, fewer extremes in temperatures, rarely exceeding .
Studies of the paleogeography of the region suggest that in the Pleistocene the paleo-Loire continued its northward flow and joined the Seine, while the lower Loire found its source upstream of Orléans in the region of Gien, flowing westward along the present course. At a certain point during the long history of uplift in the Paris Basin, the lower, Atlantic Loire captured the "paleo-Loire" or Loire séquanaise ("Loire-Seine"), producing the present river. The former bed of the Loire séquanaise is occupied by the Loing.
Unlike most other rivers in western Europe, there are very few dams or locks creating obstacles to its natural flow. The Villerest dam, built in 1985 a few kilometers south of Roanne, has played a key-role in preventing recent flooding. As a result, the Loire is a very popular river for boating excursions, flowing through a pastoral countryside, past limestone cliffs and historic castles.
The Phoenicians and Greeks had used packhorses to transport goods from Lyon to the Loire to get from the Mediterranean basin to the Atlantic coast. The Romans used the Loire as far as Roanne, only around from the source, whilst the Vikings used longships to attack Tours.
River traffic increased until the 19th century, with a toll system being used in medieval times. For centuries attempts were made to keep a navigable channel open by the use of wooden embankments and dredging. During the 17th century, Jean-Baptiste Colbert instituted stone retaining walls and quays from Roanne to Nantes which helped make the river more reliable, but navigation was frequently stopped by flood and drought. In 1707 floods were said to have drowned 50,000 people, with the water rising more than in two hours in Orléans. A typical passenger timetable from Orléans to Nantes took eight days, with the upstream journey against the flow taking fourteen.
Steam-driven passenger boats appeared soon after the beginning of the 19th century plying the river between Nantes and Orléans; by 1843, 70,000 passengers were being carried annually in the lower river. However with the introduction of the railway in the 1840s trade on the river steadily declined and proposals to build a fully navigable river up to Briare came to nothing. The opening of the Canal latéral à la Loire in 1838 enabled navigation between Digoin and Briare to continue, but the river level crossing at Briare remained a problem until the construction of the Briare aqueduct in 1896.
The Canal de Roanne à Digoin was also opened in 1838 and was nearly closed in 1971 but still provides navigation further up the Loire valley to Digoin. However the Canal de Berry, a narrow canal with locks only wide, which was opened in 1820s and connected the Canal latéral à la Loire at Marseilles-lès-Aubigny to the Cher River at Noyers and back into the Loire near Tours, was closed in 1955.
Several départements of France were named after the Loire. The Loire flows through the following départements and towns: