LOIRE, lwiir (Lat. Ligcr). The longest river of France (Slap: France, 4). It rises in the Cevennes in the Department of Ardeche at an altitude of about 4500 feet. and flows in a northern direction partly through a mountainous region to its junction with the Allier (q.v.). near Nevers„ where it turns northwest and main tains that direction to Orleans. From there it flows southwest to Tours, and the rest of its course runs in a general westerly direction. emptying into the Atlantic by a wide estuary at Saint Nazaire. Its total length is over 620 miles, and its basin occupies nearly one-fourth of time area of France. Its chief tributaries are the Allier, Cher. Indre, Vienne, and Thouet, from the left. and the Arroux and the Maine, which is formed by the union of the Sarthe and Slayenne from the right. Only the estuary of the Loire front the sea to Nantes (31 miles) is accessible to sea ves sels, hut boats ascend as far as Roannes, about 490 miles from the mouth. Navigation is greatly
impeded by the insufficient depth of the river at certain periods of the year. The melting of the snow in the mountains and rains cause a rise in the tributaries of the Loire with the result that the main stream swells to many times its usual volume, not infrequently overflowing its banks with disastrous results. To guard against these floods, dikes were constructed along the river as early as the Middle Ages. In the first half of the nineteenth century a canal about 125 miles long was constructed along the river to provide a reservoir for the overflowing water. Canals also connect the Loire with the Sa.5ne and the Seine, and there is a canal connecting Nantes with the harbor of Brest.