Seine (Sayn or Sehn), one of the four chief rivers of France, rises on the slope of the plateau of Langres, north-west of Dijon, and winds 482 miles NW., past Troyes, Fontainebleau, Melun, Paris, St Denis, St Germain, Mantes, Elbeuf, and Rouen, till it falls into the English Channel by a wide estuary, on which stand the ports of Har-fleur, Havre, and Honfleur. It is navigable for boats from Marcilly, 350 miles from its mouth, and since 1890 the canalisation of the Seine has been one of two projects (the other a ship-canal) for connecting Paris with the Atlantic. The Seine receives the Aube, Marne, and Oise from the right, and the Yonne, Loing, Essonne, and Eure from the left; and is connected by canals with the Somme, Scheldt, Meuse, Rhine, Saone, and Loire. Works for keeping open a navigable channel through the estuary, which is liable to silt up, were carried out in 1848-70; by these 28,000 acres of land have been reclaimed, and vessels of 2000 tons, drawing 20 feet of water, can get up to Rouen. A canal connects Havre with the Seine at Tancarville.
Seine, the metropolitan dep. of France, completely enclosed by the dep. of Seine-et-Oise, is a portion of the former province of lle-de-France. One-sixth of its area is covered by the city of Paris (q.v.), and the rest is thickly studded with the suburban villages of the capital - Boulogne, Puteaux, Clichy, Montreuil, etc. It is at once the smallest and the most populous dep. in the republic: its area is 185 sq. m.; its pop. in 1876 was 2,410,849, and in 1901, 3,669,930. The arrondissements are Paris, St Denis, and Sceaux.