The Doubs (French pronunciation: ​[du], German: Dub) is a 453 kilometres (281 mi) long river in eastern France and western Switzerland, left tributary of the Saône. Its source is near Mouthe in the western Jura mountains.First it flows northeast, more or less along the French-Swiss border (forming the border for approx. 40 km). Near Montbéliard it turns southwest, until it flows into the river Saône in Verdun-sur-le-Doubs, approx. 20 km northeast of Chalon-sur-Saône.