river, northern France. It rises in the hills at Fonsommes, near Saint-Quentin in the Aisne département, and flows generally westward for 152 miles (245 km) to the English Channel, crossing Somme département and the ancient province of Picardy. From Amiens, near which its headstreams (including the Ancre and Avre) converge, the Somme follows the floor of a trench across the chalk country. Its valley is a marshy belt; and its line, an important barrier in the approaches from Flanders toward Paris, was of great strategic importance during World War I. The name Somme is derived from the Celtic samara, meaning “tranquil.” The upper basin of the Somme was the scene of heavy fighting during World War I, particularly the First Battle of the Somme (July–November 1916). The valley was occupied by the Germans in May–June 1940 in World War II and was recovered by the Allies in August 1944.

The basin of the Somme River occupies about 2,300 square miles (6,000 square km). Below Abbeville the Somme enters a sand-encumbered estuary, which requires constant dredging, with the port of Saint-Valéry-sur-Somme situated at its mouth. From the river's upper valley there are canals to the Oise and the Escaut, or Scheldt, rivers, connecting it with the navigable waterways that link Paris and Flanders.