The Somme is a river in Picardy, northern France. The name Somme comes from a Celtic word meaning “tranquility”. The department Somme was named after this river.

The river is 245 km (152 mi) long, from its source in the high ground of the former Forest of Arrouaise at Fonsommes near Saint-Quentin, to the Bay of the Somme, in the English Channel. It lies in the geological syncline which also forms the Solent. This gives it a fairly constant and gentle gradient where several fluvial terraces have been identified.