SOMME, a department of northern France, formed in 1790 of a large part of the province of Picardy (comprising Vermandois, Santerre, Amiénois, Ponthieu, Vimeu, and Marquenterre) and a small portion of Artois. Pop. (1906), 532,567. Area 2423 sq. m. It is bounded on the N. by Pas-de-Calais, E. by Aisne, S. by Oise, and S.W. by Seine-Inférieure, and its sea-coast extends 28 m. along the English Channel. Two streams flowing into the Channel—the Authie on the north and the Bresle on the south-west—bound it in these directions. The surface consists of great rolling plains, generally well cultivated and very fertile. The highest point, about 700 ft. above the sea, lies in the south-west, not far from Aumale. From the mouth of the Authie to the Bay of the Somme the coast is lined with a belt of sand dunes about 2 m. broad, behind which is the Marquenterre, a tract of 50,000 acres reclaimed from the sea by means of dykes and traversed by drainage canals. The Bay of the Somme, obstructed by dangerous sandbanks, contains the three fishing ports of Crotoy, St Valery, which is also the chief commercial port, and Le Hourdel. Next come the shingle banks, behind which the low fields of Cayeux (25,000 acres) have been reclaimed; and then at the hamlet of Ault commence the chalk cliffs, which continue onwards into Normandy.
The river Somme rises to the N.N.E. of St Quentin in the department of Aisne, where it has a course of about 25 m.; it traverses the department of Somme from the south-east to the north-west for a distance of about 125 m., through a marshy valley abounding in peat. Commanded by Ham, Péronne, Amiens and Abbeville, this valley forms a northern line of defence for Paris. Apart from the water-power it supplies, the Somme is of great commercial value, being accompanied by a canal all the way from its source wherever it is not itself navigable. From Abbeville to St Valery its lower course forms a maritime canal 165 ft. wide, 12 ft. deep, and 8 to 9 m. long, capable of bearing at high tide vessels of 300 tons burden. From St Valery to the open sea the current hollows out a very variable bed accessible at certain tides for vessels of 500 tons. The most important affluents of the Somme—the Ancre from the north-east by way of Albert and Corbie, the Avre from the south-east by Roye, and the Selle from the south by Conty—join the main streams at Amiens. The Authie and the Bresle are respectively 63 and 45 m. long. The latter ends in a maritime canal about 2 m. long between Eu and Tréport.
The mean temperature is lower than that of Paris (49° F. at Abbeville). The mean annual rainfall is 33 in. at Abbeville. The department, especially in the north-east, is one of the best cultivated in France. Beetroot for sugar is the staple crop of the Péronne arrondissement; cereals, chiefly wheat, fodder and mangel-wurzels, oil plants, poppy, colza, flax, hemp and potatoes are grown throughout the department, the latter more largely on the seaboard. Stock-raising of all kinds is successfully carried on. No wine is grown, the principal drinks being beer and cider. Market gardening is of great importance round Amiens. Peat-cutting is actively carried on, the best qualities and the deepest workings being in the valley of the Somme, between Amiens and Abbeville. Phosphate of lime is also an important mineral product. The manufacture of a great variety of textile goods, especially velvet (Amiens), of beet sugar and alcohol, and of locks, safes and the like (in the Vimeu), are characteristic industries of the department, which also carries on saw-milling, flour-milling, brewing, dyeing, ironfounding and forging, printing and the manufacture of paper, chemical products, machines and ironmongery, hosiery (in the Santerre), &c. Cereals, horses of the Boulogne or Norman breed, cattle, hemp and linen, and the manufactured goods are the exports of the department. St Valery (pop. 3389) exports vegetables and farm-products (to England), and shingle for the manufacture of earthenware. Besides the raw materials for the manufacturing industries, wines and timber, the latter largely imported at St Valery, dyestuffs and coal are imported.
The department is served principally by the Northern railway, and its canals and rivers provide 140 m. of navigable waterway. Administratively the department comprises 5 arrondissements (those of Amiens, the capital, Abbeville, Doullens, Montdidier and Péronne), 41 cantons and 836 communes. The department belongs to the académie (educational circumscription) of Lille, and constitutes the diocese of Amiens, which city is also the seat of a court of appeal and the headquarters of the region of the II. army corps, wherein the department is included.
The most noteworthy places are Amiens (the capital), Abbeville, Montdidier, Péronne, Doullens, St Riquier, Crécy and Ham, which are treated under those headings. The following places may also be mentioned: Albert (pop. 6656), after Amiens and Abbeville the most populous town in the department and a centre for machine construction; Villers-Bretonneux (pop. 4447), a centre of hosiery manufacture; Corbie, once celebrated for its Benedictine abbey (founded in the 7th century) the church of which (16th–18th century) is still to be seen; L'Étoile, with the well-preserved remains of a Roman camp; Folleville, which has a church (15th century) containing the fine Renaissance tomb of Raoul de Lannoy; Picquigny, with the remains of a château of the 14th, 15th and 16th centuries, once one of the chief strongholds of Picardy; Rue, where there is a fine chapel of the 15th century; and Tilloloy, which has a Renaissance church.