CASTELSARRASIN, a town of south-western France, capital of an arrondissement in the department of Tarn-et-Garonne, 12 m. W. of Montauban on the Southern railway. Pop. (1906) town, 3189; commune, 7496. Castelsarrasin, situated on the left bank of the lateral canal of the Garonne and about a mile from the right bank of that river, is surrounded by promenades occupying the site of the old fortifications. Its chief building is the brick-built church of St Sauveur, which dates from the 13th century. The administrative buildings are modern. The town has a sub-prefecture, a tribunal of first instance, and a communal college. The principal industrial establishment is the metal-foundry of Sainte-Marguerite, where copper, tin and other metals are worked; there are also flour-mills, saw-mills and dye-works. Trade is in cattle, agricultural produce, wine, baskets and game.
The name Castelsarrasin appears in the 13th century, when the village of Villelongue was replaced by the present bastide. Castrum Cerrucium, Castel-sur-Azine (from the neighbouring stream, Azine) and Castellum Sarracenum are suggested derivations, no one of which can be adopted with certainty.