CASTELNAUDARY, the chief town of an arrondissement in the department of Aude, in France, 21 miles northwest of Carcassonne. It is finely situated on an elevation in the midst of a fertile and well-cultivated plain; and its commercial facilities are greatly increased by the Canal du Midi, which widens out, as it passes the town, into an extensive basin or reservoir, surrounded with wharves and warehouses. The principal buildings are the courthouses, the church of St Michel, the exchange, and the communal college. There are large manufactures of woollen and cotton goods, linen, leather, bricks, tiles, and earthenware; an extensive trade is maintained in lime, gypsum, grain, fruits, and wine; and the building of canal boats forms an important industry. By some authorities Castelnaudary is supposed to represent the ancient Sostomagus, and to receive its present name, which they regard as a corruption of the Latin Castrum Novum Arianorum, from the fact that it was rebuilt by the Visigoths, who were adherents of the Arian party. It is distinctly mentioned in the 12th century, and in 1212 it was remarkable as the scene of a great conflict between the counts of Toulouse and Foix and Simon de Montfort, in which the former were defeated. In 1229 the town was deprived of its ramparts; and in 1355 it was captured and burned by the Black Prince. In 1632 the duke of Montmorency was defeated here by the royal troops under Schomberg. Population in 1872, 7946.