Castelnaudary, a town of France, in the department of Aude, on the canal of Languedoc, 30 m. S. E. of Toulouse; pop. in 1866, 9,075. The reservoir of St. Ferriol forms a harbor, and an active trade is carried on in cereals, wine, fruit, cloth, linen, silk, cotton yarn, leather, and other articles. According to some authorities, the ancient Sostomagus was situated near Castelnaudary, the modern name being a corruption of Castrum Novum Aria-norum, as the new town was called after the old one had been destroyed in the 5th century. It became the fortified capital of the county of Lauragais, ruled by the counts of Toulouse. It suffered severely during the crusade against the Albigenses, and in 1211 was the scene of a battle between Raymond of Toulouse and Simon de Montfort, the former of whom destroyed the fortifications in 1229. In 1237 an auto da fe was enacted here, in which many persons accused of heresy were put to death. It was burned in 1355 by Edward the Black Prince, but was rebuilt in 1366. In September, 1632, the duke of Montmorency, commanding the forces of Gaston of Orleans, was defeated here by the royal force under Marshal Schornberg, wounded, taken prisoner, and executed.