DAX, AX, or AGS (Aqua Tarbellica), an ancient town of France, department of Landes, capital of the above arrondissement, situated in a fertile plain on the left bank of the Adour, 32 miles S.W. of Mont-de-Marsan. It is surrounded by old walls flanked with towers, and has a cathedral, episcopal palace, hall of justice, prison mineralogical museum, agricultural society, &c. It possesses numerous thermal medicinal springs. Manufactures—earthenware, pitch, oil,
thread, leather, &c.; and it has some trade in corn, wine, brandy, and wood. Pop. 5238. Before the Roman conquest of Gaul, Dax was the capital of the Tarbellii.