A watering place of south-western France, in the department of Ariege, at the confluence of the Ariege with three tributaries, 26 m. S.S.E. of Foix by rail. Pop. (1906) 1179. Ax (Aquae), situated at a height of 2300 ft., is well known for its warm sulphur springs (77°-172° F.), of which there are about sixty. The waters, which were used by the Romans, are efficacious in the treatment of rheumatism, skin diseases and other maladies.