JACA, or JACCA, a fortified town of Spain, in the province of Aragon, situate at the foot of the Pyrenees, on the River Aragon, 60 miles N. of Saragossa, and about 20 miles distant from the French frontier. It is a town of great antiquity, and, from its position, has been the scene of many sanguinary contests. Its occupation was eagerly coveted by every invader of the peninsula, from Cato and Julius Caesar to the generals of Napoleon. Jaca is the see
of a bishop, who is suffragan to the archbishop of Saragossa. It is well built, and possesses an old cathedral, with several religious houses. The remains of an old Roman wall are still visible amongst its other defences. Pop. about 3200.