CALATAYUD, a city of central Spain, province of Sara gossa. It lies on the left bank of the river Jalon, just below the entrance of its tributary the Jiloca, and is served by the Madrid Saragossa and Calatayud-Sagunto railways. Pop. (193o) 15,168. Calatayud consists of a lower more modern and well-built town, and an upper or Moorish town, where there are many rock-hewn dwellings inhabited by the poorer classes. Two collegiate churches are especially noteworthy. Santa Maria, originally a mosque, has a lofty red octagonal tower and a fine Renaissance doorway, added in 1528; while Santo Sepulcro, built in 1141, and restored in 1613, was long the principal church of the Spanish Knights Templar. Commercially Calatayud ranks second only to Sara gossa among the Aragonese towns, for it is the central market of the exceptionally fertile valleys of the Jalon and Jiloca. About 2m. E. are the ruins of the ancient Bilbilis where the poet Martial was born (c. A.D. 4o). This town was celebrated for its breed of horses, its armourers, its gold and its iron. Destroyed by the Arabs in the 8th century, its ruins later provided stone for the building of Calatayud, whose name is an adaptation of the Moorish Kalat Ayub, "Castle of Ayub."