Cá·diz (kə-dĭz', kā'dĭz, kä'-, kä'thēth, -thēs) A city of southwest Spain northwest of Gibraltar on the Gulf of Cádiz, an inlet of the Atlantic Ocean. Cádiz was founded c. 1100 B.C. by Phoenicians and passed to the Carthaginians (c. 500 B.C.), Romans (third century A.D.), Moors (711), and the kingdom of Castile (1262). Its port was a base for Spanish treasure ships after the conquest of the Americas. Population: 129,000.