Numidia, ancient Roman name for that part of northern Africa roughly equivalent to modern Algeria. Numidia was inhabited by two tribes noted for their horsemanship. In the Second Punic War (218-201 bc) between Carthage and Rome the western tribe of Numidians supported Hannibal, the leader of Carthage. Masinissa, king of the eastern Numidians, joined the Romans. With the victory of Rome, all Numidia was united under Masinissa's rule. The most famous of his successors were Jugurtha and Juba I. After the victory of Julius Caesar over Juba in the African war, Numidia became (46 bc) a Roman province called Africa Nova. In 30 bc the Roman emperor Augustus restored the western part of Numidia to Juba II (died ad19), and five years later the eastern part was united with Africa Vetus to form the province of Africa. Under Emperor Septimius Severus (reigned 193-211), Numidia once more became a separate province. The country was conquered by the Vandals in the 5th century and the Arabs in the 8th century; it remained under Arab control until the French conquest of Algeria in the 19th century.