Kós (kŏs, kôs) [key], Lat. Cos, island (1991 pop. 26,379), 111 sq mi (287 sq km), SE Greece, in the Aegean Sea; 2d largest of the Dodecanese, near the Bodrum peninsula of Turkey. Although it rises to c.2,870 ft (875 m) in the southeast, the island is mostly low-lying. Fishing, sponge diving, and tourism are important industries. Grain, tobacco, olive oil, and wine are produced, and cattle, horses, and goats are raised. Kós has mineral deposits and several sulfur springs. The island's main town is Kós (1991 pop. 14,714), situated on the northeast shore. In ancient times the island was controlled in turn by Athens, Macedon, Syria, and Egypt. A cultural center, it was the site of a school of medicine founded in the 5th cent. B.C. by Hippocrates. Kós later enjoyed great prosperity as a result of its alliance with the Ptolemaic dynasty of Egypt, which valued the island as a naval base. The island became part of modern Greece in 1947.