Síros (sēˈrôs) [key] or Syros sĪˈrŏs, island (1991 pop. 19,870), 33 sq mi (85 sq km), SE Greece, in the Aegean Sea, one of the Cyclades. Ermoupolis, or Síros, is the island's main town and port. Síros is the richest and most populous of the Cyclades. During the Greek War of Independence (1821–29) the island remained neutral, and many Greeks took refuge on it. By the mid-19th cent. the island had considerable commercial importance. It is also known as Syra.