Póros (pôˈrôs) [key], anc. Greek Calauria, island (1991 pop. 3,570), c.8 sq mi (20 sq km), SE Greece, in the Aegean Sea near the Argolis peninsula of the Peloponnesus. It is famous for its fine marble. There are remains of a temple of Poseidon where Demosthenes took poison and died in 322 B.C. Representatives of Britain, France, and Russia met on Póros in 1828 to discuss the future of the new Greek state.