Poros is a small Greek island-pair in the southern part of the Saronic Gulf, at a distance about 58 km (36 mi) (31 nautical miles) south from Piraeus and separated from the Peloponnese by a 200 m (656 ft) wide sea channel, with the town of Galatas on the mainland across the strait. Its surface is about 31 square kilometres (12 sq mi) and it has 3,780 inhabitants. The ancient name of Poros was Pogon. Like other ports in the Saronic, it is a popular weekend destination for Athenian travellers.
Poros consists of two islands: Sphairia the southern part, which is of volcanic origin, where today's city is located, and Kalaureia also Kalavria or Calauria (meaning 'gentle breeze'), the northern and largest part. A bridge connects the two islands over a narrow isthmus.