Poros, the ancient Kalureia, lies south-west of the Methana Peninsula, separated from the north coast of the Argolid by a strait between 250 m and 1000 m wide, 1.5 km long and up to 4 meters deep. Most of the island is covered with thin woodland. The inhabitants, many of whom are of Albanian descent, live by farming the fertile coastal areas on the mainland which belong to Poros and by the tourist trade. There was a settlement in Mycenaean times on the site later occupied by the Sanctuary of Poseidon. The ancient city was abandoned after the Roman period, and the modern town was established only in the late Middle Ages.
The island’s capital, Poros (pop. 4300; naval training school), is beautifully situated on ancient Sphairia, a headland of volcanic origin on the south side of the island linked with it by the narrow Bisti Isthmus. In the 18th and 19th century this was the principal naval harbour on the south-east coast of Greece. 5 km north-east of the town are scanty remains of the Sanctuary of Poseidon (5th century BC), the centre of the Kalaurian amphictyony (religious league) of the maritime cities on the Saronic and Argolic gulfs. It was here that Demosthenes, fleeing from the henchmen of the Macedonian Governor Antipatros, poisoned himself in 322 BC. The numerous remains of buildings in the surrounding area suggest that this was the site of ancient Kalaureia. 4 km east of Poros is the 18th century Monastery of Zoodokhos Piyi.
On the mainland opposite the island lies the huge lemon grove of Lemonodasos (30,000 trees), which belongs to Poros. 10 km west, at the village of Damalas, are the scanty remains of ancient Troizen, the setting of the legend of Hyppolytos and Phaidra.