Pá·trai (pä'trě) A city of southern Greece in the northwest Peloponnesus on the Gulf of Pátrai, or Gulf of Patras, an inlet of the Ionian Sea. The city was an important trade center by the fifth century B.C. but declined before the Roman conquest of Greece (146 B.C.). Its commercial importance revived during the Middle Ages. Population: 161,000.