Pi·rae·us (pī-rē'əs, pĭ-rā'-) A city of east-central Greece on the Saronic Gulf southwest of Athens. Its port was built in the 5th century B.C. and after extensive development in the mid-19th century became the principal seaport of the country. In ancient times it was connected with Athens by the Long Walls, two parallel walls some 183 m (600 ft) apart. Population: 175,000.