PERINTHUS (Turk. Eski Eregli, old Heraclea), an ancient town of Thrace, on the Propontis, 22 m. W. of Selymbria, strongly situated on a small peninsula on the bay of that name. It is said to have been a Samian colony, founded about 599 B.C. According to Tzetzes, its original name was Mygdonia; later it was called Heraclea (Heraclea Thraciae, Heraclea Perinthus). It is famous chiefly for its stubborn and successful resistance to Philip II of Macedon in 340; at that time it seems to have been more important than Byzantium itself.