Issus, ancient town of Asia Minor, located north of the Syrian border, near the site of present-day İskenderun (Alexandretta), Turkey. It was a seaport, built on a narrow strip of coast between high mountains and the Gulf of İskenderun (Gulf of Alexandretta). Issus is celebrated as the site of three historic battles. In the first and most important of these, fought in 333 bc, Alexander the Great of Macedonia defeated Darius III of Persia; it was one of the series of victories by which Alexander conquered the Persian Empire. In a second battle, in ad 194, Lucius Septimius Severus defeated a rival to the Roman throne. In the third battle at Issus, in ad622, the Byzantine emperor Heraclius won a victory over the Persians.