Both the Euphrates and the Tigris rise in the mountains of southeastern Turkey and flow across the progressively drier central lowlands of Syria and Iraq to join to form the Shatt al-Arab at Basra, just above the head of the Persian Gulf. The Tigris receives flow from a series of rivers that drain the western slopes of the Taurus-Zagros; one of these, the Kharun, enters the Shatt al-Arab below the junction of the Tigris.