From their sources and upper courses in the mountains of eastern Turkey, the rivers descend through valleys and gorges to the uplands of Syria and northern Iraq and then to the alluvial plain of central Iraq. Other tributaries join the Tigris from sources in the Zagros Mountains to the east. The rivers flow in a south-easterly direction through the central plain and combine at Al-Qurnah to form the Shatt al-Arab and discharge into the Persian Gulf.[1] The rivers and their tributaries drain an area of 879,790 km²,[2] including portions of Turkey, Syria, Iraq, Iran, and Kuwait.[3][4][5][6][7]