The northern portion of Iraq, known as Al Jazira, is mountainous. Elevations of about 2100 m (about 7000 ft) above sea level are reached near the Turkish border; in the northeastern part of the country there are peaks ranging to 3600 m (11,811 ft) atop Mount Ebrâhim. Farther south the country slopes downward to form a broad, central alluvial plain, which encompasses the valley of the Tigris and Euphrates rivers. The extreme southeastern portion of Iraq is a low-lying, marshy area adjacent to the Persian Gulf, on which Iraq fronts for a distance of about 40 km (about 25 mi). West of the Euphrates, the land rises gradually to meet the Syrian Desert.
Present-day Iraq occupies the greater part of the ancient land of Mesopotamia, the plain between the Tigris and Euphrates rivers. The two rivers flow through Iraq from northwest to southeast. They meet about 160 km (about 100 mi) north of the Persian Gulf to form the Shatt al Arab, which drains into the gulf. The chief tributaries of the Tigris are the Great Zab, the Little Zab, and the Diyala rivers. Level terrain separates the Tigris and the Euphrates in their lower courses. In ancient times the two rivers were joined by a network of canals and irrigation ditches, which directed the water of the higher-lying and more westerly Euphrates across the valley into the Tigris.
