river, the major headstream of the Euphrates. In antiquity it was called Arsanias. The river rises north of Lake Van near Mount Ararat, in eastern Turkey, and flows westward for 449 miles (722 km) through a mountainous region to unite with the Karasu Çayı and form the Upper Euphrates near Malatya. Turkey's largest dam, the Keban, west of Elâzığ, completed in 1974, is designed to provide electric power and aid flood control and the irrigation of additional cropland. Agriculture in the valley consists primarily of the cultivation of grains, fruits, vegetables, and cotton.