river rising south of Erzurum in the Bingöl Dağları (mountains) of Turkey; it flows eastward, forming for approximately 275 miles (440 km) the international boundary between Armenia and Azerbaijan on the north and Turkey and Iran on the south. Below the eastern boundary of Armenia, the stream emerges into a broad valley and then crosses the Muğan Steppe. After a course of about 665 miles (1,070 km), the Aras joins the Kura (Kür) River (Kura River) in Azerbaijan 75 miles (121 km) from its mouth on the Caspian Sea. Since a flood in 1897, a separate distributary of the Aras (canalized since 1909) has emptied directly into the Caspian.

The swift-flowing, unnavigable Aras provides most of the sediment forming the Kura-Aras delta. Principal tributaries of the Aras are the Arpa Çayı (Akhuryan), which receives the waters of the Kars River and Lake Çıldır in Turkey, the Hrazdan, draining Lake Sevan (Sevan, Lake) in Armenia, and the Qareh Sū, flowing off the Sabalān Mountains in northeastern Iranian Azerbaijan. On an island in the Aras stood Artaxata, seat of the Artaxiad kings (Armenia) of Armenia from 180 BC to AD 50. Some have held that the Aras River valley was the legendary Garden of Eden (Eden, Garden of).