Aras (äräsˈ) [key], Armenian, Rus., Araks, Azeri Araz, river, c.600 mi (970 km) long, rising in the Transcaucasus Mts., NE Turkey. It flows generally east, forming parts of the Turkey-Armenia, Armenia-Iran, and Azerbaijan-Iran borders, before entering Azerbaijan where it joins the Kura River at Sabirabad. Much of its upper and middle courses are rapid and tumultuous, and its waters are used for irrigation. The Aras is the chief river of Armenia and its valley contains Armenia's greatest concentration of people and industries. The Aras is the Araxes of the ancients.