Jaxartes, the ancient name of the Sir Darya, a river of central Asia. The Naryn, its main upper branch, rises, according to Fedchen-ko's map (Petermanrts Mittheilungen, June, 1874), in Russian Turkistan, about lat. 44° 30' N. and Ion. 76° 30' E. Taking a western course, and increased by many small streams, it enters, about 20 m. below its junction with the Jumgal, the khanate of Khokan, which it traverses in a S. W. direction. Jointly with the waters of several small rivers of S. and E. Khokan, it forms the Sir Darya a little S. of the town of Namangan. The Sir Darya continues the S. W. course, enters the recently formed Russian province bearing its name, and turns soon after abruptly to the north. Reaching about lat. 45° N. and Ion. 67° E., it assumes a W. course and falls into the sea of Aral, at the N. E. side. The Jaxartes figures in the history of Cyrus, Alexander, and other conquerors, but till a time long after the Christian era was spoken of as emptying into the Caspian.