Syr Darya (also known as Syrdarya or Sirdaryo) is a river in Central Asia. It rises in two headstreams in the Tien Shan mountains in Kyrgyzstan and eastern Uzbekistan and flows for some 2,220 km (1,380 miles) west and north-west through southern Kazakhstan to the Aral Sea.
The name is a relatively recent one in western writings; prior to the early 20th century, the river was known as the Jaxartes.
This river marked the northernmost limit of Alexander the Great's conquests; here in 329 he founded the city Alexander Eschatê as a permanent garrison.
See also Amu Darya.