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 by its ancient Greek name, the Jaxartes.
This river marked the northernmost limit of Alexander the Great's conquests; here in 329 BCE he founded the city Alexander Eschatê (literally, "Alexandria the Furthest") as a permanent garrison. The city is now known as Khujand.
He had already decided to accept the riverJaxartes as the northeastern frontier of his empire, as it had been during the days of the Achaemenid Empire that he had overthrown.
The Jaxartes is wider than a bowshot, which meant that the Macedonians could board their hurriedly prepared ships and rafts in safety, but that they would enter the Sacan field of fire halfway across the river.
Alexander's archers were the first to disembark, positioning themselves as a covering screen for the rest of the force; the cavalry followed, and the soldiers of the phalanx were the last ones to arrive.