The Kazakh territory was a key constituent of the Eurasian trading Steppe Route, the ancestor of the terrestrial Silk Roads. Archaeologists believe that humans first domesticated the horse (i.e., ponies) in the region's vast steppes. During recent prehistoric times, Central Asia was inhabited by groups such as the possibly Proto-Indo-European Afanasievo culture, later early Indo-Iranians cultures such as Andronovo, and later Indo-Iranians such as the Saka and Massagetae. Other groups included the nomadic Scythians and the Persian Achaemenid Empire in the southern territory of the modern country. In 329 BC, Alexander the Great and his Macedonian army fought in the Battle of Jaxartes against the Scythians along the Jaxartes River, now known as the Syr Darya along the southern border of modern Kazakhstan.