What is "k'o-sa"

The K'o-sa was a Uyghur tribe mentioned by ancient Chinese texts. D.M. Dunlop believed that they were connected with the Khazars and thus postulated an Uyghur rather than Hunnish origin for that people. The K'o-sa, whose belonged to a Tujue tribe, were first mentioned under Du Huan's accounts on Tongdian and possess the areas north of Syria and the Byzantine Empire. They existed under a variant name in Suishu and formed part of the Tiele confederation whose presence was around or close to the Caspian Sea.