Barsils / Barsilts, Chinese Baysi (Karachay-Balkar: Bars El - "People of Bars", barsilli, pl. barsille), were a semi-nomadic Eurasian tribe of Turkic linguistic affiliation. Barsils in turn evolved into modern Karachays and Balkars, and possibly identical with the Bagrasik. Barsils are first mentioned in the Chinese annals as the 15th of the 15 Turkic Tele tribes. The Chinese records about the Western Turkic Kaganate c. 630 mention a Khan of the Bars (Tr. leopard) tribe, a member of five "Nushibi" (Ch. ) on-shadapyt right wing tribes, under a name of Tun-ashpa [ra]-erkin. Barsils are included in the list of steppe people living north of Derbend in the Late Antique Syrian compilation of Zacharias Rhetor, and are also mentioned in documents from the second half of the 6th century in connection with the westward migration of the Eurasian Avars. When the Avars arrived, according to Theophylact Simocatta, "the Barsilt (Barsilians), Onogurs, and Sabirs were struck with horror (...) and honoured the newcomers with brilliant gifts."
In an Armenian geography of the 7th century, the Barsils are described as living on an island, distinct from the Bulgars and Khazars and at odds with both nations. In addition, it describes them as possessing large flocks of sheep, supporting the notion that they were at least partly nomadic. Mikhail Artamonov theorized that "Barsilia" was located in northern Daghestan, but subsequent scholars have disputed this theory, as the sedentary local population of the relevant period and region appears to have been, for the most part, settled in permanent fortress-towns.
Some archeologists believe that the Barsils lived near the Volga delta, which would explain the Armenian reference to them as island-dwellers. This is supported by Theophanes' statement that the "populous people of the Khazars came out from the innermost parts of Bersilia in Sarmatia Prima." If indeed they lived on the lower Volga, they were almost certainly conquered by the Khazars, whose capital Atil was in the same region from the mid-8th century on.
Eventually at least part of the Barsil nation is believed to have settled in Volga Bulgaria. In the 10th century, ibn Rustah reported that the three nations of Volga Bulgaria were "Bersula", "Esegel", and "Bulgar". Thereafter the Barsils were likely assimilated by the Volga Bulgars.