The Bulgars were Turkic semi-nomadic warrior tribes that flourished in the Pontic–Caspian steppe and the Volga region during the 7th century. They became known as nomadic equestrians in the Volga-Ural region, but some researchers say that their ethnic roots can be traced to Central Asia. They spoke a form of Turkic as their main language. The Bulgars included the tribes of Onogurs, Utigurs and Kutrigurs, among others. The first clear mention of the Bulgars in written sources dates from 480, when they served as the allies of the Byzantine Emperor Zeno. In the first half of the 6th century, the Bulgars occasionally raided the Byzantine Empire.