Research objectives: To analyse information of the sources of the 13th–16th centuries regarding the “Bascardi”, “Pascatur”, “Baschirdi”, “Bashkirds”, “Bashkirs” (together with other variations) and to study the interrelation of these ethnonyms and the historical fate of those who bore them. Research materials: In addition to written sources (Latin, Russian and Arabic), materials from archaeological research, linguistic data, epigraphy, historical ethnology and climatology. Research results and novelty: Prior to the Mongol-Tatar invasion, “Magna Hungaria”, located east of Bolghar, was inhabited by the “Bascardi” who, according to written sources and archaeology, belonged to the nomadic Ugrians and consisted mostly of pagans. During the Great western campaign of the Mongols, most of the Cisuralic Ugrians (“Bascardi”) perished or left this territory (one part of the population fled from the invaders and the other one was deported). During the Golden Horde period, Muslim Turks from the Bolghar and Central Asia settled in the Cisuralic region and gradually assimilated the remains of the “Bascardi” of the Southern Cis-Urals. In the 15th–16th centuries, the ethnonyms “Baschirdi”, “Bashkirs” and the like are not associated with the Southern Cis-Urals, but with more northern territories – that is, with the upper reaches of the Kama. Due to serious climatic and political changes that began in the 1550s (one of the climatic minima of the Little Ice Age, the fall of the Kazan Khanate, and turbulence combined with epidemics in the Nogai Horde), the “Bashkirs” began to move to the Southern Cis-Urals, as is evidenced by the sources of the late 16th–17th centuries.