Kijas, A. (2007) “Small nomadic peoples, Berendei tribe, Chornye Klobuki (Black Hats) and Bierladnicy Tribe vs. Kievan Rus (Ruthenia)”, Balcanica Posnaniensia. Acta et studia, 14, pp. 145–156. doi: 10.14746/bp.2007.14.11.