Stepanov, T., & Stefanova, T. (2010). The Bulgars and the Steppe Empire in the Early Middle Ages: The problem of the others. Brill.

Stepanov, T͡Svetelin, and Tati͡ana Stefanova. The Bulgars and the Steppe Empire in the Early Middle Ages: The Problem of the Others. Leiden [The Netherlands] ; Boston: Brill, 2010.

Stepanov, T͡Svetelin, and Tati͡ana Stefanova. The Bulgars and the Steppe Empire in the Early Middle Ages: The Problem of the Others. Brill, 2010.