Information Bulgaria: A Short Encyclopaedia of the People's Republic of Bulgaria, Pergamon Press, (ISBN9780080318530, lire en ligne)
András Róna-Tas, Hungarians and Europe in the Early Middle Ages: An Introduction to Early Hungarian History, Central European University Press, , 242, 264, 377 (ISBN9789639116481, lire en ligne)
Roumen Daskalov, Master Narratives of the Middle Ages in Bulgaria, BRILL, , 74, 119–120 (ISBN9789004464872, lire en ligne)
Ján Steinhübel, The Nitrian Principality: The Beginnings of Medieval Slovakia, Brill, , 99, 106 (ISBN9789004438637, lire en ligne)
Dennis P. Hupchick, The Bulgarian-Byzantine Wars for Early Medieval Balkan Hegemony: Silver-Lined Skulls and Blinded Armies, Springer, , 124–125 p. (ISBN9783319562063, lire en ligne)
Komatina, « The Slavs of the mid-Danube basin and the Bulgarian expansion in the first half of the 9th century », Зборник радова Византолошког института, vol. 47, , p. 4 (lire en ligne)