Vizantiĭski i bŭlgarski kreposti V-X vek - Ovcharov, Dimitŭr (Izd-vo na Bŭlgarskata akademii͡a na naukite, 1982)
Titles on added t.p.: Vizantiĭskie i bolgarskie kreposti V-X volume ; Forteresses byzantines et bulgares Ve-Xe s.