Columbia subject headings:
Harvard subject headings:
Bulgaria--History--To 1393--Congresses.
Simeon I, King of Bulgaria, 864 or 865-927--Congresses.
Princeton subject headings:
Akheloĭ (Bulgaria)--History.
Balkan Peninsula--History.
Bulgaria--History--681-1018.
Simeon I, King of Bulgaria, 864 or 865-927.