Columbia subject headings:
Bulgaria--Civilization--Congresses.
Bulgaria--History--681-1018--Congresses.
Bulgaria--Relations--Byzantine Empire--Congresses.
Byzantine Empire--Relations--Bulgaria--Congresses.
Samuil, Czar of Bulgaria, -1014--Congresses.
Harvard subject headings:
Bulgaria--Civilization.
Bulgaria--History--681-1018.
Bulgaria--Relations--Byzantine Empire.
Byzantine Empire--Relations--Bulgaria.
Samuil, Czar of Bulgaria, -1014.
Princeton subject headings: