Columbia subject headings:
Bulgaria--Antiquities.
Bulgaria--History, Military.
Excavations (Archaeology)--Bulgaria--Kaliakra, Cape.
Fortification--Bulgaria--Kaliakra, Cape.
Kaliakra, Cape (Bulgaria)--Antiquities.
Harvard subject headings:
Bulgaria--Antiquities.
Kaliakra (Bulgaria)--Antiquities.
Princeton subject headings:
Kaliakra, Cape (Bulgaria)--Antiquities.