Columbia subject headings:
Bulgaria--Military relations--Byzantine Empire--Sources.
Byzantine Empire--History--Sources.
Byzantine Empire--Military relations--Bulgaria--Sources.
Crimea (Ukraine)--History--Sources.
Danube River Valley--History--Sources.
Gotskiĭ Toparkh.
Kievan Rus--History--862-1237--Sources.
Harvard subject headings:
Bulgaria--History--To 1393.
Byzantine Empire--History.
Princeton subject headings:
Bulgaria--Military relations--Byzantine Empire--Sources.
Byzantine Empire--History--Sources.
Byzantine Empire--Military relations--Bulgaria--Sources.
Crimea (Ukraine)--History--Sources.
Danube River Valley--History--Sources.
Gotskiĭ Toparkh.
Russia--History--To 1533--Sources.