Columbia subject headings:
Bulgaria--History--1018-1185.
Byzantine Empire--History--1081-1453.
Byzantine Empire--History--527-1081.
Harvard subject headings:
Bulgaria--History
Bulgaria--History--1018-1185
Byzantine Empire--History
Byzantine Empire--History--1081-1453
Byzantine Empire--History--527-1081
Princeton subject headings:
Bulgaria--History--1018-1185.
Byzantine Empire--History--1081-1453.
Byzantine Empire--History--527-1081.