Columbia subject headings:
Europe, Central--Foreign relations--Holy Roman Empire.
Frederick I, Holy Roman Emperor, approximately 1123-1190.
Holy Roman Empire--Foreign relations--Europe, Central.
Harvard subject headings:
Europe, Central--Foreign relations--Holy Roman Empire.
Frederick I, Holy Roman Emperor, approximately 1123-1190
Holy Roman Empire--Foreign relations--Europe, Central.
Princeton subject headings:
Europe, Central--Foreign relations--Holy Roman Empire.
Frederick I, Holy Roman Emperor, approximately 1123-1190.
Holy Roman Empire--Foreign relations--Europe, Central.