Columbia subject headings:
Byzantine Empire--Church history.
Church history--Middle Ages, 600-1500.
Church history--Primitive and early church, ca. 30-600.
Crusades.
Eastern churches--History.
Orthodox Eastern Church--History.
Harvard subject headings:
Byzantine Empire--Church history.
Church history--Middle Ages, 600-1500
Church history--Primitive and early church, ca. 30-600
Crusades.
Orthodox Eastern Church--History.
Princeton subject headings:
Byzantine Empire--Church history.
Church history--Middle Ages, 600-1500.
Church history--Primitive and early church, ca. 30-600.
Crusades.
Orthodox Eastern Church--History.