Columbia subject headings:
Church history--11th century.
Church history--12th century.
Church history--13th century.
Crusades.
Harvard subject headings:
Church history--11th century.
Church history--12th century.
Church history--13th century
Crusades
Princeton subject headings:
Church history--11th century.
Church history--12th century.
Church history--13th century.
Crusades.