Columbia subject headings:
Castles--France--History.
Castles--Great Britain--History.
Castles--Middle East--History.
Crusades.
Fortification--France--History.
Fortification--Great Britain--History.
Fortification--Middle East--History.
Harvard subject headings:
Castles--France
Castles--France--History.
Castles--Great Britain
Castles--Great Britain--History.
Castles--Middle East--History.
Castles--Middle East.
Crusades.
Fortification--France--History.
Fortification--Great Britain--History.
Fortification--Middle East--History.
Military architecture--France--History.
Military architecture--Great Britain--History.
Military architecture--Middle East--History.
Princeton subject headings:
Castles--France--History.
Castles--Great Britain--History.
Castles--Middle East--History.
Crusades.
Fortification--France--History.
Fortification--Great Britain--History.
Fortification--Middle East--History.