Columbia subject headings:
Castles--Europe--History.
Castles--Japan--History.
Fortification--Europe--History.
Fortification--Japan--History.
Harvard subject headings:
Castles--Europe--History.
Castles--Japan--History
Fortification--Europe--History.
Fortification--Japan--History.
Princeton subject headings:
Castles--Europe--History.
Castles--Japan--History.
Fortification--Europe--History.
Fortification--Japan--History.