Columbia subject headings:
Castles--England--History.
Castles--Scotland--History.
Castles--Wales--History.
Harvard subject headings:
Castles--England--History.
Castles--Scotland--History.
Castles--Wales--History.
Great Britain--History.
Princeton subject headings:
Architecture, Medieval--Great Britain.
Castles--Great Britain--History.
Great Britain--History.