Columbia subject headings:
Castles--Conservation and restoration--Europe--Congresses.
Castles--Europe--History--Congresses.
Fortification--Europe--History--Congresses.
Lost architecture--Europe--History--Congresses.
Harvard subject headings:
Castles--Conservation and restoration--Europe--Congresses.
Castles--Europe--History--Congresses.
Fortification--Europe--History--Congresses.
Lost architecture--Europe--History--Congresses.
Princeton subject headings: