Columbia subject headings:
Architecture, Medieval--Germany--Thuringia--Congresses.
Castles--Germany--Thuringia--Congresses.
Fortification--Germany--Thuringia--Congresses.
Harvard subject headings:
Architecture, Medieval--Thuringia--Germany--Congresses.
Castles--Thuringia--Germany--Congresses.
Fortification--Thuringia--Germany--Congresses.
Princeton subject headings: