Columbia subject headings:
Aachen Region (Germany)--Buildings, structures, etc.
Aachen Region (Germany)--History.
Castles--Germany--Aachen Region.
Palaces--Germany--Aachen Region.
Harvard subject headings:
Aachen Region (Germany)--History.
Castles--Germany--Aachen Region.
Palaces--Germany--Aachen Region.
Princeton subject headings:
Aachen Region (Germany)--History.
Castles--Germany (West)--Aachen Region.
Palaces--Germany (West)--Aachen Region.