Columbia subject headings:
Aachen (Germany)--Antiquities.
Aachen (Germany)--Buildings, structures, etc.
Architecture, Carolingian--Germany--Aachen.
Harvard subject headings:
Aachen (Germany)--Antiquities.
Aachen (Germany)--Buildings, structures, etc.
Architecture, Carolingian--Germany--Aachen.
Princeton subject headings:
Aachen (Germany)--Antiquities.
Aachen (Germany)--Buildings, structures, etc.
Architecture, Carolingian--Germany--Aachen.