Columbia subject headings:
Architecture, Medieval--Italy--History.
Castles--Italy--History.
Frederick II, Holy Roman Emperor, 1194-1250--Homes and haunts--Italy.
Harvard subject headings:
Architecture, Medieval--Italy--History.
Castles--Italy--History.
Frederick II, Holy Roman Emperor, 1194-1250--Homes and haunts--Italy.
Princeton subject headings:
Architecture, Medieval--Italy.
Castles--Italy--History.
Frederick II, Holy Roman Emperor, 1194-1250--Homes and haunts--Italy.