Columbia subject headings:
Harvard subject headings:
Architecture, Medieval--Italy--Sicily.
Castles--Italy--Sicily.
Frederick II, Holy Roman Emperor, 1194-1250--Homes and haunts--Italy--Sicily.
Military architecture--Italy--Sicily.
Sicily (Italy)--Description and travel
Princeton subject headings:
Castles--Italy--Sicily--History.
Frederick II, Holy Roman Emperor, 1194-1250--Homes and haunts--Italy--Sicily.
Sicily (Italy)--History--1194-1282.