Columbia subject headings:
Harvard subject headings:
Architecture, Medieval--Italy--Sicily--History.
Castles--Italy--Sicily--History--To 1500.
Castles--Italy--Sicily--History.
Fortification--Italy--Sicily--History.
Frederick II, Holy Roman Emperor, 1194-1250--Homes and haunts--Italy--Sicily.
Sicily (Italy)--Antiquities
Sicily (Italy)--History--1194-1282
Princeton subject headings:
Architecture, Medieval--Italy--Sicily.
Castles--Italy--Sicily.
Fortification--Italy--Sicily.
Frederick II, Holy Roman Emperor, 1194-1250.