Columbia subject headings:
Harvard subject headings:
Castles--Italy--Sicily--History--To 1500.
Frederick II, Holy Roman Emperor, 1194-1250.
Sicily (Italy)--Buildings, structures, etc.
Sicily (Italy)--History--1194-1282
Princeton subject headings:
Castles--Italy--Sicily--History.
Frederick II, Holy Roman Emperor, 1194-1250.
Sicily (Italy)--History--1194-1282.