Columbia subject headings:
Sicily (Italy)--History--Sources.
Sicily (Italy)--Politics and government.
Harvard subject headings:
Fortification--Italy--Sicily.
Sicily (Italy)--History--Sources.
Sicily (Italy)--Politics and government--Sources.
Princeton subject headings:
Charles I, King of Naples, 1226-1285.
Fortification--Italy--Sicily.
Frederick II, Holy Roman Emperor, 1194-1250.
Sicily (Italy)--History--1194-1282--Sources.
Sicily (Italy)--Politics and government--To 1282.