Columbia subject headings:
Castles--Italy--Fermo--History.
Fermo (Italy)--History--To 1500.
Fortification--Italy--Fermo--History.
Lost architecture--Italy--Fermo.
Harvard subject headings:
Castles--Italy--Fermo.
Coast defenses--Italy--Fermo.
Excavations (Archaeology)--Italy--Fermo.
Fermo (Italy)--Antiquities.
Princeton subject headings: