Columbia subject headings:
Castles--Italy--Marche.
Fortification--Italy--Marche.
Harvard subject headings:
Castles--Italy--Marche--History.
Fortification--Italy--Marche--History.
Marche (Italy)--History, Military.
Princeton subject headings:
Castles--Italy--Marche.
Fortification--Italy--Marche--History.
Marche (Italy)--History, Military.