Columbia subject headings:
Fortification--Italy--Rome--History.
Rome (Italy)--Description and travel.
Rome (Italy)--History.
Towers--Italy--Rome.
Harvard subject headings:
Fortification--Italy--Rome--History.
Rome (Italy)--Description and travel.
Rome (Italy)--History.
Towers--Italy--Rome.
Princeton subject headings:
Fortification--Italy--Rome--History.
Rome (Italy)--Description and travel.
Rome (Italy)--History.
Towers--Italy--Rome.