Columbia subject headings:
City walls--Italy.
Harvard subject headings:
Architecture--Europe--History
Cities and towns, Medieval.
Cities and towns--Europe--History
Cities and towns--History
City walls--Europe--History.
City walls--History.
Fortification--Europe--History.
Princeton subject headings:
Architecture--Europe--History.
Cities and towns, Medieval--Europe--History.
Cities and towns, Renaissance--Europe--History.
City walls--Europe--History.
Fortification--Europe--History.