Columbia subject headings:
Bridges--Italy--History.
Castello sforzesco (Vigevano, Italy)
Fortification--Italy--Vigevano.
Fortification--Italy.
Strada Coperta (Vigevano, Italy)
Vigevano (Italy)--Buildings, structures, etc.
Vigevano (Italy)--History.
Harvard subject headings:
Bridges, Medieval--Italy--Lombardy.
Fortification--Italy--Lombardy.
Fortification--Italy--Vigevano.
Military architecture--Italy--Lombardy.
Military architecture--Italy--Vigevano.
Vigevano (Italy)--Buildings, structures, etc.
Princeton subject headings:
Architecture, Medieval.
Bridges, Military--Italy--Vigevano--History.
Castles--Italy--Vigevano--History.
Fortification--Italy--Lombardy--History.
Visconti family--History.