Columbia subject headings:
Fortification--Italy--History.
Fortification--Italy--Poggibonsi--History.
Harvard subject headings:
Fortezza (Poggibonsi, Italy)
Poggibonsi (Italy)--Buildings, structures, etc.
Princeton subject headings:
Fortezza (Poggibonsi, Italy)
Poggibonsi (Italy)--Buildings, structures, etc.