Forte di Belvedere

The Forte Belvedere or Fortezza di Santa Maria in San Giorgio del Belvedere (often called simply Belvedere) is a fortification in Florence, Italy. It was built by Grand Duke Ferdinando I de' Medici during the period 1590–1595, with Bernardo Buontalenti as the designer, to protect the city and the Medici rule thereover. In particular, it was used to hold the Medici treasury.

More info at  en.wikipedia.org