John Evelyn describes Forte Belvedere during his visit to Florence:
The Duke has added an ample laboratory, over against which stands a fort on a hill, where they told us his treasure is kept. In this Palace the Duke ordinarily resides, living with his Swiss guards, after the frugal Italian way, and even selling what he can spare of his wines, at the cellar under his very house, wicker bottles dangling over even the chief entrance into the palace, serving for a vintner’s bush.
Forte Belvedere is the second and largest fortress to be built in Florence, Italy. It was designed and built by Bernardo Buontalenti over a five-year period, between 1590 and 1595, by order of Grand Duke Ferdinando I de’ Medici. Fortifications were significant in the 16th century and a demonstration of a city’s wealth and capabilities.
The fortress is located in the southern hills of the Arno River and on the highest hill of the Boboli Gardens (the “hill” mentioned in the diary entry of Sunday 23 October 1644 —GS) . It had long been considered one of the weakest spots in the city’s defenses, a sensation that only increased with the invention of artillery in the early modern era.
From a military point of view, the fortress is located at the most strategic point, overlooking almost the entire city and surrounding area. Due to the nature of Renaissance warfare, forts were paramount in a city’s defensive strategy. The Fort served several purposes. Most importantly it was designed to protect the centre of government in Florence and the Medici family if the city came under attack. It was also constructed to protect the Pitti Palace, Oltrarno district and south end of the city. In addition to this, the fort served as a garrison for troops for over 100 years after its completion. Galileo Galilei used Forte Belvedere for his astronomical observations and after he was sentenced to life imprisonment in 1633, he lived not far from the fort in Villa Arcetri. — Wikipedia