The great pentagonal mass of the Fortress of San Giovanni is known to everyone as the Fortress "Da Basso" because it is located on the river plain.
It was built around the medieval Porta Faenza beginning in 1534 by the great architect Antonio San Gallo the younger, and commissioned by the Duke Alessandro de' Medici, who wanted to create a kind of citadel of power. Indeed, in the original designs for the fortress, there was a palace to be constructed inside for the Prince himself. However, political considerations persuaded him to remain in the Medici family residence in Via Larga. The fortress was finished in 1537 and today is used as an exhibition center.