The Cassero Senese, was built in one year from 1344 to 1345, by the will of the Sienese Republic to defend the city from both external attacks and internal revolts and was connected, through the curtain walls to three turreted formworks. At the time of construction the complex was to have an imposing appearance in the surrounding marshy countryside with a watchtower and a courtyard with a door and an anti-port, but with the Medici intervention the structure was deeply modified. Grosseto became the prototype fortified city with a mighty city wall and the Cassero inserted in the main bastion, remained several meters underground with respect to the new floor of the bastioned ring, the courtyard between the two Sienese doors was turned to barrel and all the complex took on the appearance of a squat and imposing building. In the central part of the new Medicean Fortress, a real military citadel destined to house a garrison, as well as to function as guards and defense, the barracks, a hospital, the warehouses for storing foodstuffs arose next to the military governor's headquarters. the chapel of Santa Barbara and in the center of this large rectangular space called Piazza d'Armi, an octagonal well was built which took the water from the enormous cistern below. Behind the Piazza d'Armi, two open-air guns contained war machines. From these posts, through a tunnel, one descended to the low squares, equipped with a deposit for the powders where the riflemen were found, who, through the loopholes, fired at the enemy.