On 16 July 1406 a Florentine army captured Vicopisano, the last stronghold of the Republic of Pisa, after nine months’ hard siege. A new fortress needed to be constructed, a fortress which had to be impregnable. Florence commissioned Filippo Brunelleschi to produce a design. Construction began in 1435. Many of the churches and palaces of Vicopisano were torn down. The new fortification incorporated a 12th-century tower which had been the property of the archbishops of Pisa.
The tower became the keep of the new fortress, retaining medieval features such as the high walls. A surprising novelty was the series of drawbridges designed to isolate the different parts of the fortress, forming a number of concentric rings separable from one another in case of enemy attack.
For example, before gaining access to the courtyard the enemy needed to conquer the gatehouse, which was protected by a drawbridge and a moat. If the courtyard was about to be lost, defenders had the opportunity to pull down the stairs resting on four thin arches and connecting the courtyard to the parapet walk on top of the curtains. If the enemy had managed to climb up to the curtains, the defenders would have retreated to the tower. The tower could be isolated from the rest of the fortification by pulling up the drawbridge that connected the parapet walk to the only access to the tower.
The tower was equipped with a cistern and a provisions store to allow its occupants to withstand a long siege. But the most ingenious solution is the mighty wall which descends from the fortress to the foot of the hill, ending in a tower rising to a height of about 21 metres. Had the enemy managed to get into Vicopisano, it would have been impossible for them to besiege the fortress and cut off food supplies to starve the town into submission.