The last plundering at the hands of Gian Galeazzo Visconti in 1397 convinced the Republic of Florence to take action by fortifying the hamlets of Lastra – located in a strategic position, where several trade routes intersected – and of Malmantile. Filippo Brunelleschi was also involved in the project, finished in 1426.
The perimeter of the walls of Lastra is the shape of an irregular square and built on nearly flat land. The defensive walls enclose roughly 4 hectares crossed by two roads: the ancient Via Pisana, from east to west, which connects the city gates Porta Fiorentina and Porta Pisana, and a north-south road that leads to the ancient city gate called Portone di Baccio.
The exterior of the walls is quite irregular and is made of various materials. The perimeter was once marked by ten towers, only seven of which have survived.
Within the walls there are still a few sites worthy of notice, such as the church of the Misericordia (Mercy), the Spedale di Sant’ Antonio, the tabernacle of the Podestà (Chief Magistrate) and the Palazzo del Podestà.