The town of Capalbio has an old defensive circle of walls, formed by a original, medieval belt that dates back to the period between the 11th and 12 centuries. It was commissioned by the Aldobrandeschi for the purposes of defence and a vantage point over the surroundings of the Capalbio Fortress, a centre of feudal power.
The walls were modified in the 15th century under the Republic of Siena, who built a second ring inside the first. The interior, Renaissance walls are lower than the older ones, and between the two there is a series of watchtowers, most of them built to a square plan. The bottom of the walls are sloped on the outside, and some of the battlements merge into the outside walls of town buildings.
Because of the different height of the two walls the double walkway is particularly unusual, having been built at different levels, but it offers a superb panoramic view. The walls have two gates set at opposite sides of the defensive circle, the main one being Porta Senese, which bears not only a plaque from 1418 to commemorate the restructuring of the walls, but also the Medici coat-of-arms from 1601, when Capalbio was annexed by the Grand Duchy of Tuscany.