The walls of Porto Ercole constitute the defensive system of the homonymous village located in the south-eastern part of the Argentario promontory.
The defensive system of the village of Porto Ercole began to develop in medieval times during the domination of the Aldobrandeschi, parallel to that of sighting along the corresponding coastal stretch.
The first tower of the defense system was built at the behest of Margherita Aldobrandeschi, Countess of Sovana, on the hill where now stands the Fortress. The tower was then inherited by the Orsini of Pitigliano, who undertook renovations. But it was the Republic of Siena to build the walls that today surrounds the village. In fact, halfway through the fifteenth century, Siena managed to tear Porto Ercole to the Orsini, who sold it to various people in exchange for building fortifications. But when Siena saw that the tenants had not built anything, he regained control of the port with the help of mayor, and sent the artist Lorenzo di Pietro called il Vecchietta with the order to build “an inhabitable land, at least as large as el Campo di Siena “. He brought down two walls from the Aldobrandesca tower, equipping them with semi-circular towers at the sides and at the top. Access to the castle was ensured by two doors, the main one being at the bottom and decorated by a Sienese Gothic arch and controlled at the top by a bertesca. Instead the secondary access was half-walled and controlled by a tower. At the time the towers were seven plus the bertesca: Mastra tower (Aldobrandesca), North tower (Mastio Senese), Torre del Fieno, Torre di Mezzo Est, Torre di Mezzo Ovest, Torre di Mare, Torre del Molo. The towers were connected by a walkway protected by Guelph battlement. The complex appeared in the Late Gothic style, with high and slender walls, sharp arches, merlons, tall and slender towers. Later the castle was restored by the military engineer Francesco di Giorgio Martini, who built the Bastion of Santa Barbara at sea, readjusting a previous Byzantine lighthouse, joined with a wall the north tower and the tower of the Hay making a triangular formwork, which he connected by means of a secret passage inside the walls to the bastion of Santa Barbara. It also equipped the Sienese keep (the Rocca) with a new city wall. Instead it dates back to the 16th century the octagonal tower built over the bertesca of the Sienese gate, which constituted the clock tower.
The walls completely delimit the historic core of Porto Ercole.
The defensive system, as a whole, is dominated by the aldobrandesca fortress, an imposing fortified complex situated at the top of the promontory that dominates the village below.
From the two sides of the fortress, two different sections of curtain walls descend, which completely close the historical part of the town; the north-eastern wall, which in a long stretch culminates with a summit crenellation, reaching the floor incorporates the characteristic access door with a Sienese arch in international Gothic style dominated by the clock tower, equipped with a bell.
On the western side, the curtain wall closes the scenic Piazza di Santa Barbara, where the Governors’ palace faces; the square is situated in a panoramic position near the Bastion of Santa Barbara, joined to the overhanging Aldobrandesque fortress through a series of underground passages and secret passageways.