The Rocca aldobrandesca of Porto Ercole, more commonly known as Rocca Spagnola, is a coastal fortification located in the homonymous village of Monte Argentario; in the past centuries it was one of the bulwarks of the defensive system of the promontory.
On the hill where currently stands La Rocca there was in ancient times a small oratory dedicated to St. John the Evangelist, mentioned by Pope Gregory VII in a papal bull of 1074. Unfortunately, the medieval history of this territory has reached us very confused, since these lands were conquered and sold after a few years. There was stability only when this territory was given in emphyteusis to Margherita Aldobrandeschi, Countess of Sovana, from the Abbey of the Three Fountains. She had a square tower built on the current hillock of the Fortress as a symbol of power stone. This tower will constitute the first nucleus of the Rocca. Later the tower was inherited by the Orsini of Pitigliano, who completed the work of fortification. With the conquest of Porto Ercole by the Sienese in the fifteenth century and the subsequent annexation to the Republic of Siena, the famous artist Lorenzo di Pietro called il Vecchietta was sent to Porto Ercole to restore and expand the castle. He added two circular towers, giving the castle a triangular shape. However, there was a need to build a village at the foot of the fortification, so the Vecchietta was ordered to build an “habitable land, at least as large as the field of the city of Siena”. The architect then built a curtain wall that descended from the two circular towers to the sea, giving it two doors, the main one with a sharp Sienese arch and protected by bertesca, and the secondary with a lowered arch and controlled by a semi-cylindrical tower. He also rearranged a Byzantine tower that was at the entrance of the port, using it as a meeting point for the curtain walls. At this moment Porto Ercole appeared as a large castle walled and turreted, crowned at the top by a triangular fortress. In 1487, the military engineer Francesco di Giorgio Martini carried out works aimed at extending and reinforcing the construction of the Vecchietta. He put his hand more to the Rocca, giving it more walls, and of two triangular formwork, the village itself. In addition, the Byzantine tower was replaced by incorporating it into a large defensive rampart, the Bastion of Santa Barbara, which was accessible from the Rocca by a covered walkway within the walls. But the problem of the Rocca remained the water supply, given the lack of nearby springs. They were then built in the fortification of the vaulted cisterns, with a surface of wells, for the collection of rainwater.
Still under Sienese domination, during the Renaissance period, other redevelopment works were carried out in 1543 on a project by Anton Maria Lari, which was inspired by the canons of Baldassarre Peruzzi: in this phase the boundary walls were strengthened. Later the works were directed by Bernardo Buontalenti, who greatly expanded the fortress, providing it with imposing bastions and embankments, thus transforming it into a modern fortification. In addition he should be remembered for the construction of the chapel of San Giovanni, a small jewel of the Renaissance, using the previous medieval oratory as a sacristy. These widgets gave the current form to the fortification. In this long period the fortress constituted a point of reference for the defense system of the southern coast of the Republic of Siena, carrying out sighting, defense and offense functions, as well as being able to communicate through luminous signals with the Sant’Ippolito Fort to the west, which stood in the place of Forte Stella, and with the Fort of Galera to the north, which stood where Fort Filippo was later built.
In the second half of the sixteenth century, the entire area of the Argentario became part of the State of the Presidios and the fortification was integrated into the defensive system of the promontory, within which it carried out functions of sighting, defense and offense. During this period the Spaniards commissioned the military engineer Giovanni Camerini as director of the renovation of the pre-existing defensive structure, which was further fortified with the strengthening of the external bastion fortified and the sentry boxes; underground tunnels were also built through which the defensive structure was connected to the Palace of the Rulers.
In the nineteenth century the fortress temporarily became a defensive outpost of the Grand Duchy of Tuscany, and then finally passed to the Kingdom of Italy. Just after the unification of Italy began the gradual dismantling of the military structure, while in 1862 was built the lighthouse of Porto Ercole, circular plan, at the corner of the fortress next to the tip