Built by order of Phillip III of Spain on a plan by Don Garcia of Toledo, it was part of the system to control the sea routes of the State of Presidi (founded by the Spanish in 1557). The imposing San Giacomo di Longone Fortress has a star-shaped plan and dominates one of the extremities of the gulf of Mola, opposite the stretch of sea of Porto Azzurro (originally Longone, and from 1863 to 1947, Porto Longone). The fortress is today a penitentiary and can therefore not be visited. However, a spectacular itinerary has been outfitted around a part of the fortress, enabling the visitor to appreciate its enormous bulk and, at the same time, to enjoy a stupendous view of the gulf. The defensive layout of the gulf of Mola is completed by Forte Focardo, a Spanish fortress built in the second half of the 17th century on the opposite side of the gulf, on the territory of Capolivieri.