Forte Longone, or Forte Beneventano, is a fortification located in the municipality of Porto Azzurro. This name derives from the area on which it was built, formerly called Porto Longone. It was built by the Spaniards at the beginning of the seventeenth century (1603-1605) with the aim of strengthening the coastal defence system of the State of the Presidi; in the mid-nineteenth century it was converted into a prison, a function it still performs today, exploiting also its strategic position, situated on the top of the promontory of Porto Azzurro.
Inside the fortification there are buildings of various kinds, both for private use, such as the former Governor's Palace or the former armory, and for public use, such as the warehouses, the hospital and two churches: the Baroque church of San Giacomo Maggiore and the chapel of Santa Barbara in Piazza d'Armi.
The fortification has a star-shaped plan, which can be traced back to an irregular pentagonal polygon and it has a wall bounded by ditches to increase the protection of the building.