The high tower is the oldest part of the complex and dates back to 1212, when Piombino was a free commune, the only surviving evidence of that period. It is where the city's land gate opened, which was rebuilt in the 15th century. The tower, also called the Tower of Sant'Antonio or Porta Inferi, was probably equipped with one or more bells in the highest part, under the arch, to be used on special occasions or in times of danger.
At the beginning of the 15th century, the forecourt and a front door were added, on which there is still a plaque dated 1417.
The ravelin was placed around the tower to protect it from artillery, but the date of construction is uncertain. Although the plaque that attributes its construction to Rinaldo Orsini indicates the year 1447, numerous construction elements, including the access door in lateral position, the proportions of the shoe and the muzzles, lead us to a dating between 1470 and 1504. The same tufa quarry material from the quarries of Populonia was used, which had also been used to build the Etruscan works in the area. The Rivellino has a semicircular shape and dates back to the reign of Rinaldo Orsini, husband of Caterina Appiani, when the siege of Alfonso V of Aragon was successfully thwarted. It must once have been surrounded by a moat and equipped with a drawbridge.