The Aragonese layout was designed by Ciro Ciri with the help of Francesco di Giorgio Martini and built by Ferdinando I of Aragon between 1485 and 1498 enclosing the Swabian fortifications and the improvements introduced by the Turks who had occupied the City for over a year (1480).
It is surrounded by a dry moat and has a pentagonal and irregular layout, three cylindrical towers on the corners and on the seaward side, a tapered rampart with external balwards added in 1578; on the ramparts there are the coats of arms of Antonio De Mendoza and Don Pedro da Toledo.
On the entrance portal the large coat of arms of Charles V can be found.