The Corso Rome and the Corso Diomede, parallel to each other, are dominated by the castle and fortress that can be reached through a short and wide road on staircases. The Castle, built around the fifteenth century, and later to defend the monastery, included "L'habitatione de' Canonici, e da alcuni Officiali, artisti e manuali: come sono i medici, barbieri, spetiali, sartori, calzolai, panettieri, vignaiuoli, legnaioli, muratori ed altri serventi in diverse cose ed i passeggeri; il Capitano co' soldati habitano fuori giorno e notte."
The fortress, colossal work really is the last bastion of defense of the castle of Badia. A high and long wall with battlements, close the neck of the head of the defensive from north to south side on which the castle next door had 3. To the right front of this wall of the fortress, topped by the cross emblem, flanked and protected from solid Torre del Ponte, the surplus ancient fortress built by Charles II D'Angio, crowned top by piombatoi, opens before they fitted a time the drawbridge on the deep ditch was dug for the entire length of the wall, about 10 meters wide, of which vestiges of the outside wall is known to the left side of the square below said "Against Pit", today used as a sports field. The height of the wall, and the Tower Bridge from the bottom of the ditch was considerable and therefore the castle could also consider impregnable by the assailants numerous and well-armed. On the walls of the front wall you notice loopholes for carabiners, culverins for windows, while the upper stretch the sidelines, grand terraces on open boundless horizons. On the left are the ruins of the towers Knight called the hospital and left portal rises a majestic square tower. Varcato the first portal Castle opens the entrance to the Tower Angioino that was another guard. The stradella in stairwells, called "Ascent of the Church", is flanked on the right by Wall ending on the walls of high square tower, turning left through a small ramp, we arrive on the Forts Torrione Angioino with piombatoi where the brothers poured oil on the attackers, boiling water, lead time and other gimmicks on defence. Here you can admire the view of the village sheds aligned with the Corsican Diomede, facing Roma and Corsican more left with basically the island of San Domino and the right Cretaccio. To complete the defence of the castle to the east is building the Tower of Knights of St. Nicholas under which there is a great "Cut" in vivo stone, very deep, which was done to arrive in depth until you communicate to divide the sea from the castle rock of St. Nicholas and make sure that they remain isolated from all sides not offering more side of an attack by land, more difficult to contain the few men of the defence.