Usually the castles have a stratification of ages and functions. Each castle is different from the other in a large variety of types and constructive solutions. The main functional characteristics are defined between the eleventh and fifteenth centuries. After they change substantially during the Renaissance, with the final impose of firearms, running out in short time their military role.In smaller fortifications everything was reduced to a bare minimum. Their origin could be an isolated watch- and signal tower. Visual connections were guaranteed by fires during the night and mirrors and smoke signals during the day.In the smaller forts everything was reduced to the essential. Their origin could be an isolated tower of sighting and reporting. Visual connections were guaranteed by fires during the night and smoke and mirrors during the day.The primitive forms of the castle were small natural or artificial heights of truncated cone surmounted by a high wooden tower. The whole was surrounded by a palisade, a walkway and a moat. Common in France and England they were brought in southern Italy by the Normans. To this system a second external enclosure was added, connected to the first by a movable bridge, within which chambers, stables, storerooms and service rooms were arranged. The wooden structures were soon replaced by the stone or brick masonry, more resistant in case of fire. The tower later developed in two different variants: the first consists of a large stone slab, said “the dungeon”, the second of a large cylinder, which allowed to obtain a better shooting sector, without dead corners. With the appearance of the first artillery the towers could be arranged protruding at an angle from the wall toward the attacker, with a form like the bow of the ship or with pentagonal plant (the so-called struts). The dungeon, with the first floor entrance, it evolved into the keep – the main tower – which also housed the accommodation or the feudal lord or of the castle commander.