Fortified villages in the Central Apennines. Origin and development of defensive structures along the boundary line with the Papal States.

The morphological characteristics of the Apennine ridges in central Italy define a territory that is difficult to penetrate, hence affecting, since the earliest times, the possibility to set up resident and delimited villages delaying the establishment of real fortified structures until the fourth century BC. The oppida and castella, mentioned in the sources of the Roman Era identifying villages with people originally from central Italy, were often placed in a strategic position and in visual contact with each other, defining a first control of the territory network that finds its complete form and evolves in a structured and easily recognizable system around the tenth-eleventh century. After the fall of the Roman Empire there was found a solution for the difficult identification of the political and spatial layout and the lack of a central power defined topographically during the Norman dominion determining the areas of central Italy as the boundary between the southern kingdoms and the Papal States. The numerous castra and fortified structures consequently destroyed and reinforced along the border with the Patrimonium Sancti Petri outline an enormous heritage of proof of the historical–architectural evolution of these border territories. The study of the structures on elevation defines a constructive view which collects the traces of the main transformations of the fortified systems: from the castral enclosures in ruins, passing through the survived ones, although in a state of neglect and embedded in the complex urban systems, to the redefined structures re-examined with the Renaissance perspective and residence castles of the great Roman families