Analysis of historical maps as a tool for the protection of the historical walled city of Alghero (Sardinia)

The historical city of Alghero, located on Sardinia northwest coast, still preserves a part of medieval and modern fortifications which construction began during thirteenth century. The medieval defensive line designed by the noble Genoese family of Doria is the object of significant adjustments in the sixteenth century during Spanish Kingdom. The fortress reaches its maximum expansion at the end of eighteenth century during Savoy kingdom; by this time the modern fortifications enclosed the historical city that, washed by the sea on three sides, was further defense by others outworks called ravelin. The decommissions of the fortress (1867) gave the start to the urban grow and determined the demolition of a significant section of the city wall, preserving the sixteenth towers and a part of the military architecture that appeared during recent archaeological excavations. The entire defensive system is accurately described in the drawings of Spanish and Piedmont engineers; it allows an identification of the military structures demolished or buried below the current urban street level. The data derived from the analysis of historical maps also allows to prepare a geographical database that supports the evaluation of the archaeological risk and the planning of any interventions in historical city walled.