“Leggere” la cartografia storica: acque e città fortificate dello Stato di Milano dal XVII secolo ad oggi

The paper presents a methodology of analysis and interpretation of cartographic data to understand and reconstruct the historical evolution of some fortified urban systems placed on watercourses (rivers Po, Ticino, Adda and Tanaro) and/or on strategic junctions in Piemonte and Lombardia. The sites, belonging to the State of Milan between the seventeenth and the end of the eighteenth century, are documented in a series of "atlases", cartographic collections and representations that show, at different time, the current state, the transformations and the projects. To these are added, in the following centuries, cadastral maps, cartography of the Military Geographic Institute (IGM), maps and current orthophotos. The border cities of the Duchy of Milan during the spanish domination constitute a field of experimentation for military engineering, both for the precariousness, in many cases, existing defensive works, still late medieval, to be modernized, both to be placed in strategic places on road or lake/river junctions. These cities became the outposts of a redesign and urban experimentation that, even today, characterize their structure even where the walls and castles partly or completely disappeared, as elements of a contradiction in the definition of policies of spaces reuse, compared to current needs. The layered readings with innovative techniques (GIS) of these cartographic materials allow us to reconstruct, through overlaps and comparisons, the transformations of the central area of the cities, directly in contact with the fortified walls and to understand their "permanence degree", not only as a material consistency, but also as a trace, and to understand how much these systems changed over time and influenced or defined the current forma urbis.