Survey experiences of city walls of Alessandria and Lucca: an overview

In military architecture, the city wall between towers or bastions have architectural-structural characteristics related to the defensive and offensive systems used. Such systems are boundaries of fortified cities at urban scale and differ in shape and size, structure, style, layering of techniques, and territorial relationship to the city. These distinctive elements may include tunnels built to facilitate the passage of people and armaments through networks of passages within the walls. In addition, given the urban scale of city fortifications, they present a peculiar relationship with neighbouring vegetation. This latter requires ongoing control and maintenance to avoiding pervasive vegetation harmful to the wall's preservation and visibility. These artefacts are complex subjects to study through digital survey techniques, given their size, articulation and urban contextualisation. Integrating active and passive methodologies makes it possible to control these architectural structures' morphological complexity and scale variation while preserving their detail and overall accuracy. Within the PRIN 2022 INFORTREAT project, we had the opportunity to survey portions of two different case studies: the walls of the citadel of Alessandria and the walls of Lucca. Each case study presented its own set of challenges in the 3D acquisition process, which we overcame through the application of established surveying processes. The initial comparison of the surveys underscores the significance of employing methodologies that incorporate metric control to ensure the reliability of data on these architectural systems. Another key aspect pertains to the knowledge derived from these surveys, which deepens our understanding of the different building systems and lays the groundwork for a comparison with the principles outlined in military treatises. Furthermore, the optimisation of these surveys provides a foundation for the modelling of forms using parametric tools.