Bastion survey protocol: operational activity framework for multi-scale surveys of fortified walls

The fortified heritage is a complex and layered category of Cultural Heritage in which military engineering, architecture and urban history converge. These structures, often monumental and complex, require integrated digital surveying approaches that account for scale variations, aimed at their documentation and preservation. Due to the complexity of these artefacts, surveys must be conducted in a coordinated manner, with control over the entire process and the final reliability of the results depending on the scale. If the latter is urban, it is possible to frame the whole fortified system at a territorial level in its formal entirety. At the same time, at an architectural scale, the individual geometries of the bastions, curtains, casemates, and other elements are documented, providing a general overview of construction techniques, structural conditions, and historical alterations. At a detailed scale, it is finally possible to concentrate on material and technological transformations, focusing on specific surface areas and related deterioration pathologies. These scales can and must be integrated, offering a multi-level reading system capable of rendering the complexity and information stratification of the artefact. It can occur through planning activities that harmonise information within a coherent cognitive framework and through applying a protocol with guidelines to support both the operators and the body that manages the asset, coordinating its management and maintenance activities. Thus, the latter can have a tool to control the quality of the surveys and the consistency of existing data, providing temporal continuity. The authors propose a generalisation of the theme of the survey of bastions, defining guidelines to facilitate the operational phases according to the survey objectives and the scale of the activity.