La Fortezza Veneziana di Bergamo: studi per la mappatura speditiva di 5 km di mura, parte integrante del paesaggio cittadino

The ‘Venetian Fortress’ of Bergamo is a very well-known example of integration of a strong military defensive apparatus in the urban landscape of a living city. The particular configuration of the town, growing over a hill and near the feet of the Alps, make this workmanship particularly impressive, despite the defects that the military architects of the time found very soon. From the moment of his construction during XVI century, by the wishes of the Venice Republic, the great fortification of Bergamo was never attacked. Nevertheless, it created a strong separation between the ‘upper town’, closed in the fortress, and the ‘down town’, that was already developed around the roads connecting the surroundings and was also protected by an old defensive circuits of medieval walls. This situation definitely conditioned the development of the town along the centuries, but allowed not only the survival but also the embodying of the fortress in the town, thanks to a constant care and a peaceful reuse of the military architecture as panoramic promenade and green belt. In the framework of the continuous maintenance project set up by the City Council, funded by Fondazione Cariplo, and the UNESCO 2015 nomination ‘Terra di San Marco’, supported by MiBACT, a specific project was set up in order to survey and control the whole extension of the city walls: more than 5,000 m long, for a wall surface of around 70,000 m2. The automatic three-dimensional survey – with both active (laser scanning) and passive sensors (terrestrial and aerial photogrammetry with drones) – offers new opportunities for metric and material monitoring of landscape and historic buildings, particularly when the overall dimension or the orographic situation are challenging, like usually is in military landscapes. The quick acquisition of spatial geometries, combined with a metric and chromatic high reliability, allows an easy planning of the survey campaigns. If scheduled on a regular and cyclical basis, they can help to build a powerful database providing clear indications about the evolution of degradation appearances, or the occurrence of local instability phenomena and, in general, useful to document the overall situation. In particular, the high-density information allows mapping of cracking, deformations, and material anomalies in an easy manner and in reduced times together with a metrically accurate localization. The information, having a quantitative and not only qualitative character (as can be obtained by an ordinary photographic campaign), lets the operators to plan future activities, establishing whether to call for urgent action (because degradation phenomena had a rapid mutation) or, alternatively, to delay them since any change occurred, which could compromise structure’s functionality and safety. Since summer 2015, a first trial on the complex of the former church and monastery of Sant’Agostino and the surrounding walls has been developed. For covering of the former convent in its entirety, fifteen flights lasting an average of ten minutes were carried out in the closed system of the University campus and the city park of Sant’Agostino. The survey carried out simultaneously on the ramparts and on the complex, usually studied separately, gave the opportunity of new extended reflections at the environmental scale. The results obtained are encouraging in terms of the wealth of gathered information and the possibility of their use.