Pistoia, city of stones

Pistoia, bordered to the north by the slopes of the Apennines and to the south-west by Monte Albano, is characterized by its long walled perimeter inside which many gardens and green spaces alternate with buildings in such a way that the urban space preserves the aspect of the pre-industrial city where Romanesque, Gothic and Renaissance forms coexist. In the urban plan, the phases of development between the VIII and XIV century are clearly recognizable. There is little information about the primitive Etruscan settlement of the VI-V century BC when the current Piazza del Duomo was the starting point for the trans-Apennine routes. More certain are the news of the Roman Pistoia, a colony built along the Via Cassia which constituted the decumanus maximum. The city has a varied stone heritage that reflects only in part the lithological nature of the surrounding hills; mineralogical an petrographical analyses have partially confirmed the origin. The main building material is the Pietra Serena sandstone that is present extensively in the surrounding mountains and has been used as large pebbles, ashlars and architectural decoration. Secondly there are bricks, found in mixed masonry, for the construction of load bearing arches and for the construction of Santa Barbara Fortress. Regarding decoration and cladding, materials close to the city are the serpentinite from Monte Ferrato, near Prato, the travertine of Monsummano, the Rosso di Monsummano present inside Santa Maria dell'Umiltà and the Pietra Alberese from the nearby hills. About this limestone, it is possible that part of this material is not real Pietra Alberese but Calpionelle Limestone or limestone from the Mesozoic nucleus of Monsummano. Micropaleontological analyses on microsamples are in progress in order to verify the exact origin. In some churches there is also the Pietraforte sandstone and this is quite strange because the outcrops of this lithotype are found in the hills south of Florence, therefore quite distant. Another peculiarity is the use of Montagnola Senese marble in the cladding of Baptistery. The knowledge of the exact nature of the materials is important to learn more about the construction history of the city but also to understand the decay phenomena and to select the most suitable conservation interventions.