Preliminary archaeometric analyses of reused Roman materials: the case of the tower at Via dei Montanini 16 in Siena, Italy

The subject of the present study is one of the two towers, today corresponding to house numbers 1 and 16 in via dei Montanini in Siena (Italy), which constituted the impost structures of an arch, possibly dating back to Roman times, known as the Arco di San Donato, demolished around 1480. In particular, the analysis focuses on the tower located at number 16, which preserves conspicuous remains of materials from a pre-existing Roman structure. These include blocks consisting of brick and mortar elements, carefully squared in imitation of the tower stone ashlars of a later period, and others made of cocciopesto flanked by travertine ashlars, arranged in such a way as to create a polychrome effect visible on a large part of the wall face. The aim of the study was to analyse the brick-mortar blocks and the cocciopesto blocks through archaeometric investigations, with the intent of understanding the composition and production processes, in view of possible conservation interventions. The work uses a multidisciplinary approach combining non-invasive surveys and laboratory analyses. The survey was carried out using a Mobile Mapping System (MMS) based on LiDAR (Light Detection and Ranging) technology, which generated a high-density point cloud useful for mapping the wall surfaces. At the same time, representative samples of the cocciopesto and brick-mortar blocks were taken and subjected to macroscopic observations, mineralogical analyses by X-ray diffraction (XRD) and polarising optical microscope observations for a mineralogical-petrographic characterisation. Preliminary archaeometric analyses attest to the use of local raw materials, offering significant data on building techniques and resource procurement methods in ancient times. The good preservation of the materials analysed suggests the possibility of reconstructing them in the laboratory with characteristics like the original ones.