From Roman to Romanesque, a mix of architectural styles and geomaterials in San Saturnino Basilica (Cagliari, Italy): petrophysical characterization, static-structural analysis and 3D laser-scan relief

The Basilica of St. Saturnino rises over a sacred site since the origins of the town of Cagliari. The Roman Empire recognized the importance of such place implementing the original sepulchral function consolidating the function of the area. The martyrium of St. Saturnino (beginning of the IV Century A.D.) signed its passage from pagan to Christian cemetery. In this period the original chapel was built starting a long evolution of the building across half a millennium, until its Romanesque evolution and its later abandon and partial destruction at the beginning of the XIV Century. Its further story continued across time, bringing to our age a rich and interesting monument, articulated around its original structure mixing parts from the Imperial Roman, Byzantine and Romanesque phases together with clumsy attempt of modern restorations. The Byzantine phase has left us a large cubic structure, with robust arches and vaults testifying the evolution of construction techniques in Medieval Sardinia. The formal technical reading of the elevations is complicated by the frequent reuse of Roman artifacts, often of exquisite workmanship. The presence of diachronic source materials, together the technical problems of attribution, often make it difficult to study the building. The analysis of materials has led to a thorough investigation of the macroscopic number of lithologies, some of which are in an advanced state of alteration. To start a clear reading of this complex system a multidisciplinary approach was chosen, combining historical reading, analysis of the stones and digital survey solutions. The most significant materials in the church were sampled, taking precise reference to the various construction phases of each historical context and interventions of structural changes occurring in the various centuries and numerous restorations mirror of philological different cultures. The whole building and its surrounding area were surveyed with the following methods: photography, 3D Laser Scanner for the whole interior and exterior parts, 3D photogrammetry of a selected set of stone surface samples. Were sampled and geochemical and petrographic analyzed several architectural stone elements (shafts of columns, capitals, etc.) used as building materials, characteristic of the Roman period, made in various kinds of marbles, currently distributed between the inside and outside of the monumental structure. Were also analyzed carbonate rocks ("pietra cantone", "pietra forte" of the Cagliari formation), used to make the most of the perimeter walls. To a lesser extent, there are ashlars of Oligo-Miocenic volcanics of Sardinia, and the occasional presence of other stone materials coming not from the island. A complex system of traces in need of contemporary and well organized digital and scientific approach in order to enhance the knowledge about this monument. The contribution proposed here will present the progress state of this research and its results