Archaeometric study of the Roman marbles reused in the late Antiquity St. Saturnino Basilica (Cagliari, Italy)

The St. Saturnino Basilica (Cagliari, Sardinia, Italy) rises over a sacred site since the origins of the town of Cagliari. The original sepulchral function of the area were consolidated and implemented during the Roman Empire and it became a Christian cemetery after the martyrium of St. Saturnino (beginning of the IV Century A.D.). In this period the original chapel of the church was built starting a long evolution of the building across half a millennium, until its Romanesque evolution. The basilica was abandoned and partially destroyed at the beginning of the XIV Century. The formal technical reading of its architectural structure and elements is complicated by the frequent reuse of Roman artifacts during the Byzantine and Romanesque phases as well as the presence of diachronic source materials. The naked-eye analysis of geomaterials present in the monumental highlights a significant number of lithologies (i.e., various kinds of limestones and sandstones, marbles, volcanic rocks, etc.), some of which are in an advanced state of alteration. We present the results of a multi-method archaeometric study (mineralogical-petrographic observations on thin sections, XRF trace elements analysis and 18O vs. 13C stable isotope ratio investigation) concerning the architectural stone elements reused in the basilica between the late Antiquity and Romanesque periods. The majority of lithologies belongs to the local outcrops of Cagliari Miocenic geological formation (e.g., limestone and sanstones). The provenance study has focused on classical marbles used for manufacturing Roman architectural elements (column shafts, bases, capitals, pilasters, slabs, etc.), which are thought to come from extra-regional sources. All the different macrofacies of marbles were sampled taking precise reference to the various construction phases and structural changes of the monument occurred in the centuries. The preliminary results show that the marbles come mainly from Apuan Alps (Italy) and subordinately from Greek quarrying areas.