The case of tabella immunitatis discovered in Porto Torres (Italy): characterization of the metal composition

As the inscription suggests, the tabella immunitatis was originally nailed to a ship whose owner was Flavia Publicia, a well-known priestess (Vestale Maxima) in Rome. Her portrait is carved in the central part of the tabella. The inscription says that the ship should not pay taxes in the harbours. This exceptional artefact, linked to one of the most famous Vestales of the mid-3rd century Rome, was analyzed through Energy dispersive X-ray fluorescence spectrometry (EDXRF), integrated by Monte Carlo simulation (MC). The results were integrated by Multiband Imaging techniques (MBI), Total Reflection Fourier Transform Infrared Spectroscopy (TRFTIR), Raman spectroscopy and Optical Microscope documentation. All the analyses were carried out directly in the museum with non-invasive and portable techniques with the aim of maximum protection of this unique artefact. The results obtained provide helpful information to the archaeologists for the study of the piece itself and the comparison with other known tabellae belonging to the Roman period.