A multidiciplinary investigation of Roman bricks from Torre Civica-Pavia (NW Italy)

A small group of Roman bricks, which had been reused in the medieval Torre Civica of Pavia and recovered from its debris after its collapse in 1989, was investigated by normal archaeological procedures, X-ray diffraction (XRD), optical microscopy of thin sections and instrumental neutron activation analysis (INAA), together with controls: a Roman brick from an archaeological excavation alongside the tower in Pavia and a modern brick. The study aimed 1) to investigate the application of INAA to the study of ancient fired building material, 2) to study brick production in Roman Pavia, and 3) to assess the significance of information provided by archaeological classification and qualitative petrological analysis in relation to INAA characterisation studies. There was no correspondence between the fabric groups identified by archaeological procedures and those identified by optical microscopy. XRD provided information on the variations in mineral composition which could best be explained by differing firing conditions. INAA suggested that the Roman bricks were homogeneous, which was confirmed by their rare-earth patterns; this may derive from the use, in their manufacture, of clay of the same geolithological type - perhaps from the deposits of the Oltrepò south of Pavia, the major source of clay for the city in more recent times. The project clearly identified the applicability of INAA to ancient fired building materials, and gave useful clarification of the reciprocal information provided by different analytical approaches and techniques.