The bricks of the UNESCO historical town of Urbino (Marche, Italy): characterization, provenance of the raw material and archaeometric dating.

Man used bricks for buildings for thousands of years, but the greatest breakthrough came with the invention of fired bricks (about 3.500 BC). Due to the use of mobile kilns, the Romans strongly contributed to spread the fired bricks throughout the conquered territories. The historical town of Urbino (in the list of UNESCO World Heritage since 1998) is characterized by a very widespread use of bricks in monumental walls, palaces and churches. A collection of brick samples from buildings of different historical times such as the remnants of the Roman period, the Urbino Cathedral (built in a span time between the XI and the XVIII century), the Renaissance walls and some other monuments (Mazzini, 1982; Luni, 1985; Agnati, 1999; Luni & Ermeti, 2001; Negroni, 2005) will be investigated through a comprehensive archaeometric project. Close to the town of Urbino, several raw materials suitable to make bricks, such as fine-grained clayey soils, are present and ruins of ancient furnaces since the Roman period are also recognizable (Luni, 1986). Concerning the Urbino Cathedral, the bricks are representative of numerous diachronic building phases, mainly due to the reconstructions after the seismic events of the XVII and XVIII centuries. The aim of the present work will be the mineralogical and chemical characterization of the bricks in order to define the nature and the provenance of the raw materials employed in their manufacture. Standard thin section and powder XRD methods will be used to identify the different mineralogical assemblages and to establish the reached thermal conditions of firing, whereas major-trace elements analyses (ICP-OES-MS) will be of paramount importance for comparisons with raw materials. Physical and mechanical properties of the bricks (dry bulk density, specific gravity, total porosity and, if possible, uniaxial compressive strength) and also physical properties of the raw materials (grain size distribution and Atterberg limits) will be determined. Finally, thermoluminescence will be used as a powerful method to date the original firing of the bricks (Martini & Sibilia, 2001) in order to constrain a chronology of the various building periods of the architectural structures, coupled with the different pyrotechnological processes and raw materials used through the time.