Systematic sourcing of granite shafts from Gallia Narbonensis and comparison with other western Mediterranean areas

International audienceDetermining the source quarries for granite shafts in antiquity provides insight into ancient trade routes for such prized materials. We briefly review how non-invasive techniques are currently being applied to address this archeometric task. In specific cases established protocols based on magnetic susceptibility can be integrated with chemical analysis, as demonstrated herein. A systematic inventory and sourcing of granite shafts of presumed antique origin was performed in the region that once formed Gallia Narbonensis. A total of 276 complete shafts or shaft fragments were identified in 21 localities. After fragment pairing hypotheses, they were attributed to at least 174 original shafts. Only four localities (Aix, Arles, Die, Riez) contribute to 54% of the whole corpus. Provenance was determined through visual, magnetic susceptibility and chemical comparison with known antique quarries in Egypt, Turkey, Elba, Corsica and Sardinia. Most of the shafts originated in Turkey (75%), followed by Elba (20.5%). Minor sources are the pink granites of Aswan and Sardinia, as well as grey granite from Corsica, found only in Die. Ambiguity between the Corsican source and the grey Egyptian granite from Mons Claudianus was resolved using portable X-ray fluorescence to determine Sr and Rb contents. As most of the corpus consists of shafts present in medieval to modern contexts, caution is required in interpreting our findings in terms of Ancient Roman architectural and economic choices. Long distance transport of spolia or newly quarried shafts may have occurred after Roman times