The White Marble of the Arch of Augustus (Susa, North-Western Italy): Mineralogical and Petrographic Analysis for the Definition of its Origin

The Arch of Augustus in Susa (north-western Italy) was built in 9–8 bc by King Cottius, to celebrate the treaty between the Romans and the Gauls. It is made of white marble, which was considered for a long time to be locally extracted, but no archaeometric studies have been performed up to now. Therefore, a multi-analytical study based on petrographic (optical and scanning electron microscopy), electron microprobe and stable isotope analyses was carried out on the marble from the arch and from reference samples, with the aim of defining the provenance. All the data confirmed that white marble belonging to the metamorphosed carbonate cover of the Dora Maira Massif, known as Foresto marble, was used for the Susa Arch. This choice was probably made for economic reasons, but also due to the relative independence of the ruling family of the Alpes Cottiae, which was obviously interested in promoting a local marble.