Stones of the façade of the Sarno Baths, Pompeii: A mindful construction choice

Abstract The lithological analysis of the southern facade of the Sarno Baths, a complex building located in the south-western part of the ancient city of Pompeii (Naples, southern Italy), was addressed to define the types of stone used as blocks and ashlars of the three nearly completely preserved levels. Lithological analysis, coupled with petrographic (optical and electron microscopy) and mineralogical study of the lithotypes macroscopically defined, revealed the use mainly of volcanic and volcano-clastic rocks, and in particular of: (i) yellow tuff supplied from the yellow facies of the Campanian Ignimbrite (about 39 ky BP); (ii) grey tuff from the Campanian Ignimbrite; (iii) leucite phonolitic tephrite from the lava flows of Somma Vesuvius; (iv) travertine from the Sarno limestone (Calcare del Sarno) (Cretaceous). On the basis of the lithological mapping, the basement results mainly composed of leucite phonolitic tephrite, associated to travertine and sporadically to yellow tuff, whereas the other two overhead levels are mainly constituted by tuff and travertine, respectively. In particular, the tuff distribution on the level upon the basement shows a prevalence of grey tuff on the western portion, yellow tuff on the eastern one and in the opus reticulatum band running all along the facade, and marked at the top by a trachyte stringcourse. Travertine blocks in the uppermost facade were probably placed as integration during the restoration works carried out at the end of the 19th century. The distribution on the facade of elements made of different rock types, characterised by different bulk density and mechanical properties, confirms ancient Roman builders’ deep knowledge on the technical features of these materials and their structural behaviour.