A multi analytical approach to study ancient manufactured stones

To shed light on the “mysterious” use of some manufactured rocky blocks found in the archaeological site of Pietralba (Pieve S.Stefano, AR, Italy), a multi-analytical investigation was performed. The site is located on the right slope of the deeply incised valley of the Tignana Creek, a tributary of the Tiber River. Along this slope several blocks of sandstone occur as the product of ancient rockfalls. Some of these blocks are carved and despite the high weathering the chisel signs are still visible. According to the pottery found nearby the structures, these latter can be attributed to the Middle Age.Clearly worked “in situ”, they display different shapes : a tub, the letter L, a throne, a pyramid. Even though the wide diffusion of similar manufactured rocks, their use and their age are still unclear though several hypotheses have been put forward: the most credited ones concern uses as water places, plant-mills or for tanning. In this work we report the first results obtained on the Tub block; this manufactured rock displays a depth of few decimetres and is characterised by an open side downslope; possibly, only small volumes of unknown substances were temporarily stored in the Tub. Furthermore, the absence of any source of water at a suitable distance suggests that any treatment would be possible with few or no water solution. Rock samples collected in the Tub were analysed in order to obtain the sandstone mineralogical (XRD analyses) and chemical inorganic composition (XRF analyses). Successively, Fourier Transform Infrared Spectroscopy (FTIR) and Gas Chromatography-Mass Spectrometry (GC-MS) were used with the aim of identifying the presence of organic components.Very interestingly, oily organic substances have been found and, in particular, vegetable lipids, both diterpenic and triterpenic molecules; these latter are often contained in the bark of plants. In order to answer to this important question it could be necessary to comprehend the importance of both the topographic position, the morphology and the vegetable cover and to understand the characteristics of the manufactured rocks, i.e. resistant water tight tanks, located in a dry place, and capable of withstanding the weight of such a type of working. This work presents the preliminary results obtained on different rock samples belonging to the Tub, the letter L, the Throne, the Pyramid.