Chemical tracers of Lusitanian amphorae kilns from the Tagus estuary (Portugal)

In this paper, the characterization of Roman amphorae from the Porto dos Cacos (PC) and Quinta do Rouxinol (QR) workshops, in the Tagus estuary, dating to a period between the 1st and 5th century AD was carried out on the basis of instrumental neutron activation analysis data on 260 amphorae fragments, together with mineralogical compositional studies obtained by X-ray diffraction.Special attention was devoted to the study of the Dressel 14, Almagro 50/51c and Lusitana 3/9 amphorae in an attempt to establish whether or not it is possible to establish any correlation between the composition and typology, and between and within the production centres studied.A description of the geochemical patterns associated with each production centre was first carried out separately, followed by a discussion comparing the two centres situated in the same sedimentary basin, identifying diagnostic chemical tracers for each one; also, in certain cases, a relative correlation with the typology was achieved. Both the definition of reference groups and the attribution of amphorae to their workshop origin relied on the use of chemometric techniques for data structure analysis, coupled with geochemical data analysis, especially regarding trace element data and its geochemical behaviour and distribution according to the geological environment of the region.This approach complements and reinforces the conclusions drawn from typological and archaeological analyses. Considering the two kiln sites studied, we may talk of the production of two types of Roman amphorae in the lower Tagus, with the establishment of compositional groups defined according to their corresponding chemical signatures. The products of the PC workshop are characterized by high concentrations of Co, As and U, and low concentrations of Fe, Zn, Sb, Rb, K; QR workshop amphorae show instead higher concentrations of Fe, Sb, and also of Rb and Zn, and lower amounts of U.These results make it possible to understand the crucial importance of the lower course of the Tagus River within the framework of the analysis of the economy of the estuary at the time. This, in turn, may lead to a better understanding of production and trade within Lusitania and also with other Roman provinces.