Isotopic analysis (Sr) in the Necropolis of Castel Sozzio, Viterbo, Italy: study of populational interactions

Abstract

Human mobility corresponds to the natural movement of peoples on a geographical horizon in a defined historical context. Understanding its aspects and dynamics provides a comprehensive picture of how different peoples interact. Oxygen and strontium, like all the natural elements, have a precise isotopic distribution that can be altered by biochemical and environmental factors. What is interesting is that the values of these alterations are characteristic for a given geographical area rather than for another. By examining the concentration of strontium and oxygen and their stable isotopes (atoms with variable mass numbers) inside bones and teeth, it will be possible to obtain information about the population dynamics of the area of interest. Information that will complement a broader study of ancient DNA. The first excavation of the necropolis of Castel Sozzio begun in 1997 and stopped abruptly the following year. In 2020, investigations were resumed under the direction of Prof. Emanuela Borgia (Dipartimento di Scienze dell’Antichità, Sapienza Università di Roma) and the Soprintendenza Archeologia Belle Arti e Paesaggio per la provincia di Viterbo e l’Etruria meridionale. The research conducted at Castel Sozzio, through the joint application of archaeological and anthropological sciences, is aimed to investigate the late antique phases of the area, which witnesses a continuity of occupation between the 4th-5th centuries AD and the 7th century AD. In this historical phase, the interaction between Romans, Goths and Lombards can be assumed in this area; however, the lack of material evidence and the absence of written documents relating to the necropolis site require specific concerning anthropological material, in order to determine or understand more broadly the dynamics of these contacts. With this in mind, an isotopic analysis was carried out on 33 samples, of which 26 were human and the remaining 7 constitute the baseline (samples of: animal bones, plants, soil) allowing us to make a comparison and distinguish local and non-local individuals. Sex and Age studies have also been carried out on the human samples, showing an heterogeneous composition of the individuals buried in the necropolis. Sr isotope analyses were conducted by MC-ICP-MS (neptune) at the Department of Chemical and Geological Sciences of the University of Modena. This made it possible to identify two non-local groups within the necropolis that interact with the indigenous substrate.