A knot in a network: Residential mobility at the Late Iron Age proto-urban centre of Basel-Gasfabrik (Switzerland) revealed by isotope analyses

The Basel-Gasfabrik site (Switzerland) is among the largest and best investigated proto-urban centres of the La Tène period (chiefly La Tène C2/D1; 200/150-80 BCE). Excavations revealed evidence of an urban lifestyle, crafts production as well as a multitude of imported goods. Human skeletal remains were recovered both from two cemeteries and from various settlement features. Strontium (87Sr/86Sr) and oxygen (δ18Op) isotope analyses aimed at an assessment of the role of residential changes in the makeup of the site's population, the positioning of Basel-Gasfabrik in local, regional, and long-distance networks, and the exploration of possible correlations between the complex mortuary practices and the individuals' residential history. The study involved 94 enamel samples from 54 human individuals, while archaeological animal teeth and modern vegetation and water samples provided baseline information. The 87Sr/86Sr and the δ18Op ratios of the human teeth varied widely between 0.70755 and 0.71655 and 14.7 and 19.3 ‰, respectively, with more variation among adult males and females than among juveniles. Both the archaeological setting and the isotope data attest to lively contacts of the central site to its hinterland, but also to distant regions, such as the Mediterranean. Differences in the isotope data of successively formed tooth crowns of some of the adult population point to residential changes in childhood. Possible explanations include fosterage as an important element in strengthening regional and interregional ties among Iron Age communities, settlement centralization, and mobile animal husbandry practices. However, areas of origin or patterns of mobility were not among the key factors which shaped the complex mortuary practices.