Increased C4 cultivation and consumption as an impetus for population growth at Badia Pozzeveri, Italy (11th–13th centuries CE)

The focus of this study is to target the paucity of bioarchaeological information related to the population growth that characterized the Late Middle Ages in Italy. Specifically, we used stable isotope analysis to investigate the potential dietary changes caused by this phenomenon in a medieval population (11th–13th centuries CE) from Badia Pozzeveri (Lucca), Tuscany, Italy. Bone collagen from both ribs and long bones of 44 individuals was analysed for bulk carbon (δ13C) and nitrogen (δ15N) isotopic values and a subset of 10 individuals for sulfur (δ34S) isotopic values. Human δ13C values range from −20.1‰ to −13.4 ‰, with a mean value of −17.2 ‰ ± 1.5 ‰. The human δ15N values range from 7.4 ‰ to 11.2 ‰, with a mean value of 9.6 ‰ ± 0.8 ‰. The human δ34S values range from 7.6 ‰ to 10.8 ‰ (mean value 9.2 ‰ ± 1.2 ‰). The isotopic results indicate that the diet was a mix of C3 and C4 terrestrial resources, with possible small inputs from freshwater resources of the nearby Sesto Lake. Isotopic offsets between the ribs and long bones found that 15 individuals experienced a dietary change over the course of their lives. Thanks to a well-defined stratigraphy that distinguishes between phase one (11th century CE) and phase two (12th–13th centuries C), the isotopic evidence of this study indicates an increased reliance on C4 plants, likely millet, during the 12th–13th centuries CE in northwest Tuscany. This suggests that there was a gradual shift from C3 resources to millet consumption, likely in response to the increasing population of this region during this period.