Mapping the origins of Imperial Roman workers (1st-4th century CE) at Vagnari, Southern Italy, using 87 Sr/86 Sr and δ18 O variability.

Abstract

We obtained the oxygen and strontium isotope composition of teeth from Roman period (1st to 4th century CE) inhabitants buried in the Vagnari cemetery (Southern Italy), and present the first strontium isotope variation map of the Italian peninsula using previously published data sets and new strontium data. We test the hypothesis that the Vagnari population was predominantly composed of local individuals, instead of migrants originating from abroad. We analyzed the oxygen (18 O/16 O) and strontium (87 Sr/86 Sr) isotope composition of 43 teeth. We also report the 87 Sr/86 Sr composition of an additional 13 molars, 87 Sr/86 Sr values from fauna (n = 10), and soil (n = 5) samples local to the area around Vagnari. The 87 Sr/86 Sr variation map of Italy uses 87 Sr/86 Sr values obtained from previously published data sources from across Italy (n = 199). Converted tooth carbonate (δ18 ODW ) and 87 Sr/86 Sr data indicate that the majority of individuals buried at Vagnari were local to the region. ArcGIS bounded Inverse Distance Weighting (IDW) interpolation of the pan-Italian 87 Sr/86 Sr data set approximates the expected 87 Sr/86 Sr range of Italy's geological substratum, producing the first strontium map of the Italian peninsula. Results suggest that only 7% of individuals buried at Vagnari were born elsewhere and migrated to Vagnari, while the remaining individuals were either local to Vagnari (58%), or from the southern Italian peninsula (34%). Our results are consistent with the suggestion that Roman Imperial lower-class populations in southern Italy sustained their numbers through local reproduction measures, and not through large-scale immigration from outside the Italian peninsula.