Comparative regional stable isotope analysis reveals fluctuations in millet consumption during the Bronze and Iron Ages in the Eastern Adriatic

This study presents the largest regional-scale stable isotope investigation of human and faunal remains spanning the Bronze and Iron Ages (c. 2400-100 BCE) in the Eastern Adriatic to date. New δ¹³C and δ¹⁵N data from 51 individuals were integrated with previously published results (n = 233) to explore long-term and region-specific dietary trends, with a focus on the emergence of millet as a dietary component. Results reveal an inland-coastal contrast: while coastal populations predominantly consumed C₃-based diets, inland groups show consistently higher δ¹³C values indicative of direct millet intake from the Middle/Late Bronze Age onwards. Statistical analyses confirm strong effects of both period and location on δ¹³C values, with most inland populations exhibiting more positive signatures particularly during the Middle/Late Bronze Age transition and again in the Iron Age. A probabilistic two-endmember mixing model estimates millet contributions reaching up to ~ 40% of dietary protein in these inland groups, suggesting episodic but significant integration of C₄ crops into subsistence systems. In contrast, faunal baselines reflect purely C₃ diets, indicating that the C₄ signal in humans derives from direct millet consumption. These findings help refine the chronology of millet adoption in the eastern Adriatic, pushing its significant dietary incorporation back to the Middle/Late Bronze Age transition, and highlight fluctuating patterns of C₄ plant consumption through the Bronze and Iron Ages, likely shaped by ecological conditions and local adaptive strategies rather than uniform cultural change.