Settled farmers or mobile herders? Patterns of mobility at Shahr-i Qumis, a late antiquity site in northern Iran, investigated using strontium isotope values

Little is known about human mobility in the Iranian Central Plateau during the Parthian and Sasanian periods. To fill this gap, we measured ⁸⁷Sr/⁸⁶Sr values in 22 human enamel samples from Shahr-i Qumis, Semnan Province, retrieved from collective burials in the ruined buildings of an abandoned capital city of the Parthian state. The skeletons were radiocarbon dated to the Late Parthian and Sasanian periods. The results were compared to ⁸⁷Sr/⁸⁶Sr values measured in 41 plant samples and 3 snail shells collected from spots along the southern slopes of the Alborz Mountains between Qazvin Plain in the west and the Jajarm Plain in the east. All but one of the ⁸⁷Sr/⁸⁶Sr values in human teeth are consistent with local strontium isotope values, and therefore the skeletons likely represent people who did not change their location between infancy and death. This suggests that the cemetery was used by a relatively immobile population of farmers who took advantage of the favourable conditions at the alluvial fan for crop cultivation or stationary animal husbandry, rather than transhumant/nomadic pastoralists who would have used larger and more distant areas as pastures.