Salinity Transition in the Ostia Lagoon During the Roman Period: Assessing the Feasibility of Salt Exploitation

ABSTRACT This study examines long‐term salinity changes in the Ostia Lagoon between the 4th century cal BC and the 6th century cal AD , with emphasis on their implications for ancient salt production. Although Ostia's foundation is closely linked to the control of salt resources in the Tiber Delta, direct archaeological evidence of Roman‐period saltworks is scarce. To address this gap, this study combines micropalaeontological analysis of ostracod assemblages with a morphometric study of sieve pore features in Cyprideis torosa (Jones, 1850). This approach enables reconstruction of short‐term palaeosalinity dynamics. Core LOA–1 documents a transition from peatland to euryhaline lagoon between the 8th–6th and the 4th–3rd centuries cal BC , followed by repeated high‐salinity episodes. A notable peak coincides with the establishment of the Roman Castrum, suggesting favourable conditions for salt concentration. After the mid‐4th century cal BC , salinity peaks decreased, possibly reducing the lagoon's potential for saltworks and fostering greater reliance on the Maccarese saltworks. In the northern lagoon sector, hyperhaline conditions during the Roman period remain uncertain because of chronological gaps and the lack of sieve pore analysis. Overall, the results demonstrate both the potential and limitations of ostracod analysis as a palaeosalinity proxy and refine understanding of salt exploitation in the Tiber Delta. This study provides valuable insights into the long‐term socio‐environmental dynamics of the Mediterranean coastal wetlands, contributing to the advancement of geoarchaeological research on ancient salt production through salterns and its influence on human settlement patterns and economic practices.