Millstone coastal quarries of the Mediterranean: A new class of sea level indicator

The coasts of Italy still preserve several remnants of coastal quarries built in antiquity, that now provide insights into the intervening sea-level changes occurred during the last millennia. In this paper, we show and discuss a new class of sea level indicator consisting of millstones carved along the rocky coast of southern Italy since 2500 BP, that are currently submerged. They were extracted from beachrocks, sandstones or similar sedimentary rocks, easier for carving by ancient carving tools. Our study focuses on 10 coastal sites located at Capo d’Orlando, Avola, and Letojanni, in Sicily; Soverato, Tropea, and Capo dell’Armi, in Calabria; Castellabate, Palinuro, and Scario, in Campania; and Polignano San Vito, in Apulia. Unfortunately, only limited archaeological information is available for these anthropic structures. Scario, one of these millstone quarries discussed here, has been dated through independent archaeological remains, allowing us to restrict the exploitation age to the end of XVII century. Present day elevations of these coastal sites were obtained through geo-archaeological surveys calibrated using the nearest tidal stations, together with geomorphological and tectonic interpretations. Data were compared against the latest sea level predictions based on glacio-hydro-isostatic models. Our results allow proposal of the age-range of these millstone quarries and to estimate the intervening relative sea level changes since the time when they were carved.