Geoarchaeological sea-level proxies from a silted up harbour: a case study of the Roman colony of Luni (Northern Tyrrhenian Sea, Italy)

The Luni Plain, which faces the northern Tyrrhenian Sea, underwent major landscape changes over the last 3000 years. The coastline shifted south and west, separating the ruins of the ancient Roman colony of Luni (founded in 177 BC) from the sea by means of a new coastal plain. The precise location of the coastline during the main settlement phase as well as during the city’s decline has never been established, although partial and qualitative scenarios have been suggested by various authors. According to these authors, an indentation of the coastline west of the city formed a major water basin, along the shores of which traces of pre-Roman settlements exist; near the city, two minor basins were present, suitable for hosting harbour structures. The city of Luni was famed for its harbour (Portus Lunae), from which the marbles quarried in the Apuan Alps, used to build many of the monuments in Rome, were delivered. The traces of its port, however, are scattered and uncertain. Newly available subsurface data are presented, associated with a revision of unpublished archaeological evidence of the ancient city topography. Progress in palaeoenvironmental reconstructions at Luni has been possible thanks to the collection and analysis of ancient and recent cores, supported by radiocarbon dates, as well as the interpretation of archaeological findings suitable as markers for sea-level recognition. The main environmental changes in the area have been refined: since a few centuries before the colony was founded, the Luni plain had been characterized by a complex architecture of swamps and marshes limited by dune ridges and fluvial sand bars. The positions of these landforms were not fixed, but shifted, mainly depending on the spatial relationship between the coastline and the river mouths. Determining the precise position of the Roman coastline is useful to constrain the area in which archaeological surveys should be concentrated in order to identify the harbour location. Moreover, some of these results have been used to infer altitude constraints on the sea-level position in Roman times: preliminary data are shown for constructing a Late Holocene local sea-level curve in the area.