The pre‐79 CE alluvial environment south of Pompeii's city walls

The environment in the suburban area of Pompeii between Porta Marina and Porta Stabia at the time of the 79 CE volcanic event was investigated by means of a series of core drillings. These revealed the presence of a ubiquitous dark brown layer (referred to as “Phase 2 interval”) immediately below the 79 CE eruption deposits. Its stratigraphic interpretation relied on 14C dates, diatom analysis and micromorphology, and on comparisons and correlations with the available stratigraphic logs and excavation data. Phase 2 interval represents the sedimentary accretion that took place from ca. 900–750 cal a BCE to 79 CE. Its formation is the result of periodic flooding by the Sarno river in this distal reach of its floodplain (i.e., backswamps). The resulting picture is that of a patchy environment with weakly developed alluvial soil juxtaposed to areas with stagnating waters. No indication of artificial or natural watercourses derived from the Sarno river, of navigable lagoons, or of harbor basins was found.