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Abstract The presence of the Early Bronze Age Avellino (AV) tephra in the Holocene lacustrine deposits of the Agro Pontino and Fondi basin provides a unique opportunity to reconstruct the Holocene depositional environment at the time of AV-tephra deposition. Marine terraces of the last Pleistocene transgression have been consolidated by soil formation and incised during the last glacial. This created a gully landscape in the Fondi basin and in the southeastern Agro Pontino. The inland central part of the Agro Pontino was drained by one major gully. At the final part of subsequent Holocene sea level rise, beach ridges closed the southeastern marine lagoons, creating a lacustrine and marshy environment. Shortly after, the Avellino eruption deposited its sandy tephra in these freshwater environments. By comparing altitudes of the AV-tephra in different environments two major implications emerge. First, at those locations where the AV-tephra is underlain by thick Holocene peaty and clayey deposits, significant subsidence occurred, while this has been limited at locations where the Pleistocene marine terrace occurs close to the surface. This subsidence is independently checked by comparing a modern LiDAR DEM and a detailed DEM from 1928. Second, the altitude of the AV-tephra reflects sea level in the coastal positions around −1.5 to −2 m a.s.l., while the only gully draining the lacustrine and marshy inland Agro Pontino was blocked around 0.5 m a.s.l. by the expanding sediment wedge of the Amaseno River, the major draining axis of the Agro Pontino. The AV-tephra layer will continue to play an important role in regional geological, palaeoenvironmental and geo-archaeological research. [ABSTRACT FROM AUTHOR]