The Tyrrhenian II transgression of ocean water into the lagoon left the Minturno level and complex, a dune barrier of about , dated 125-100 thousand years BP. Behind the beach, deep peat and clay deposits alternating with alluvial sediments evidence the lagoon. It was deepest at the Terracina end diminishing to surface at Cisterna, where beds of travertine, sand fused by volcanic activity, reach the surface. At this time, Latium Vetus had been formed as a volcanic land mass, while Latium Novum was a lagoon, the future marsh.