The travertines on which the ancient town of Paestum was built about 2,600 years ago, have been investigated to restore the original sedimentary environment of these freshwater limestones formed during the Late Pleistocene–Holocene in the southern sector of the Sele River plain. For this purpose, the few present outcrops of travertine have been analysed from a palaeoenvironmental point of view, integrating the morphology and the sedimentology of the substrate with the information on the textural patterns of the blocks forming the town walls, some of which have a clear similarity with the outcropping substrate. The Paestum travertines can be distinguished into two sedimentary units: the lower Paestum travertines (LPT) which formed between Late Pleistocene (75,000 years BP) and the Early Holocene, and the upper Paestum travertines (UPT) formed during Late Roman to Medieval times. The UPT reached various meters of thickness within the southern and western part of the town, obstructing completely its western entrance, Porta Marina, with its flanking side towers, and were largely removed during archaeological excavations that started in the 1930s. A possible mechanism for this fossilization calls for a process of progressive upward growth of an incrustation barrier within the door, while the calcariferous waters were flowing out from the town at increasing heights.