The Pertosa Caves, today also known as the Pertosa-Auletta Caves, constitute an important karst system in the Campania region (southern Italy). Crossed by the waters of a river that re-emerges on the surface, they have an overall development of about 3 km. Thanks to the width of the entrance, the excellent location along a natural communication route through the mountains and the natural availability of water directly on the site, the initial part of the cavity was frequented by humans, without interruption, from prehistoric times to the Middle Ages. During the protohistory, in particular, the moment of most marked human presence is recorded in the cave. In this phase an extensive pile dwelling system was built on the waters of the underground river. The system was probably created to make the location, subject to frequent flooding, suitable for human settlement. This structure today constitutes an archaeological unicum not only in Italy but throughout Europe. We briefly analyze its general characteristics providing the results of a radiocarbon dating campaign which allowed to assess the occupation phases of the different contexts and the life span of the wooden artifacts, which came to us in a very good state of preservation. Radiocarbon data allowed to assess the chronological range of the human frequentation of the caves and to date the exceptionally well preserved underground pile dwelling system.