The Acheron Necromanteion: old identifications, recent theories, new interpretations. The present study re-examines the evidence concerning the use of the complex, which was excavated by Sotirios Dakaris on the hill of Mesopotamon in ancient Thesprotia and was identified with the Acheron Necromanteion. The complex was built in the end of the fourth and the beginning of the third century B.C., and consisted of a central three-aisled building with massive stone walls containing a main room and auxiliary chambers, an underground chamber underneath the main room -variously identified to a crypt, a cistern or a cellar-, three annex corridors and a later open courtyard surrounded by rooms. In 1978, the German archaeologist Dietwulf Baatz considered that the site was a fortified residence of a local ruler, also that the central building was a two-storied tower, where six catapults temporarily stood, in the times of the Roman invasion to Epirus (168/167 BC).However, the architecture, the finds and the stratigraphy has proven that this is untenable. Similarly untenable are various alternative proposals regarding the function of the building, e.g. communal storage building, fortress. Thus, as it is supported by recent geological research, we have maintained the identification of this place with the Necromanteion. Furthermore, a new reconstruction of the ritual actions which were taking place there has been proposed, based on the recent studies which underline the sophisticated architecture of the underground chamber and its unique acoustic characteristics, similar to a modern anechoic chamber, which were certainly relevant to the necessities of the cult of the dead.