Forty years ago the Greek archaeologist Sotirios Dakaris discovered a remarkable late fourth- or early third-century B.C. building complex on the hill of St. John Prodromos (John the Baptist), which rises above the Acheron River about 1.5 miles from its mouth at Phanari Bay in Epirus, northwestern Greece.

Its central structure was 72 feet square with extraordinarily thick (about 11 feet) walls of carefully fitted polygonal stone blocks. Below this Dakaris found a subterranean chamber. He identified the building as the famous Nekyomanteion, or Oracle of the Dead, to which Periander, tyrant of Corinth in the sixth century B.C., had sent emissaries to consult his dead wife, Melissa, as recounted in Herodotus.

Dakaris believed it to be the place Homer had in mind in his account of the visit of Odysseus to "the Halls of Hades and Dread Persephone" to consult the dead seer Tiresias about how he might return to Ithaca. The remains of the Nekyomanteion have been preserved.

The ancient Greeks believed that the dead (in Greek: “Nekys”, “Nekroi") stayed in the earth as a perishable body while as a soul they were released and found their way to the Underworld through deep gorges, crevices and caves. The souls of the dead did not have ordinary consciousness but had other capabilities not possessed by the living such as the ability to know the future.

Based on such beliefs, the Homeric Odysseus descended to Hades, [the world of the dead], to meet the soul of Teiresias the great diviner to find out what was hidden in his future. In the rhapsody “Nekyia” of the Odyssey we have exact descriptions about the care that should be exercised by the living when approaching the souls of the dead, since the miasma of death was very powerful.

Faith in such beliefs led many among the ancients to visit sites, which were reputed to be entrances to the Underworld in order to receive prophecies from the Oracles of the Dead ("Nekyomanteia") established in these locations. Among the more famous were the temple of Poseidon in Taenaron as well as those in Hermione of Argolis, Kyme in Italy and Herakleia in Pontos. Yet the most important Nekyomanteion by far was the one at Lake Acherousia and the three rivers of Hades, near the Thesprotian city of Ephyra, at the place were according to tradition Odysseus communicated with the dead.

Excavations unearthed a building complex with a rectangular courtyard surrounding a square building, from the 4th century BC, which functioned as the temple and consisted of a central hall with side aisles. Below the central hall was an underground chamber cut into the rock, presumably at the location of an ancient cave. This served as the pitch-dark palace of Hades and Persephone. The arches supporting the roof of the chamber were also the foundation for the floor of the upper chamber. The continuous corridors at three of the sides and the rooms to the north and east have also been attributed to the 4th century.

Later, a central court was added to the west as well as more rooms for the pilgrims. From the north gate the pilgrim would pass to the northern corridor and to the left he saw two rooms and a washroom, which would serve him during the period of bodily and psychological purification, which inevitably preceded the entrance to the sanctum.

For a certain period of time, and in total darkness, the pilgrim ate food appropriate for the dead such as broad beans, pork, barley bread and oysters and underwent purification by washing and prayers.

The purpose of these procedures was presumably to strengthen the pilgrim’s defences against the psychologically powerful contact with the death experience. With yet more severe fasting and meditation the pilgrim would also stay in the northern room of the eastern corridor until the time of the oracle.

Then, together with a priest, he would enter the eastern corridor, would sacrifice a sheep and then, holding bloodless offerings in his hand, he would follow a meandric corridor with three ironclad gates, as many as the gates of Hades. He would leave some of his offerings there, and would offer the rest in the central hall, which was the place where the souls of the dead would appear. During the whole process the priest would chant prayers and evoke the dead. The long preparation in such an imposing environment, and the special fasting [and meditations] together with the faith in the appearance of the dead would induce the pilgrim to see the shadows of the dead. The 4th century, however, was a rational century, with less possibility for the psyche of the pilgrims to experience the miracle, so the Oracle took appropriate measures as discovered by the excavations.

Specifically, at the end of the central hall, at the place where the images of the dead were to appear, the archaeologists found wheels, copper catapult gear and ratchets which probably indicate the presence of a crane, which had a human image at one side and a counterweight at the other.

The latter were discovered in an adjacent room. Anyway, the pilgrim would exit from the opposite side and would then undergo a three-day purification procedure. From then on he was expected to keep absolute silence about what he had seen and heard and the penalty for revealing the mysteries of Hades was death.

Various votive offering by the faithful have been found dating from the 7th century BC and thereafter, however, it is evident that with the construction of the Hellenistic temple most of the artifacts from the previous period were destroyed. The Romans burned the temple in 167 BC, but traces of habitation after the 1st century have been discovered in the area where the courtyard used to be.