The Mysteries of Samothrace were open to all: men and women, freedmen, and slaves, poor, and wealthy, commoners and royalty. As the Mysteries’ prestige grew, the authorities attempted to include numerous mythological heroes to the list of initiates (Heracles, Cadmus, Orpheus, the Dioscuri, and every hero who sailed with Jason on the Argo). However, there was no single occasion or date for the initiation. Samothrace being an island in the middle of the Aegean Sea, initiation was possible only during the sailing season (April to November). Still, prospective initiates could attend the ceremony whenever during all these months.

Nevertheless, some occasions were more critical than others, and the festival in June seems to have been the most auspicious time to participate in the Mysteries. The Mysteries of Samothrace had no family of priests comparable to the Eumolpidae and Kerykes of Eleusis. Many natives spoke a form of Thracian, while others used Greek. 

The sanctuary was located close to the city of Samothrace, so it is possible that the initiation began with a procession. The sanctuary entrance was in the east, like Eleusis, and there was an impressive Propylon that spanned the deep stream that formed the sanctuary’s boundary. Another similarity with the Eleusinian Mysteries was the initiates’ obligation to listen to a proclamation banning those whose hands were stained with blood. This was a time of great moral agony for the initiates, made even worse by a priest in the Roman period who asked them to declare the worst deed that they had ever committed. As soon as the initiates entered the sanctuary, they came to a circular space paved with flagstones and surrounded by a grandstand of five steps. This so-called Theatrical Circle is one of the oldest permanent structures in the sanctuary and was adorned with 22 statues (only the bases survive). 

The sacrifices that were such an indispensable part of ancient Greek mysteries took place in the Hall of Choral Dancers; a large, enclosed building decorated with a frieze depicting 900 dancing maidens. The preferred victim was a ram, while libations played a prominent role in the initiation rites. The initiates either brought a bowl or received one from the priests. Thousands of sherds discovered during the site’s excavation serve as a lively reminder of the libations that took place in this magnificent hall.

In Eleusis, the actual initiation took place in the Telesterion. There must have been a building for the initiation in Samothrace, but we do not know which building served this purpose. Unfortunately, archaeologists have been unable to find any trace of the two famous “masculine images [naked men] of bronze before the doors” of the initiation building described by Varro, who visited the island in 67 BCE. According to Hippolytus, “the statues mentioned above are images of the primal man and of the regenerated, spiritual man who is in every respect consubstantial with that man”. The initiates entered the building at night, carrying torches or lamps. There is no information on what happened once they were inside the hall. All we know is that ecstatic dances followed the initiation. The fourth-century historian Ephoros mentions a search for Harmonia as part of the Mysteries (Cadmus kidnapped her when he sailed past the island). 

At the end of the initiation, the participants received a purple fillet. The initiates could bind this fillet below the abdomen in memory of an episode involving Odysseus, who was saved from a terrible storm at sea by placing a veil (since no fillet was handy at the time) below his abdomen. This episode reveals the primary goal of the Mysteries, i.e. to save sailors at sea (rather than secure a better future for the initiates in the afterlife). The sanctuary was full of votive tablets dedicated by grateful sailors, while a wealthy individual was able to dedicate a real warship. The receipt of the fillet was a cause of great joy for the initiates, but the ceremony’s final act must have been a great feast. Otherwise, there seems to be little reason for the numerous banquet halls and dining rooms discovered in the sanctuary. On their way out, the initiates discarded their libation bowls and lamps. In addition to the fillet, they also received a magnetic iron ring (some were subsequently coated with gold and became known as “Samothracian rings”). 

Sometime after their initiation, those interested in a deeper understanding of the Mysteries could attend the epopteia. The ritual must have included preliminary purification rites and sacrifices, as well as a sacred tale of a scandalous nature regarding the sexual arousal of Hermes upon seeing Persephone, as well as the story of the rape of Demeter by Iasion on Samothrace. A certain Isidorus, who came to the island from Athens, left a description of the climax of the epopteia: a spectacular light reminiscent of the ritual in Eleusis.

The most significant problem of the Mysteries is the nature of the Samothracian gods. The islanders called them “the Gods” or “Great Gods”. This anonymity was problematic for those who came from afar, so visitors tended to identify these anonymous gods with deities familiar to them. Herodotus and Stesimbrotus identified them with the Kabeiroi, while other Greeks and Romans called them Korybantes, Kouretes, Telchines, Daktyloi etc. Mnaseas of Patara, who lived around 200 BCE, referred to three deities and called them Axieros, Axiokersa, and Axiokersos. He identified them with Demeter, Persephone, and Hades (an interesting correlation since two of the names are male and one female. The identification with the Eleusinian deities indicates a strong Eleusinian influence). There is also a reference to a fourth god who served the other three as an attendant; his name was Kasmilos, and he was identified with Hermes. The triad of deities seems to have been of great importance, even though their names could vary, and there was no standard iconography to help shape and cement the tradition.