The Dionysian Mysteries were one of the most popular of the Mystery Religions, alas they were also one of the most mysterious, due to both their strict secrecy, repression by the authorities and the destruction of many of their local chapters.
The only certainty is that they involved extremely primitive initiations based on the mythology of Dionysos and were considered dangerous by both devotees and critics alike.
However a speculative reconstruction is possible, taking into consideration ancient commentaries and modern archeology.
The basic tenet of the Dionysian Mysteries seems to have been a youth initiation, a ritual induction of adolescents into the adult world of sex, drugs (primarily alcohol), and death. Guidance on how to handle these modes of being seem to have been crucial to the initiations. The gender of initiates is uncertain, some later evidence implies male initiation, while other evidence (mostly from Greece and Rome, most famously the murals of the Villa of the Mysteries in Pompeii) indicates female only initiations.
A structure was apparently given to these initiations through the dramatic rehearsal of the mythic life of Dionysos, in which the initiate took the role of the god.
An important part of the early exported Mysteries seems to have been introduction to wine (and other intoxicants), which must have at this stage included secret craft lore of viniculture and the preparation and use of wine. It was with the exportation of wine that the Dionysian Mysteries first travelled, fixing their character.
Later in 'civilized' or 'sheltered' times it appears adults of both sexes were initiated as well, introducing them to a more 'authentic' and liberating mode of being outside of civilised constraint. This made the cult extremely popular(and secretive). The more the restrained and civilised the culture the more the Dionysian Mysteries took hold.
The ultimate Dionysian initiation seems to have been that of death. Not only exposure to killing, but the exposure to ones own near death and the overcoming of the fear of it. This feature was particularly emphasised in early Rome if contemporary accounts are accurate. In late times this apparently took the form of a terrifying underworld initiation culminating in a mock burial in a tomb. Following this final initiation the initiate was ressurected as a new being and renamed.
Over time the Dionysian Mysteries probably absorbed the remnants of the shamanic initiations and practises it encountered on its travels, rites that seemed to naturally complement the Dionysian ethos and increasingly required secrecy to preserve them. Thus the Mysteries are said to have become a repository of shamanism, particularly seership, magick and the manipulation of the 'life force'. Potions or pharmakon were their particular speciality. This added another role that justified the continued existence of the cult.
A final feature of the cult was its political nature. The Mysteries preserved not only primitive practices but primitive virtues. Particularly those of nomadic freedom and communal ownership. Its initiates sought to maintain these values or to reintroduce them where they were lost.
In addition Dionysos was the god of the common people and the dispossessed (particularly slaves and women) and so the cult often represented their interests. Spartacus the leader of the great Roman Slave Revolt was allegedly an initiate. In addition the Mysteries were used by those in power who wanted a grassroots powerbase either for the benefit of their people or more often for their own ends. Both Alexander the Great and Mark Antony are said to have used the Dionysian Mysteries in this way.
It was this political factor, along with fears of anti-social atavism and criminality, which led to a climate of paranoia in Rome around 186BC. This led to the creation of stories regarding the Dionysian Mysteries, which accused them of being involved in secret orgies, sadomasochistic activities, sexual perversion, criminality, drug taking, murder and poisonings, blackmail and general subversion. This was probably a smear campaign but there is also the possibility of some perversion of the Mysteries in repressive, patriarchal societies like Rome. The result of this campaign was the arrest of the male leadership of the Mysteries and the execution of thousands of women who belonged to the cult. From then on the Roman Dionysian Mysteries were strictly regulated each thiasos ('lodge' or 'coven') had to be registered and consist of no more than a dozen initiates. The mythology of Dionysos Bacchus was also remodeled into the tame and safe tales of the chubby Bacchus of Roman Classicism and his joyous romps. Secretly however some of the thiasos no doubt carried on as usual, and these changes failed to effect Dionysianism elsewhere. The nearest equivalent to this in the Greek world was the creation of Athenian Dionysos Societies, which despite their name were little more than men only clubs (with fees and strict rules of membership) where rowdy Greeks could safely be allowed to let off steam.
A unifying thread in the Dionysian Mysteries was a belief in a holistic natural relationship based on a system of dynamic flux and natural cycles, into which initiates were inducted. Though this was based on a vision of nature 'red in tooth and claw' where equilibrium depended on conflict rather than a fluffy ecological vision. The metaphysical content of the Mysteries remains unknown, lack of any sign of a universal belief system has led to speculation that, apart from practical knowledge and craft skills, the Mysteries imparted no dogmatic teachings but rather initiated people into the 'realities' of nature and let them supply their own interpretations. It is thus likely that many schools of thought existed within the cult.
Later the Greek Dionysian Mysteries became more mystical and speculative. According to one interpretation, later posited by Nietzsche, they became concerned with a balencing of chaotic Dionysian forces and Apollonian human creativity and order that made an ideal life possible. They accordingly sought to transcend slavery to nature with a non-repressive creative sublimation of it. This phase called by some writers the Orphean phase (after Orpheus who was a key mythic figure within it) is said by some to be the apex of Dionysianism. More mystical trends in this Orphean School sought to transcend all dualism and reach a higher unity (or so claimed later esotericists).
What is known for sure is that it was from this Orphean School that the Orphic Mysteries and Orphism emerged.
Dionysos, Karl Kerenyi
Dionysos, Walter Otto
Mystery Religions, Jocelyn Godwin
Dionysos at Large, Marcel Detienne
Cults of the Roman Empire, Turcan
Ancient Mysteries, Ed. Meyer
Secret Teachings of All Ages, M P Hall