"I argue that we can know virtually nothing of certainty about the ancient Druids, so that - although they certainly existed - they function more or less as legendary figures."
Professor Ronald Hutton, in the Introduction to his book, The Druids (Hambledon Continuum, 2007).
As Professor Hutton says, our knowledge of the beliefs and practices of ancient Druids is based on very little hard evidence. Of the few classical writers who mention them at all, even fewer actually knew any Druids, and those who did had particular axes to grind. As for Druids themselves, their reliance on oral learning ensured that they left no written records of themselves, their beliefs or practices. Nor is there a single archaeological find that can positively be identified as Druidic. It might seem, therefore, that any discussion of Druidic history is over before it's begun. Not so.
The evidence from classical writers and from archaeology may be fragmentary, potentially misleading, and open to different interpretations, but it is evidence nonetheless. And then there is the whole recorded history of the various Druid revivals that have taken place from the 16th century to the present day. Beyond that, there is the evidence of our own instincts, intuitions and visionary experiences.
It is our belief that ancient Druids represented a priestly caste within the society of Iron Age Europe, fulfilling roles as seers, teachers, counsellors, lawyers, judges, philosophers and priests. In other words, their roles were similar to those of shamans in other cultures, relying on communication with spiritual realities.
In the various Druid revivals that have occurred over the last few centuries, Druids have been variously portrayed as inheritors of the faith of Atlantis, biblical patriarchs, sun-worshippers, Freemasons and a wide range of other forms. The modern Pagan version of Druidry prevalent in the BDO and other groups began to take shape with the formation of the Order of Bards, Ovates and Druids by Ross Nichols in 1964, although Nichols himself was a Christian.
The BDO seeks to bring modern Druidry closer to our perception of the essentially shamanic nature of the Druidry of our ancestors. We therefore characterise Druidry as a native spirituality of Europe and people of European origin (though open to all), equivalent to the traditions of Native Americans, Australian Aboriginals and other tribal belief systems around the world, while it also shares many commonalities with Hinduism and with ancient Greek paganism.
Incidentally, the Welsh Gorsedd of Bards, founded by Iolo Morganwg in 1792, bears no relationship whatsoever to modern pagan Druidry. It is a cultural organisation, awarding membership to people deemed to have made significant contributions to Welsh culture. Inasmuch as there is any religious content to its gatherings, it consists of singing Christian hymns. That's why the Archbishop of Canterbury, Rowan Williams (left) is happy to be a member, while the Queen is an honorary member. Neither of them are pagans, despite what you might read on some American evangelical websites. The Archbishop is, however, an Incredible String Band fan.