In Celtic polytheism the word Druid denotes the priestly class in ancient Celtic societies, which existed through much of Western Europe north of the Alps and in the British Isles. Druidic practices were part of the culture of all the tribal peoples called "Keltoi" and "Galatai" by Greeks and "Celtae" and "Galli" by Romans, which evolved into modern English "Celtic" and "Gaulish".
Modern attempts at reconstructing or reinventing Druidism are called Neo-druidism.
The word Druid (reconstructed as *druwis or *druwids in Old Celtic) is probably derived from Indo-European roots meaning "oak/strong" and "knowledge," although some believe that it may be pre-Indo-European. By Ancient Greek writers, the earliest to discuss the Celts, the word is spelled Δρυίδης (Druides), and was associated with δρυς (drus "oak tree"). It appears in Old Irish as druí, giving draoi (magician) in Modern Irish and druidh (enchanter) and draoidh (magician) in Scottish Gaelic. The Old Irish druídecht gives Modern Irish draoiocht (magic). Welsh dryw (seer) may be cognate.
From what little we know of late Druidic practice, it appears deeply traditional and conservative, in the sense that Druids were conserving repositories of culture and lore. It is impossible now to judge whether this continuity had deep historical roots and originated in the social transformations of the late La Tène culture, or whether there had been a discontinuity and a Druidic religious innovation.
Our historical knowledge of Druids is very limited. Druidic lore consisted of a large number of verses learned by heart and it has been claimed that twenty years were required to complete the course of study. There may have been a Druidic teaching center on Anglesey (Ynys Môn) centred on magical lakes, but what was taught there, or at other centers, is conjecture. Of the Druids' oral literature (sacred songs, formulas for prayers and incantations, rules of divination and magic) not one verse has survived, even in translation, nor is there even a legend that can be called purely Druidic, without a Roman and/or Christian overlay or interpretation.
Caesar's Commentarii de Bello Gallico gives the fullest account of the Druids. Caesar notes that all men of any rank and dignity in Gaul were included either among the Druids or among the nobles, indicating that they formed two classes. The Druids constituted the learned priestly class, and as guardians of the unwritten ancient customary law they had the power of executing judgments, among which exclusion from society was the most dreaded. Druids were not a hereditary caste, though they enjoyed exemption from military service as well as from payment of taxes. The course of training to which a novice had to submit was protracted.
All instruction was communicated orally, but for ordinary purposes, Caesar reports that the Gauls had a written language in which they used Greek characters. In this he probably draws on earler writers; by the time of Caesar, Gaulish had moved from the Greek script to the Latin script.
As a result of this prohibition — and of the decline of Gaulish in favour of Latin — no druidic documents, if there ever were any, have survived. "The principal point of their doctrine", says Caesar, "is that the soul does not die and that after death it passes from one body into another" (see metempsychosis). This observation led several ancient writers to the unlikely conclusion that the Druids may have been influenced by the teachings of the Greek philosopher Pythagoras. Caesar also notes the druidic sense of the guardian spirit of the tribe, whom he translated as Dispater, with a general sense of Father Hades. However, linguistically Dis Pater is related to Jupiter (Jovis Pater), from Indo-European word Dyeus.
Writers such as Diodorus and Strabo, with less firsthand experience than Caesar, were of the opinion that the Celtic priestly order or class included Druids, Bards and Vates (soothsayers).
Pomponius Mela is the first author who says that the Druids' instruction was secret, and was carried on in caves and forests. Certain groves within forests were sacred, and the Romans and Christians alike cut them down and burned the wood. Human sacrifice has sometimes been attributed to Druidism. While this may be Roman propaganda, human sacrifice was an old European inheritance and the Gauls may have offered human sacrifices, whether of criminals or, to judge from Roman reports, of war captives.
It was also claimed by Roman writers that a general assembly of the order was held once every year within the territories of the Carnutes in Gaul.
Cicero remarks on the existence among the Gauls of augurs or soothsayers, known by the name of Druids; he had made the acquaintance of one Divitiacus, an Aeduan. Diodorus asserts, on unnamed sources, that a sacrifice acceptable to the Celtic gods had to be attended by a Druid, for they were the intermediaries. He also claims that before a battle they often threw themselves between two armies to bring about peace.
Druids were seen as essentially non-Roman: a prescript of Augustus forbade Roman citizens to practise Druidical rites. In Strabo we find the Druids still acting as arbiters in public and private matters, but they no longer dealt with cases of murder. Under Tiberius the Druids were suppressed by a decree of the Senate, but this had to be renewed by Claudius in 54 CE. In Pliny their activity is limited to the practice of medicine and sorcery. According to him, the Druids held the mistletoe in the highest veneration and groves of oak were their chosen retreats. In what is probably a fanciful extension of this story, Pliny claims that the mistletoe was cut with a golden knife by a priest clad in a white robe, two white bulls being sacrificed on the spot.
Tacitus, in describing the attack made on the island of Mona (Anglesey or Ynys Môn in Welsh) by the Romans under Suetonius Paulinus, represents the legionaries as being awestruck on landing by the appearance of a band of Druids, who, with hands uplifted to the sky, poured forth terrible imprecations on the heads of the invaders. The courage of the Romans, however, soon overcame such fears, according to the Roman historian; the Britons were put to flight, and the sacred groves of Mona were cut down.
After the 1st century CE the continental Druids disappeared entirely and were referred to only on very rare occasions. Ausonius, for one instance, apostrophizes the rhetorician Attius Patera as sprung from a race of Druids.
Early Druids in Britain and Ireland
The story of Vortigern as reported by Nennius provides one of the very few glimpses of Druidic survival in Britain after the Roman conquest: unfortunately, Nennius is noted for mixing fact and legend in such a way that it is now impossible to know the truth behind his text. For what it is worth, he asserts that, after being excommunicated by Germanus, the British leader Vortigern invited twelve Druids to assist him.
Social and religious influence
The Druids' influence was as much social as religious. They not only performed roles similar to modern priests, but were often the philosophers, scientists, lore-masters, teachers, judges and counsellors to the kings. The Druids linked the Celtic peoples with their numerous gods, the lunar calendar and the sacred natural order. They were suppressed in Gaul and Britain after the Roman conquests, but retained their influence in Ireland until the coming of Christianity. The Druids' roles were then assumed by the bishop and the abbot, who were usually not the same individual, however, and might find themselves in direct competition.
Nevertheless, much traditional rural religious practice can still be discerned from Christian interpretations and survives in practices like Halloween observances, corn dollies and other harvest rituals, the myths of Puck, woodwoses, "lucky" and "unlucky" plants and animals and the like. Orally-transmitted material may have exaggerated deep origins in antiquity, however, and is constantly subject to influence from surrounding culture.
The Druidic Revival
In the 18th century, England and Wales experienced a revival of interest in the Druids, inspired by the antiquaries John Aubrey, John Toland and William Stukeley. The poet William Blake was involved in the revival and may have been an Archdruid; the Ancient Druid Order, which existed from 1717 until it split into two groups in 1964, never used the title "Archdruid" for any member but credited Blake as having been its Chosen Chief from 1799 to 1827.
John Aubrey was the first modern writer to connect Stonehenge and other megalithic monuments with Druidry, a misconception that shaped ideas of Druidry during much of the 19th century. Some modern Druidry enthusiasts claim Aubrey was an archdruid in possession of an uninterrupted tradition of Druidic knowledge, even though Aubrey, an uninhibited collector of lore and gossip, never entered a corroborating word in his voluminous surviving notebooks. John Toland was fascinated by Aubrey's Stonehenge theories, and wrote his own book about the monument without crediting Aubrey. Toland founded the Ancient Druid Order in London in 1717; interestingly enough, modern Freemasonry was founded in the same year and the same location, Covent Garden's Apple Tree Tavern.
Druids began to figure widely in popular culture with the first advent of Romanticism. Chateaubriand's novel Les Martyrs (1809) narrated the doomed love of a Druid priestess and a Roman soldier; though Chateaubriand's theme was the triumph of Christianity over pagan Druids, the setting was to continue to bear fruit. Opera provides a barometer of well-informed popular European culture in the early 19th century: in 1817 Giovanni Pacini brought Druids to the stage in Trieste with an opera to a libretto by Felice Romani about a Druid priestess, La Sacerdotessa d'Irminsul ("The Priestess of Irminsul"). The most famous Druidic opera, Bellini's Norma was a fiasco at La Scala, when it premiered the day after Christmas, 1831, but in 1833 it was a hit in London. For its libretto Felice Romani reused some of the pseudo-Druidical background of La Sacerdotessa to provide color to a standard theatrical conflict of love and duty that was related to Medea, as it had recently been recast for a popular Parisian play by Alexandre Soumet: the diva of Norma's hit aria, "Casta Diva", is the moon goddess, being worshipped in the "grove of the Irmin statue".
In the 19th, some dubious figures arose with outlandish claims and forged documents they claimed were historical. A central figure in this Druidic reinvention, inspired by Henry Hurle, is Edward Williams, better known as Iolo Morganwg. His writings, published posthumously as The Iolo Manuscripts (1848) and Barddas (1862), are not considered credible by contemporary Druidic movements because it has become impossible to distinguish Williams' inventions from the genuine material. Williams claimed to have collected ancient knowledge in a "Gorsedd of Bards of the Isles of Britain" he had organized. Many scholars deem part or all of Williams's work to be fabrication, and purportedly many of the documents are of his own fabrication, but a large portion of the work has indeed been collected from meso-pagan sources dating from as far back as 600 A.D. Regardless, it has become impossible to seperate the original source material from the fabricated work, and the documents are considered irrelevant by most serious scholars.
An unfortunate result of the reinvention, which took place, ironically, just as modern archaeological and historical methods were being developed, is that it has shaped public perceptions of historical Druidry and continues to shape some modern forms of it. The British Museum website is suitably blunt:
"Modern Druids have no direct connection to the Druids of the Iron Age. Many of our popular ideas about the Druids are based on the misunderstandings and misconceptions of scholars 200 years ago. These ideas have been superseded by later study and discoveries".