Priests of the god or gods identified with the oak
Druidism. The etymology of this word from the Greek drus, "oak", has been a favorite one since the time of Pliny the Elder; according to this the druids would be the priests of the god or gods identified with the oak. It is true that the oak plays an important part as the sacred tree in the ancient cult of the Aryans of Europe, and this etymology is helped out by the Welsh word for druid, viz. derwydd. But there is a difficulty in equating the synonymous Irish draoi and Welsh derwydd. Probably the best-substantiated derivation of the word is from the root vid, "to know", and the intensive prefix dru. According to this etymology, the druids would be the "very wise and learned ones". But this, like the others, is merely a conjecture, and it has been surmised that the word as well as the institution was not of Celtic origin. Although the druids are mentioned with more or less fullness of account by a score of ancient writers, the information to be derived from their statements is very meagre, and very little of it is at first hand. Even Caesar, who probably came more in contact with the druids than any other writer, does not seem to speak of the druids of his time in particular, but of the druids in general. With the ancient writers the word druid had two meanings: in the stricter sense it meant the teachers of moral philosophy and science; in the wider sense it included the priests, diviners, judges, teachers, physicians, astronomers, and philosophers of Gaul. They formed a class apart and kept the people, who were far inferior to them in culture, in subjection. They were regarded as the most just of men, and disputes both public and private were referred to them for settlement. Thus their influence was much more a social than a religious one, in spite of the common opinion that they were exclusively a priestly class or Gaulish clergy. They enjoyed certain privileges, such as exemption from military service and the payment of taxes; and the ancient authors are unanimous in speaking of the great honors which were shown them.
Above all, the druids were the educators of the nobility. Their instruction was very varied and extensive. It consisted of a large number of verses learned by heart, and we are told that sometimes twenty years were required to complete their course of study. They held that their learning should not be consigned to writing. They must have had a considerable oral literature of sacred songs, formulae of prayers, rules of divination and magic, but of all this lore not a verse has come down to us, either in their own language or in the form of translation, nor is there even a legend that we can call with certain druidic. Pomponius Mela if the first author who says that their instruction was secret and carried on in caves and forests. It is commonly believed that the druids were the stubborn champions of Gaulish liberty and that they took a direct part in the government, of the nation, but this is an hypothesis which, however probable, is not supported, for the early period at least, by any text or by the statement of any ancient author. "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." But, as is well known, the belief in the immortality of the soul was not peculiar to the teachings of the philosophers of Gaul. Just what was the nature of that second life in which they believed is not quite clear. Some of the Greek authors, struck by the analogy of this doctrine with that of Pythagoras, believed that the druids had borrowed it from the Greek philosopher or from one of his disciples. The practice of human sacrifice, which has often been imputed to the druids, is now known to have been a survival of a pre-druidic custom, although some members of the druidic corporation not only took part in, but preseded at, these ceremonies. Nor has it been proved that the druids had gods of their own or had introduced any new divinity or rites into Gaul, with the exception perhaps of the Dispater, who, according to Caesar, was regarded by the druids as the head of the nation, and who may have owned his origin to their belief. The druids, in addition to teaching, which was their most important occupation, seem to have been content to preside over the traditional religious ceremonies and to have acted as intermediaries between the gods, such as they found them, and men. It is certain that they had a philosophy, but it is very unlikely that their doctrines had penetrated into the great mass of the population.
Although the only positive information we possess on the druids is to the effect that their institution existed in Gaul and Britain between the years 53 B.C. and A.D. 77, there is evidence to show that it must have existed from a much earlier time and lasted longer than the limits fixed by these dates. It seems reasonable to suppose that the influence of the druids was already at its decline when Caesar made his campaigns in Gaul, and that to them was due the civilization of Gaul in the fifth and fourth centuries B.C. We may affirm that references to the druids and signs of the existence of their institution, in the germ at least, are found which would date them as early as the third century B.C. With the Roman conquest of Gaul the druids lost all their jurisdiction, druidism suffered a great decay, and there is no reason to believe that it survived long after A.D. 77, the date of the last mention of the druids as still in existence. The opening of the schools of Marseilles, Bordeaux, and Lyons put an end to their usefulness as teachers of moral philosophy; and if some of them remained scattered here and there in Gaul, most of them were obliged to emigrate to Britain. The Emperors Tiberius and Claudius abolished certain practices in the cult of the druids, their organization, and their assemblies, but their disappearance was gradual and due as much to the romanization of the land as to any political measure or act of violence or persecution on the part of Rome. Yet there can be no doubt that Rome feared the druids as teachers of the Gallo-Roman youth and judges of trials. In Gaul in the third century of the Christian Era there is mention of women who predicted the future and were known as druidesses, but they were merely sorcerers, and we are not to conclude from the name they bore that druidism was still in existence at that late date. According to Caesar, it was a tradition in Gaul in his time that the druids were of British origin and that it was to Great Britain that they went to make a thorough study of their doctrine, but the authors of antiquity throw very little light on the institution and practices of druidism in the island of Britain.
Our information concerning the druids of Ireland is drawn from what the Christian hagiographers have written of them and what can be gathered from the casual references to them in the epic literature of Ireland. We have only fragmentary notices of the matter of their teachings, but it is clear that there were the most striking resemblances between the druids of Ireland and those of Gaul. In both lands they appear as magicians, diviners, physicians, and teachers, and not as the representatives of a certain religion. In the saga tales of Ireland they are most often found in the service of kings, who employed them as advisers because of their power in magic. In the exercise of this they made use of wands of yew, upon which they wrote in a secret character called ogham. This was called their "keys of wisdom". In Ireland, as in Gaul, they enjoyed a high reputation for learning, and some Irish druids held a rank even higher than that of the king. But they were not exempt from military service nor do they seem to have formed a corporation as in Gaul. In the earliest Christian literature of Ireland the druids are represented as the bitterest opponents of Christianity, but even the Christians of the time seem to have believed in their supernatural power of prophecy and magic. The principal thesis in M. Alexandre Bertrand's book on the religion of the Gauls is that druidism was not an isolated institution in antiquity, without analogy but that its parallel is to be looked for in the lamaseries which still survive in Tatary and Tibet. He maintains that great druidic communities flourished in Gaul, Britain, and Ireland many centuries before the Christian Era, and that these were the models and beginnings of the abbeys of the Western monks. In this way he would explain the literary and scientific superiority of the monasteries of Ireland and Wales in the early Middle Ages. However ingenious and attractive this hypothesis may be, it is not supported by any historical documents, and many negative arguments might be brought to bear against it.