The vague idea that the Druids were philosophers was repeated parrot-like by writer after writer, who regarded barbaric races as Rousseau and his school looked upon the "noble savage." Roman writers, sceptical of a future life, were fascinated by the idea of a barbaric priesthood teaching the doctrine of immortality in the wilds of Gaul. For this teaching the poet Lucan sang their praises. The Druids probably first impressed Greek and Latin observers by their magic, their organisation, and the fact that, like many barbaric priesthoods, but unlike those of Greece and Rome, they taught certain doctrines. Their knowledge was divinely conveyed to them; "they speak the language of the gods;"978 hence it was easy to read anything into this teaching. Thus the Druidic legend rapidly grew. On the other hand, modern writers have perhaps exaggerated the force of the classical evidence. When we read of Druidic associations we need not regard these as higher than the organised priesthoods of barbarians. Their doctrine of metempsychosis, if it was really taught, involved no ethical content as in Pythagoreanism. Their astronomy was probably astrological979; their knowledge of nature a series of cosmogonic myths and speculations. If a true Druidic philosophy and science had existed, it is strange that it is always mentioned vaguely and that it exerted no influence upon the thought of the time.
Classical sentiment also found a connection between the Druidic and Pythagorean systems, the Druids being regarded as conforming to the doctrines and rules of the Greek philosopher.980 It is not improbable that some Pythagorean doctrines may have reached Gaul, but when we examine the point at which the two systems were supposed to meet, namely, the doctrine of metempsychosis and immortality, upon which the whole idea of this relationship was founded, there is no real resemblance. There are Celtic myths regarding the rebirth of gods and heroes, but the eschatological teaching was apparently this, that the soul was clothed with a body in the other-world. There was no doctrine of a series of rebirths on this earth as a punishment for sin. The Druidic teaching of a bodily immortality was mistakenly assumed to be the same as the Pythagorean doctrine of the soul reincarnated in body after body. Other points of resemblance were then discovered. The organisation of the Druids was assumed by Ammianus to be a kind of corporate life—sodaliciis adstricti consortiis—while the Druidic mind was always searching into lofty things,981 but those who wrote most fully of the Druids knew nothing of this.
The Druids, like the priests of all religions, doubtless sought after such knowledge as was open to them, but this does not imply that they possessed a recondite philosophy or a secret theology. They were governed by the ideas current among all barbaric communities, and they were at once priests, magicians, doctors, and teachers. They would not allow their sacred hymns to be written down, but taught them in secret,982 as is usual wherever the success of hymn or prayer depends upon the right use of the words and the secrecy observed in imparting them to others. Their ritual, as far as is known to us, differs but little from that of other barbarian folk, and it included human sacrifice and divination with the victim's body. They excluded the guilty from a share in the cult—the usual punishment meted out to the tabu-breaker in all primitive societies.
The idea that the Druids taught a secret doctrine—monotheism, pantheism, or the like—is unsupported by evidence. Doubtless they communicated secrets to the initiated, as is done in barbaric mysteries everywhere, but these secrets consist of magic and mythic formulæ, the exhibition of Sacra, and some teaching about the gods or about moral duties. These are kept secret, not because they are abstract doctrines, but because they would lose their value and because the gods would be angry if they were made too common. If the Druids taught religious and moral matters secretly, these were probably no more than an extension of the threefold maxim inculcated by them according to Diogenes Laertius: "To worship the gods, to do no evil, and to exercise courage."983 To this would be added cosmogonic myths and speculations, and magic and religious formulæ. This will become more evident as we examine the position and power of the Druids.
In Gaul, and to some extent in Ireland, the Druids formed a priestly corporation—a fact which helped classical observers to suppose that they lived together like the Pythagorean communities. While the words of Ammianus—sodaliciis adstricti consortiis—may imply no more than some kind of priestly organisation, M. Bertrand founds on them a theory that the Druids were a kind of monks living a community life, and that Irish monasticism was a transformation of this system.984 This is purely imaginative. Irish Druids had wives and children, and the Druid Diviciacus was a family man, while Cæsar says not a word of community life among the Druids. The hostility of Christianity to the Druids would have prevented any copying of their system, and Irish monasticism was modelled on that of the Continent. Druidic organisation probably denoted no more than that the Druids were bound by certain ties, that they were graded in different ranks or according to their functions, and that they practised a series of common cults. In Gaul one chief Druid had authority over the others, the position being an elective one.985 The insular Druids may have been similarly organised, since we hear of a chief Druid, primus magus, while the Filid had an Ard-file, or chief, elected to his office.986 The priesthood was not a caste, but was open to those who showed aptitude for it. There was a long novitiate, extending even to twenty years, just as, in Ireland, the novitiate of the File lasted from seven to twelve years.987
The Druids of Gaul assembled annually in a central spot, and there settled disputes, because they were regarded as the most just of men.988 Individual Druids also decided disputes or sat as judges in cases of murder. How far it was obligatory to bring causes before them is unknown, but those who did not submit to a decision were interdicted from the sacrifices, and all shunned them. In other words, they were tabued. A magico-religious sanction thus enforced the judgments of the Druids. In Galatia the twelve tetrarchs had a council of three hundred men, and met in a place called Drunemeton to try cases of murder.989 Whether it is philologically permissible to connect Dru- with the corresponding syllable in "Druid" or not, the likeness to the Gaulish assembly at a "consecrated place," perhaps a grove (nemeton), is obvious. We do not know that Irish Druids were judges, but the Filid exercised judgments, and this may be a relic of their connection with the Druids.990
Diodorus describes the Druids exhorting combatants to peace, and taming them like wild beasts by enchantment.991