word _drus_, an
oak, has been questioned by such a competent Celtic scholar as M.
d'Arbois de Jubainville, but on this point it cannot be said that his
criticism is conclusive. The writers of the ancient world who refer to
the Druids, do not always make it sufficiently clear in what districts
the rites, ceremonies, and functions which they were describing
prevailed. Nor was it so much the priestly character of the Druids that
produced the deepest impression on the ancients. To some philosophical
and theological writers of antiquity their doctrines and their apparent
affinities with Pythagoreanism were of much greater interest than their
ceremonial or other functions. One thing at any rate is clear, that the
Druids and their doctrines, or supposed doctrines, had made a deep
impression on the writers of the ancient world. There is a reference to
them in a fragment of Aristotle (which may not, however, be genuine) that
is of interest as assigning them a place in express terms both among the
Celts and the Galatae. The prominent feature of their teaching which had
attracted the attention of other writers, such as the historian Diodorus
Siculus and the Christian theologian Clement of Alexandria, was the
resemblance of their doctrine concerning the immortality and
transmigration of the soul to the views of Pythagoras. Ancient writers,
however, did not always remember that a religious or philosophical
doctrine must not be treated as a thing apart, but must be interpreted in
its whole context in relation to its development in history and in the
social life of the community in which it has flourished. To some of the
ancients the superficial resemblance between the Druidic doctrine of the
soul's future and the teaching attributed to Pythagoras was the essential
point, and this was enough to give the Druids a reputation for
philosophy, so that a writer like Clement of Alexandria goes so far as to
regard the Druids of the 'Galatae' along with the prophets of the
Egyptians, the 'Chaldaeans' of the Assyrians, the 'philosophers of the
Celts,' and the Magi of the Persians as the pioneers of philosophy among
the barbarians before it spread to the Greeks. The reason for the
distinction drawn in this passage between the 'Druids of the Galatae' and
'the philosophers of the Celts' is not clear. Diodorus Siculus calls
attention to the Druidic doctrine that the souls of men were immortal,
and that after the lapse of an appointed number