Amongst the Romans, the custody and interpretation of the laws continued solely in the college of the pontiffs for above a century.[7] The time in which the Druid priesthood was instituted is unknown.

It probably rose, like other institutions of that kind, from low and obscure beginnings, and acquired from time, and the labors of able men, a form by which it extended itself so far, and attained at length so mighty an influence over the minds of a fierce and otherwise ungovernable people.

Of the place where it arose there is somewhat less doubt: Caesar mentions it as the common opinion that this institution began in Britain, that there it always remained in the highest perfection, and that from thence it diffused itself into Gaul.

I own I find it not easy to assign any tolerable cause why an order of so much authority and a discipline so exact should have passed from the more barbarous people to the more civilized, from the younger to the older, from the colony to the mother country: but it is not wonderful that the early extinction of this order, and that general contempt in which the Romans held all the barbarous nations, should have left these matters obscure and full of difficulty.
The Druids were kept entirely distinct from the body of the people; and they were exempted from all the inferior and burdensome offices of society, that they might be at leisure to attend the important duties of their own charge.

They were chosen out of the best families, and from the young men of the most promising talents: a regulation which placed and preserved them in a respectable light with the world.