de bello gallico, 6.18

The Gauls proclaim that they all are descended from the god Dis, and say that this has been handed down by the Druids. Because of this reason they make the divisions of every season not by the number of days but of nights; they observe birthdays and the beginnings of months and years thus that the day follows the night. Among the other customs of life, they differ in this from nearly (all) remaining, that they do not permit their children to approach them openly unless when they have grown up so as to be able to bear the duty of war; and they consider it as shameful for a son of boyish age to stand in public in the sight of his father.