Philo Judaeus Legatio Ad Gaium 30

[30] It is said moreover, that this youth, being ordered to slay himself with his own hands, while a centurion and a captain of a thousand were standing by (who had been expressly commanded to take no part in the horrid deed, since it was not lawful for the descendants of the emperors to be put to death by any one else; for Caius remembered the laws amid his lawless acts, and had some regard for piety in all his impious deeds, imitating as well as he could the nature of truth); he, not knowing how to kill himself, for he had never seen any one else put to death, and had never had any practise in fighting with weapons, which is the usual exercise and course of instruction for children who are being educated with a view to become leaders and rulers, on account of the wars which they may have to conduct, at first exhorted those officers who had come to him to put him to death themselves, stretching out his neck;