Suetonius Divus Augustus 38

He was unsparing in the reward of military merit, having granted to above thirty generals the honour of the greater triumph; besides which, he took care to have triumphal decorations voted by the senate for more than that number. That the sons of senators might become early acquainted with the administration of affairs, he permitted them, at the age when they took the garb of manhood, ¹ to assume also the distinction of the senatorian robe, with its broad border, and to be present at the debates in the senate-house. When they entered the military service, he not only gave them the rank of military tribunes in the legions, but likewise the command of the auxiliary horse. And that all might have an opportunity of acquiring military experience, he commonly joined two sons of senators in command of each troop of horse. He frequently reviewed the troops of the equestrian order, reviving the ancient custom of a cavalcade, ² which had been long laid aside. But he did not suffer any one to be obliged by an accuser to dismount while he passed in review, as had formerly been the practice. As for such as were infirm with age, or any way deformed, he allowed them to send their horses before them, coming on foot to answer to their names, when the muster roll was called over soon afterwards. He permitted those who had attained the age of thirty-five years, and desired not to keep their horse any longer, to have the privilege of giving it up.