Res Gestae

As soon as he had refreshed his body, which was inured to toil, by a brief rest in sleep, he awoke and in person attended to the changing of the guards and pickets, and after these serious duties took refuge in the pursuit of learning.

And if the nightly lamps amid which he worked could have given oral testimony, they would certainly have borne witness that there was a great difference between him and some other princes, since they knew that he did not indulge in pleasure, even to the extent which nature demanded.