In reply to:
But could Caesar read to himself without moving his lips?
I don't have the reference about Caesar to hand to quote exactly, but some 400 years later, here is Augustine's comment on Ambrose, bishop of Milan (translated by Henry Chadwick):
When he was reading, his eyes ran over the page and his heart perceived the sense, but his voice and tongue were silent. He did not restrict access to anyone coming in, nor was it customary even for a visitor to be announced. Very often when we were there, we saw him silently reading and never otherwise. After sitting for a long time in silence (for who would dare to burden him in such intent concentration?) we used to go away. We supposed that in the brief time he could find for his mind's refreshment, free from the hubbub of other people's troubles, he would not want to be invited to consider another problem. We wondered if he read silently perhaps to protect himself in case he had a hearer interested and intent on the matter, to whom he might have to expound the text being read if it contained difficulties, or who might wish to debate some difficult questions. If his time were used up in that way, he would get through fewer books than he wished. Besides, the need to preserve his voice, which used easily to become hoarse, could have been a very fair reason for silent reading. Whatever motive he had for his habit, this man had a good reason for what he did.
Chadwick has footnote that "In antiquity, silent reading was uncommon, not unknown."
Bingley
