Silent Reading Is Sort of a New Thing

At least it was novel enough for Augustine of Hippo (354 - 430) to remark upon it in his autobiographical Confessions. He's what he said of St. Ambrose:

Now, as he read, his eyes glanced over the pages and his heart searched out the sense, but his voice and tongue were silent. Often when we came to his room--for no one was forbidden to enter, nor was it his custom that the arrival of visitors should be announced to him--we would see him thus reading to himself. After we had sat for a long time in silence--for who would dare interrupt one so intent?--we would then depart, realizing that he was unwilling to be distracted in the little time he could gain for the recruiting of his mind, free from the clamor of other men's business. Perhaps he was fearful lest, if the author he was studying should express himself vaguely, some doubtful and attentive hearer would ask him to expound it or discuss some of the more abstruse questions, so that he could not get over as much material as he wished, if his time was occupied with others. And even a truer reason for his reading to himself might have been the care for preserving his voice, which was very easily weakened. Whatever his motive was in so doing, it was doubtless, in such a man, a good one.