Plutarch of Chaeronea (c. 46 B.C.-c. A.D.100) recounts a humorous anecdote regarding Julius Caesar reading silently.
The story is told, that when the great question of the conspiracy of Catiline, which had like to have been the destruction of the commonwealth, was debated in the senate, Cato the Younger and Julius Caesar were both standing up, contending together on the decision to be come to; at which time a little note was delivered to Caesar from without, which he took and read silently to himself. Upon this, Cato cried out aloud, and accused Caesar of holding correspondence with and receiving letters from the enemies of the commonwealth; and when many other senators exclaimed against it, Caesar delivered the note as he had received it to Cato, who reading it found it to be a love-letter from his own sister Servilia, and threw it back again to Caesar with the words, "Keep it, you drunkard," and returned to the subject of the debate.
In his Confessions St. Augustine (A.D.354-430) remarks on Bishop Ambrose's habit of reading silently without moving his lips, rather than aloud for the edification of his listeners.
But when he was reading, his eye glided over the pages, and his heart searched out the sense, but his voice and tongue were at rest. Ofttimes when we had come...we saw him thus reading to himself, and never otherwise; and having long sat silent...we were fain to depart, conjecturing that in the small interval which he obtained, free from the din of others' business, for the recruiting of his mind, he was loth to be taken off; and perchance he dreaded lest if the author he read should deliver any thing obscurely, some attentive or perplexed hearer should desire him to expound it, or to discuss some of the harder questions; so that his time being thus spent, he could not turn over so many volumes as he desired; although the preserving of his voice (which a very little speaking would weaken) might be the truer reason for his reading to himself. But with what intent soever he did it, certainly in such a man it was good.
In his Rule St. Benedict (A.D.480-547) prescribes a time of silent rest for the monks after the mid-day meal, during which a monk may read but only if he does so silently, which suggests that silent reading was still something that needed to be specified, as opposed to the more common reading aloud.
...when they have risen from table, let them rest in their beds in complete silence; or if, perhaps, anyone desireth to read for himself, let him so read that he doth not disturb others.