The origin of reading can be traced back to the invention of writing (through the 4th millenium BC). But it surprises some that reading silently was not always common. Reading silently is such a new concept that the earliest known mention of silent reading comes from St. Augustine’s Confessions in 398 AD.
St. Augustine speaks about St. Ambrose in his book. He specifically mentions the oddity of St. Ambrose’ reading methods:
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.
St. Ambrose was reading silently, and this was strange for the time. We can see just how strange it really was when in the next passage it is described that many would intentionally watch him:
Oftentimes when we had come (for no man was forbidden to enter, nor was it his wont that any who came should be announced to him), we saw him thus reading to himself, and never otherwise
Although the reason for his silent reading is unknown, St. Augustine believed that “…with what intent soever he did it, certainly in such a man it was good.”