In his autobiography Confessions, written at the end of the 4th century AD, St Augustine of Hippo writes how utterly stunned he was when he observed Bishop Ambrose of Milan reading a book. Ambrose’s mouth was closed, his lips didn’t move. It was a miracle!
In those days readers habitually moved their fingers, slowly, along the lines, pronouncing aloud every word. It took humankind another 500 years to develop silent reading ability to the level that it became a norm.