He goes on to explain:
Once there was an ancient Egyptian god called Theuth. He invented numbers, geometry, astronomy, dice, and writing. One day Theuth went to see Thamus, the King of Upper Egypt, and began to show him all he had invented. When Theuth reached the alphabet, he explained: “This is an invention which will greatly improve the wisdom and memory of your people.” But the king replied: “O ingenious Theuth, your alphabet will have exactly the opposite effect from the one you claim. As soon as Egyptians begin to rely upon written wisdom, they will stop using their memory and call things to mind not by using their own internal resources, as they should, but by using these external signs.”
– Plato, Phaedo, 274, 275