Aesop's Fables have handed down a symbolic code: "The hieroglyphic writing of ancient Egypt and of Mexico seem to have been, in some detree, a popularized or exoteric outgrowth of a secret language.  ... A symbol-code was sometimes used by Plato and other Greek philosophers, in relation to Pythagorean and Orphic lore; ... throughout the Celtic world the Druids conveyed all their esoteric teachings symbolically; ... the use of parables, as in the sermons of Jesus and of the Buddha, and of other Great Teachers, illustrated the same tendency; ... through works like Aesop's Fables, and the miracle and mystery plays of medieval Europe, many of the old Oriental symbols have been introduced into the modern literatures of the West" (the introduction to The Tibetan Book of the Dead).

From The Fables of Aesop, 1925.