Julius Caesar is recorded as having routinely used ciphers, and evidence of secret writing and coded messages dates back further to the ancient civilizations of China, India and Greece. This illustrated history explains the development of setting and cracking codes from simple substitution ciphers in use in medieval Europe to the decoding of the incendiary Zimmerman telegram in 1917, Alan Turings breakthrough in mechanized analysis at Bletchley Park and modern computer-generated systems of encryption and decryption.