Gallic Wars

G. Julius Caesar, Commentarii de Bello Galileo English translations by, among others, S. A. Handford ( The Conquest of Gaul ) and K. Gilliver ( Caesar s Gallic Wars, 58-50 BC ) see also online synopses. 

The most common type of cipher in ancient times was the substitution cipher. This was the type of cipher employed by Julius Caesar during the Gallic Wars, by the Italian Leon Battista Alberti in a device called the Alberti Cipher Disk described in a treatise in 1467, and by Sir Francis Bacon of Great Britain. In the 1400 s, the Egyptians discovered a way to decrypt substitution ciphers by analyzing the frequency of the letters of the alphabet. Knowing the frequency of a letter made it easy to decipher a message. 

Codes and ciphers have been used since the beginning of recorded time, when humans drew figures on a cave wall to communicate ideas. During the Gallic Wars, Julius Caesar devised one of the first substitution ciphers by printing the ciphertext alphabet with the letters moved four places to the left under the plaintext alphabet. 

Caesar, The Gallic Wars, Book IV, 17 The greater the force and thrust of the water, the tighter were the balks held in lock. He seems to have had a structural action explained to him and to have only partially understood. The timber pairings above and below each crutch, which would be necessary for a scissor effect to tighten the assembly under lateral pressure, are not mentioned, contrary to so many other clear descriptions. 

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