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Curiosities of Cypher Now this is a specimen of the safest of all secret communications, but it can only be resorted to on certain rare occasions. When a lengthy despatch is required to be forwarded, and when such means as those given above are out of the question, some other method must be employed. Herodotus gives us a story to the point: it is found also, with variations, in Aulus Gellius.

"Histiæus, when he was anxious to give Aristagoras orders to revolt, could find but one safe way, as the roads were guarded, of making his wishes known: which was by taking the trustiest of his slaves, shaving all the hair from off his head, and then pricking letters upon the skin, and waiting till the hair grew again. This accordingly he did; and as soon as ever the hair was grown, he despatched the man to Miletus, giving him no other message than this: 'When thou art come to Miletus, bid Aristagoras shave thy head, and look thereon.' Now the marks on the head were a command to revolt."—Bk. v. 35.

In this case no cypher was employed; we shall come, now, to the use of cyphers.

When a despatch or communication runs great risk of falling into the hands of an enemy, it is necessary that its contents should be so veiled, that the possession of the document may afford him no information whatever. Julius Caesar and Augustus used cyphers, but they were of the utmost simplicity, as they consisted merely in placing D in the place 19