HOW DID POLYBIUS PERFECT CLEOXENUS AND DEMOCLEITUS SIGNALLING METHOD, 2200 YEARS AGO ?

We propose an answer to the question of how Polybius perfected Cleoxenus and Democleitus « most recent method » of signalling letters in the first digital optical telegraph. We show that the Polybius’ choice of subdividing the 24 letters of the Greek alphabet in five tablets minimises the number of torches necessary to operate the signalling system, that he describes in the short technical text (his “paper”) inserted in The Histories [x, 43-47]. This Polybius’ particular choice cannot be a coincidence, and the fine details of the equipment that he describes, an engineered system, make us confident that our conjecture may be well grounded. As moderns, we can apply statistical analysis and information theory, by knowing the relative frequencies of the (Modern) Greek alphabet. We have found that Polybius’ choice is optimum also according to probability theory because it minimises the average number of torches.