Previously, fire-signalling was useful only for expected, predetermined messages, with no way to convey novel messages about unexpected events. In his Histories, Polybius outlines the need for effective signalling in warfare, leading to the development of the square.
For example, the key phrase " polybius cipher" would lead to the reordered square below.Īpplications Telegraphy ĭiagram of a fire signal using the Polybius cipher Alternatively, a 6 × 6 grid may be used to allow numerals or special characters to be included as well as letters.Ī 6 × 6 grid is also usually used for the Cyrillic alphabet (the most common variant has 33 letters, but some have up to 37) or Japanese hiragana (see cryptography in Japan).Ī key could be used to reorder the alphabet in the square, with the letters (without duplicates) of the key being placed at the beginning and the remaining letters following it in alphabetical order. The 26 letters of the Latin/English alphabet do not fit in a 5 × 5 square, two letters must be combined (usually I and J as above, though C and K is an alternative). With the modern Latin alphabet, this is the typical form:Įach letter is then represented by its coordinates in the grid. The original square used the Greek alphabet laid out as follows: Letters are represented by two numbers from one to five, allowing the representation of 25 characters using only 5 numeric symbols. There are no surviving tablets from antiquity. The device partitioned the alphabet into five tablets with five letters each (except for the last one with only four). Basic form Īccording to Polybius' Histories, the device was invented by Cleoxenus and Democleitus, and further developed by Polybius himself. The device was originally used for fire signalling, allowing for the coded transmission of any message, not just a finite amount of predetermined options as was the convention before. The device is used for fractionating plaintext characters so that they can be represented by a smaller set of symbols, which is useful for telegraphy, steganography, and cryptography. The Polybius square, also known as the Polybius checkerboard, is a device invented by the ancient Greeks Cleoxenus and Democleitus, and made famous by the historian and scholar Polybius.
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