The Polybius square is a classical cryptographic tool that is used to encode letters into pairs of coordinates. It was named after the ancient Greek historian Polybius, who is often credited with its invention. The square consists of a 5x5 grid that contains the letters of the alphabet. Since there are 26 letters (the English alphabet) and only 25 spaces in a 5x5 grid, one letter is typically omitted or combined.
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