Almost as soon as writing was invented, authors have developed ways of shielding their materials from unwanted viewings. Polybius the Greek (c. 208-125 BCE) [first image] describes how two of his compatriots, Cleoxenus and Democleitus, developed a method of cryptography that now goes by the name “Polybius Square.” [See second image.] By placing the Greek alphabet on a grid, you can number the lines and columns so that each letter corresponds with a pair of numerals. If you look at the third image with the Latin alphabet, you can get a clearer sense of the pattern. These numbered pairs had the advantage of being able to be transmitted through torchlight, so that it served as a long-distance message system, perhaps for armies. If the pairs of numbers are translated to sounds, you can get a “knock code” going. More complex versions of this cipher are used today by computer encrypters.
Source(s): Image from Wikipedia. “The History of Cryptography” at cs.stanford.edu; Polybius _Histories_, book X, 45.6. Third image from “fineartamerica.com/featured/1-polybius-square-science-photo-library.html .
