Optical communication. Historical artwork of a system of communication using a series of torches to indicate letters of the alphabet. This system was described by the Ancient Greek scholar Polybius around 200BC. A system of ten torches and two walls were used to spell out words by their constituent letters according to a grid of coordinates. Two torches on the left and one on the right, as seen, might indicate the letter 'B'. From La Telegraphie Historique by Alexis Belloc (1888).