The semaphore flag signalling system was developed by the Chappe brothers in France in the late 18th century.
They determined by experiment that it was easier to see the angle of a rod than determine the presence of a panel. Their system was composed of black movable wooden arms, the position of which indicated alphabetic letters. The Chappe system was controlled by only two handles, was mechanically simple, and reasonably rugged. Night operation with lamps on the arms was unsuccessful.
The arms showed seven positions each, and the connecting cross bar had four different angles, for a total of 196 codes. A crucial innovation was to use a group of trained, dedicated men to pass the signals.
The first Chappe semaphore line was established between Paris and Lille in 1792. It was used to carry dispatches for a war between France and Austria. In 1794, it brought news of a French capture of Condé-sur-l’Escaut from the Austrians less than an hour after it occurred. Other lines were built, including a line from Paris to Toulon. The system was widely copied by other European states, and was used by Napoleon to coordinate his empire and army.
The first symbol of a message to Lille would pass 120 miles through 15 stations in only nine minutes. The speed of the line varied with the weather, but the line to Lille typically transferred 36 codes, a complete message, in about 32 minutes.