The semaphore is a visual signaling system that generally uses flags or lights. Both the ancient Greeks and the Romans signaled over short distances with torches and flags. The telescope, invented around 1600, greatly increased the range of semaphores systems. In 1794, Claude Chappe, a French engineer, devised a semaphore that could carry a message 144 miles from Lille to Paris in two minutes. He constructed a series of towers about 5 to 10 miles apart and within sight of each other. On each tower was mounted a pivoted beam with arms at the end. A telescope was located at each tower so that an operator could relay the beam-arm signals.

       The electric telegraph replaced Chappe's semaphore for long-distance signaling in about 1850; however, Hutton Gregory, a telegraph engineer on the British railroads, modified Chappe's system by employing moving metal arms or rows of lights, mounted on towers, to signal trains. The railway semaphore is still in use.

       Semaphores also remain in use for maritime communications. The U.S. Navy uses a system in which an operator grasps half-red and half-yellow flags; the arms are extended at various angles to indicate letters of the alphabet.