Probably the first sucessful long distance text messaging system was the Chappe semaphore system deployed in France around 1800. Its derivatives are still used today.

Semaphore / Mechanical Telegraph Systems

The Polybius digital communication system became a practical about 2,000 years after it was first proposed. In the early 1600's the optical telescope was invented, and humans gained the superhuman eyesight they needed to read Polybius' torches at great distances.

The light from torches are not usually visible in daylight, and the smoke from the torches would quickly combine to make it impossible to tell how many torches were generating the smoke. As a more practical alternative, people used large movable panels, as illustrated below.


There were many variations on this theme. The most prominent was the Chappe system deployed in France in the late 1700's. It was originally intended as a military communication system, but later was pressed into service to send important national news such as lottery numbers. Claude Chappe, the developer of the system, coined both the words semaphore and telegraph to describe its operation. Semaphore literally means sign-carrying, and telegraph literally means distant-drawing. We still use the term "carrier" to describe a part of modern electronic communication systems. And of course telegraph spawned other words like telecommunication, telephone, teletype and tele we meet again.

Eventually the term telegraph was taken over by the electrical communications people, so we more commonly use the term semaphore to describe the Chappe system today.

In the Chappe semaphore system, characters were transmitted using a large movable structure that had three arms. It looks somewhat like a person extending their arms, and flexing them at the elbows. The three arms could be rotated into different orientations, to indicate the letter being transmitted.

Semaphore Code Book

The arms were made long enough that they could be viewed through a telescope from approximately 20 to 30 kilometers away. The received messages were then relayed down the line to effect cross-country communication. At it's peak, the Chappe system consisted of a multiple number of lines that spanned the country of France


Like all mechanical telegraph systems of this type, the system had some limitations. The transmitting and receiving locations needed to be on towers, or placed on high points, so they could have an unobstructed view of each other. Rain, fog, and other weather conditions could obscure the distant stations, preventing communication. If bright lamps were attached to the arms, the system could be used at night. But in the days before electric lights, it was difficult to get small lamps that were bright enough to be visible from 30 km, so in practice the Chappe system was primarily used during daylight hours.

The semaphore system was not secure, in many ways. Eavesdropping on someone else's conversation was trivial. The transmitting stations were very prominent, so it was easy to find a location where an unauthorized user could copy down the message. The system was also subject to man-in-the-middle attacks. As described in the Count of Monte Cristo, all it takes is one corrupt operator at a relay station, and you could change the message to anything you wanted. Encryption was needed if you wanted to make sure others could not read your message, or if you wanted to be able to detect that it had been modified.

While the Chappe telegraph was incredibly slow by modern standards, it never the less allowed messages to move across the country of France in about an hour. That is far faster than a messenger could move at that time. The difficulty of building a Chappe station, the large number required, and the expense of staffing them, limited its use.

Modern Semaphore Systems

Variations of the Polybius digital communication and Chappe semaphore systems, are still used today.

In the early days of rail travel, people used semaphores to get messages to passing trains. The semaphores told train operators if it was safe to proceed, or if they needed to slow or stop. Today drivers, and train operators, use multi-colored traffic lights for this purpose. But when trains were first deployed in the early 1800's, the electric light had not been invented, and there were no small, inexpensive, reliable, and low maintenance lamps that were bright enough to be visible in daylight. So a movable panel, or semaphore, was the way to go. Lights that allowed the signal to be viewed at night were sometimes added.


Hand-held flags are used on ships to send messages to nearby vessels. While far slower than electronic communication, it does not rely on any advanced technology - and it is nearly impossible to detect the transmissions from beyond the horizon. If you are maintaining radio silence to help conceal your position, then using semaphores rather than radios can be helpful.


There are some environments where ambient noise is so loud that voice commands are impractical even for short distance communication. A semaphore like system of hand signals can be used. An example of this is aircraft marshalling. This system is used by ground personnel to tell pilots where to move their planes.


Crane operators also receive hand signals


Those with hearing challenges can use their digits for communication, using sign language that is far more complex and expressive than anything Polybius suggested