I'm trying to think of ways that a humanoid civilization, post-agrarian with solid mechanical knowledge but no electronics, can communicate in near real-time over large distances.

Some of my initial ideas include communication by light towers, which would allow for direct site-to-site communications and would have interesting side effects of being ineffective during inclement weather; and communication by ground vibrations, which would allow for broadcast communications.

I'm trying to get more advanced than communication by messenger (although that may be a backup plan for the light towers) but I don't want to introduce electronics into the culture.

I'm looking for something scientifically plausible.

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    $\begingroup$ The clacks $\endgroup$ – Separatrix Nov 11 '16 at 17:07
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    $\begingroup$ Please edit to clarify: do you need wireless? Do they have (wired) electricity? Electricity is not the same as electronics. $\endgroup$ – kubanczyk Nov 11 '16 at 21:47
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    $\begingroup$ Large distances on-planet or through space? $\endgroup$ – Zxyrra Nov 12 '16 at 0:11
  • $\begingroup$ Have a look at en.wikipedia.org/wiki/Railway_semaphore_signal, they are mechanical. For the people operating the signals to communicate, they use a bell system - maybe see how that is done. $\endgroup$ – Tim Nov 12 '16 at 17:47
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    $\begingroup$ Fast as bandwidth, or fast as in latency? $\endgroup$ – March Ho Nov 12 '16 at 22:35

10 Answers 10


Lookup the Discworld's Clacks system. It started out as a series of semaphore towers, with two flags at the top of a tower sending alphabetic messages a letter at a time to another tower, which then relayed the message onward along a string of towers. Over time, it became more and more elaborate, replacing the simple arms with grids of squares that could be open or closed to send messages, and more and more elaborate compression algorithms were developed - all done mechanically, with no hint of magic or electronics. It was designed by Terry Pratchett to be a logical extension of the early optical telegraph systems, which were being used as early as 1793.

On the Discworld, the Clacks developed its own subculture, with people sending c-mail to one another, and even developed groups of hackers.

  • $\begingroup$ And weather actually bothers them less than you'd imagine, they actually work better in the dark. $\endgroup$ – John Nov 12 '16 at 13:34
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    $\begingroup$ gnu terry pratchett $\endgroup$ – ankh-morpork Nov 12 '16 at 23:09
  • $\begingroup$ The semaphore towers in the movie "Going Postal" were based on this concept, and became a core plot element. $\endgroup$ – jaxter Nov 14 '16 at 2:45
  • $\begingroup$ heck the navy has been using signal lamps for forever, la-timonerie-antiquites.com/uploads/items/detail_maxi/… $\endgroup$ – John Nov 14 '16 at 4:40
  • $\begingroup$ As much as I admire Patchett's work, why reference the fictional Clacks when shutter telegraphs were real? $\endgroup$ – DevSolar Nov 14 '16 at 10:36

Telegraph. The world was linked by a mesh of long-distance telegraph cables long before the advent of electronics. Telegraph can work very well thank you without electronics. Or do you mean no electricity at all? Then historical experience says optical telegraph using semaphore towers.

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    $\begingroup$ I don't know why this was downvoted. The question asks for fast long distance comms without electronics, and the electric telegraph fulfils that exactly. "Electronic" and "Electrical" mean different things. $\endgroup$ – Lostinfrance Nov 11 '16 at 18:14
  • $\begingroup$ I didn't downvote, but you can clearly assume that the question meant "no eletrics". To quote: "solid mechanical knowledge but no electronics". Contrasting electronics to mechanics (instead of electrics) means the OP confused electronics with electrics. $\endgroup$ – AnoE Nov 12 '16 at 21:14
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    $\begingroup$ Historically, plain old electric telegraphy preceded radio by half a century, and this was in a world which was feverishly looking for a technology enabling efficient long-distance communications... Sometimes people forget that the electical telegraph is Victorian technology, roughly contemporary with steam engines. Stephenson's Rocket locomotive was made in 1829 and Morse's telegraph sent its first message in 1844. $\endgroup$ – AlexP Nov 13 '16 at 3:57
  • $\begingroup$ It should also be noted that Morse's telegraph was first very cheap telegraph. Many say he invented telegraph, but what he really did was promote invention of what is now called source coding. This allowed him to use simple binary signalling, allowing for one or two wire systems, instead of competing multi-wire systems. It is also interesting that facsimile system also comes from the same time period. $\endgroup$ – AndrejaKo Nov 13 '16 at 20:13
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    $\begingroup$ @AnoE You cannot assume that. The OP stated no electronics, and electronics are systems composed of devices that can produce power gain, such as transistors, vacuum tubes, etc. The telegraph has no such devices, as one example, nor do lighting systems or electric motor systems - they are purely electric systems. $\endgroup$ – jaxter Nov 14 '16 at 2:50

Use trembita pipes like this:


In good weather (without wind), the sound of trembita can be heard in few miles. There can be lines of trembita players, who can relay messages. But i think the light telegraph will be much faster. Furthermore, trembita and light telegraph can be combined in single towers.

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    $\begingroup$ Have you ever played telephone :p? $\endgroup$ – Ovi Nov 12 '16 at 23:20

As others have said, a Flag semaphore is a very easy optical communication method, where you substitute letters/numbers for flag positions. though bad weather would be a bit of a problem, And scaling it for distance would be hard (but telescopes can help).

Using smoke signals or reflected light, you can also do visual Morse Code.

Another easy method (at least for short ranges) is a simple Tin can telephone which is just cans connected by a string.

Where mountain ranges (higher than the cloud line) and other barriers become an issue, you might have to rely on carrier pigeon. Traditionally they only had a 'fly home' setting, but maybe you could train some bird to be a fast and versatile message carrier.

I should also mention that whistle languages exist for this very purpose. The range will be ~1-2km (~1 mile) on average, but you can get 5km in mountains and up to 10km in optimal terrain. (Thanks to the heavily studied language Silbo on the island of La Gomera in the Canary Islands) Obviously you could extend this range by using an interment to reach higher decibels or to hit a wavelength that will carry better in the local terrain, but the instrument will likely also limit the expressiveness of the language.

And if you want to push tech a bit, maybe you could use a hand powered vacuum tube message system.

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    $\begingroup$ Mountains and other barriers are more of an help than an issue. Plant your relays on top of them and you just got yourself tall relay towers for free. $\endgroup$ – spectras Nov 12 '16 at 7:23
  • $\begingroup$ @spectras Yes and no. If the mountain top is obstructed by clouds, or is unstable (volcano), than it can become a major hindrance (or at least require a bit of extra effort). Otherwise, yes, they are free tower bases. It was the most likely 'extreme barrier' I could think of other than 'small ocean' (I believe the great lakes qualify here) $\endgroup$ – Tezra Nov 14 '16 at 20:46
  • $\begingroup$ Volcanoes are even better. You just erupt it when you want a signal and it can be seen for miles. Classical techniques for controlling that do tend to require sacrifice of women, so you'd need to have many children to keep the population high. Pretty much no downsides, well, besides the difficulty of convincing the jealous volcano goddess that she should pump smoke out in any specific pattern. $\endgroup$ – The Nate Nov 15 '16 at 7:05
  • $\begingroup$ @StephanKolassa> Tolkien's watch tower seem to have been greatly inspired by the Byzantine beacon system, btw. $\endgroup$ – spectras Nov 15 '16 at 14:26

A borderline case: Fiber optics.

You can do this without even electricity but such a technology probably can't build the cables.

The transmitter uses lenses to focus the light onto the end of a fiber, the sender uses a beam interrupter. The signal itself is morse code. The receiver sits in a totally dark room so even a faint signal will be visible.

Unfortunately, your working range is only in the single digits of km per stage.


Signal fires are the most basic solution.

Classically, beacons were fires lit at well-known locations on hills or high places, used either as lighthouses for navigation at sea, or for signalling over land that enemy troops were approaching, in order to alert defenses. As signals, beacons are an ancient form of optical telegraphy, and were part of a relay league.

Systems of this kind have existed for centuries over much of the world. The ancient Romans used beacons ...

In the 9th century, during the Arab–Byzantine wars, the Byzantine Empire used a beacon system to transmit messages from the border ... to the imperial palace in the Byzantine capital, Constantinople. ... Beacons were later used in Greece as well, while the surviving parts of the beacon system in Anatolia seem to have been reactivated in the 12th century by Emperor Manuel I Komnenos.

In Scandinavia many hill forts were part of beacon networks to warn against invading pillagers. In Finland these beacons were called vainovalkeat, "persecution fires", or vartiotulet, "guard fires", and were used to warn Finn settlements of imminent raids by the Vikings.

In Wales, the Brecon Beacons were named for beacons used to warn of approaching English raiders. In England, the most famous examples are the beacons used in Elizabethan England to warn of the approaching Spanish Armada. ... In the Scottish borders country, a system of beacon fires was at one time established to warn of incursions by the English. ... The Great Wall of China is also a beacon network.

In Spain, the border of Granada in the territory of the Crown of Castile had a complex beacon network to warn against Moorish raiders and military campaigns.

Wikipedia: Beacon: For defensive communications

Danby Beacon by Jim Champion

Danby Beacon by Jim Champion (CC BY-SA 2.0)

Danby Beacon is at the summit of the aptly named Beacon Hill. The modern beacon sculpture stands on a Bronze Age burial mound, previously the site of a 1988 replica beacon and the original Armada-era beacon.


Jungle Drums. These can be heard several miles away, in any kind of terrain. And unlike signal fires and semaphores they do not require clear visibility (which, as any pilot knows, is a rare and fickle commodity). Nor do they require daylight (semaphores) or nighttime (fires).

Networks of drums were used to great effect in Africa, South America, and parts of Oceania.

There's a good Time Magazine article, but it's behind a paywall.


Strings running through pipes or guiding wheels over several kilometers with springs on either end to pull them back into neutral position. Theoretically you could connect a mechanical typewriter directly to the strings though a more sophisticated encoding would be advantageous. It doesn’t even have to be binary (string pulled or not pulled), you could implement several levels of pull.

Now that I think about it … it doesn’t even have to be strings, it could be hydraulic or pneumatic too.

Unlike other methods mentioned this would also work without a line of sight.

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    $\begingroup$ @Michael: I happen to come from the electronics side of things, which includes at least a basic understanding of transmission lines. Even though it's often applied to electronics, the concept applies to any system: mechanical, acoustic, etc. The idea is that a disturbance is actually sent as a wave that travels at the speed of sound for a physical medium or the speed of light for an electrical one, and it takes some time for that wave to reach the other end. (to be continued...) $\endgroup$ – AaronD Nov 13 '16 at 10:15
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    $\begingroup$ Where it gets interesting (and weird) is when the impedance changes, like from air to rock or from string to hook. In that case, some of the energy continues on through the transition and the rest bounces back the other way. When the reflected wave encounters another impedance change, like a similarly mismatched transmitter, some of the energy again continues through the transition and the rest bounces back the other way. Now the receiver gets multiple copies of the same signal, superimposed on each other with different delays caused by the travel time between mismatched impedances. $\endgroup$ – AaronD Nov 13 '16 at 10:20
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    $\begingroup$ For short lines (relative to the wavelength being sent on it), nobody cares about this because it has plenty of time to "ring out" before any appreciable change happens to the intended signal. But for long lines, the way to make it work anyway is to make the receiver behave exactly like the medium that leads up to it. A resistor across the end of a long electrical communications cable "looks like" an infinite length of cable, just like a carefully-designed and precision-manufactured stringlike-compliant hook can "look like" an infinite length of string. $\endgroup$ – AaronD Nov 13 '16 at 10:25
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    $\begingroup$ Get that right, and you'll accept all of the incoming energy, regardless of how long the line is, leaving none to reflect back away from the receiver and probably come back again to mess up your intelligibility because it bounced off the transmitter too. I've had exactly that problem with a string of DMX lights. Without the resistor plug at the end of the string, they all get confused. Put the plug on, and everything's good. Like I said to start this mini-lecture, the same concept holds true for any medium: mechanical, hydraulic, electrical, optical...anything. $\endgroup$ – AaronD Nov 13 '16 at 10:32
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    $\begingroup$ @Michael: When terminated correctly, you're right, it's just a question of latency, not bitrate. But the two hard parts are the termination and avoiding/handling any variations in impedance along the way. (pulleys on a string, for example) How much reflection is acceptable? Translate that to an engineering design with tolerances. Now, can your manufacturing facilities make that design and keep those tolerances? $\endgroup$ – AaronD Nov 13 '16 at 11:27

The answers by @LorenPechtel and @BrockAdams were what leaped to mind when I read your questions.

As small expansions on those answers, assuming that there is some allowance for scientific rule-bending (i.e. your setting is not historical or based completely on existing science/materials), two things I would suggest as possibilities:

  • Sound creation/amplification devices, with (temperature and pressure controlled?) fluid tubes to carry that sound.

  • Mirrors/Prisms (cut crystal) to redirect light through tubing, etc. as well.

But it could add a little flavor if need be. Remember that there are at least some people who suspect that ancient people had "lost techniques" we haven't yet "rediscovered" (or have otherwise obsoleted through modern technology).

  • $\begingroup$ What does «=P» indicate, and what is this tag that you cannot read? $\endgroup$ – JDługosz Nov 13 '16 at 12:04
  • $\begingroup$ Apologies for the confusion. The symbol is intended to indicate a face with extended tongue. Together with the statement, I intended to indicate that I am unsure of what "pseudo-science" (per the current "science-based" tag) consists of in terms of real scientific principles applied more liberally than might otherwise be (i.e. how hard is the communities opinion of hard-science). $\endgroup$ – Anaksunaman Nov 13 '16 at 13:21
  • $\begingroup$ Your preliminary disclaimer is sufficient in this regard. $\endgroup$ – JDługosz Nov 13 '16 at 19:51

Since we're in the realm of science fiction here, why not consider the ansible, of Ursula LeGuin fame and utilized by many writers since? There has never been any explanation of the technology; the only definition is its capability of communicating messages instantaneously across a galaxy.


protected by Monica Cellio Nov 13 '16 at 4:06

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