Say an ancient civilization that has excess amounts of copper, tin and lead but has no clear glass and iron.

They want to build a hydraulic telegraph system like the ones used by the Ancient Greeks but across their entire region. The geography is continous land instead of archipelago of islands.

The cost is not the concern and the land is not too treacherous while having water sources to facilitate this. So can hydraulic telegraph be adopted like telegraph system, how viable is this.

PS: They do not have horses or any draft animals.

  • $\begingroup$ The ancient Grecians did not use any kind of telegraph. No ancient civilization progressed past the level of simple semaphoric messages, usually transmitted by means of fires lit up on towers. The curious contraption described by Aeneas Tacticus that you refer to was never actually used in actual practice to transmit actual messages. For all practical purposes, if the richest man in the ancient world wanted to send an urgent message to the second richest man, the best he could do was to hire a courier riding the fastest horse money could buy. $\endgroup$
    – AlexP
    Commented May 26 at 12:37
  • $\begingroup$ As in... your world has no access to electricity? What's the tech level of your civilization? (What does "ancient" mean?) and what, specifically, are the missing resources (because I can make an electrically-driven telegraph without glass or iron...). I ask because those limitations might (and probably will) impact the reasonable development and deployment of a hydraulic telegraph. $\endgroup$
    – JBH
    Commented May 26 at 17:55
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    $\begingroup$ I would think that if the stations are close enough to use flares for synchronization, they could just use the flares as the direct signal-carrier without the complication of water. $\endgroup$ Commented May 26 at 23:45
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    $\begingroup$ @AlexP : there were faster ways, especially if the distance was longer than a few hours worth of ride: to maintain waystations for replacement horses. Or pigeons, which were in fact used even in ancient times. $\endgroup$
    – vsz
    Commented May 27 at 6:45
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    $\begingroup$ You may want to read Lest Darkness Fall by L. Sprague de Camp. The hero, having been thrown back into the post-Roman Empire time, tries to stem the tide of history that would destroy the remains of antique civilization and bring about the middle ages. He backports a number of technological and cultural aids to that end, among them a semaphore system. (It is not hydraulic though.) The novel is recommended because de Camp tried to realistically show the obstacles a modern person would face. $\endgroup$ Commented May 27 at 10:26

3 Answers 3


Modern testing of the Greek hydraulic telegraph shows that it can reach a transmission rate of 151 letters per hour.

On not so treacherous land other means of communications might achieve similar or even faster transfer rates: a messenger on a horse or on a boat, fire beacons, homing pigeons and so on.

The only place where I can see this being advantageous is somewhere making the above ones ineffective.

  • $\begingroup$ en.wikipedia.org/wiki/Underwater_acoustic_communication : There is this boundary layer effect, couldn't find it in the wiki, but basically sound propagates really far in the ocean, when reflected between cold/warm water layers. Just an addition, the answer is basically good as it is. $\endgroup$
    – Pica
    Commented May 26 at 22:25

The biggest problem i see with the hydraulic telegram system like the greek used it, that it still needs a certain line of sight for the syncronisation of sended messages. As i only read it on wikipedia, they still used a torch for starting the message delivery and syncronising the emptying and filling of the containers.

While greece islands where only seperated by what, you could see the lights over a long distance over the water. As soon as you work over land, you got the difficulty of elevation, flora and (yes) fauna, that could block the light. That would reduce the usefulness of that method drastically. to where it might just be more useful to send someone walking to send a message

Alternatively you could have a high tower - basically a light tower - that acts as a sending or reciving tower. That way you could increase the range for messages, as long as the tower is visible. This would you have a central communication hub for sending or recieving messages.

If you would have one reciever to one sender correlation, that would work, but as soon as you got more senders, you cant assure that the sender and reciever get syncronised. If two senders send a message at the same time, how could they figure out, whose message the reciever is ready to recieve?

You could have several reciever for one sender, if you skip the syncronisation part. Basically sending out a signal "im gonna send soon", and then send a second signal with the certain lenght of the message. This could be prone to failures.

Also you could relay messages from one tower to another, if you have a way to focus the signal to a certain direction, so only the reciever gets the signal. Else you would have the effect of the beacons of Gondor.

Anyway. i dont think it would be practial to have that system over longer distances, if you would have more than one possible sender. Over land, you could just have a messanger by foot send the message. Multiple reciever would be possible, if you adapt the system to not syncronise sender and reciver, but only send out a notice by the sender for the recievers to recieve a signal.


I think "hydraulic" is a misnomer for the Greek system, it is a Semaphore.
And yes it would work, but there are other semaphore systems that might work better for your scenario.

Things to consider are:

  • Does it need to work at night?
  • Can the operators at the endpoints of the semaphore lines expected to be literate? If yes, sending letters/digits becomes an option.
  • What is the symbol transmission rate? A low rate will restrict them to predetermined messages, with a higher bandwidth you can encode many more messages until you arrive as free text, maybe in the form of cleverly arranged symbols, or in the form of letters/digits.
  • What are the costs of building and operating a semaphore line, and is it within the reach of the operating state?
  • How centralized is the state: Would each pair of communicating endpoints have to set up their own code and conventions, or are there central academies with enough competent specialists that they will systematically determine what the best (cheapest/most reliable/fastest) way to set up semaphore lines, and everybody will just pick that up because they know that academies generally give good advice?

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