When writing any story, whether your characters can receive communication in time during a critical moment often makes or breaks a story. What makes or breaks this element of a plot is the kind of communication technology that is available in the setting. The setting itself will be shaped, subtly or overtly, by the intensity and ubiquity of communications, an observation that may be obvious in the early 21st century real world, but which also holds true in every time and place in real life, as well as in any setting a worldbuilder creates. Considering what sort of possibilities a given level of communication technology open or forbid can add a lot to your world.
Walk and Talk
Starting with the simplest methods, the human voice unaided can convey information effectively enough (so effective in fact that face-to-face communication has often been cited as being unmatched by any known technology), but its range is very limited, normally around 600 feet. Whistling languages like Silbo Gomero have a better range at which they are still intelligible, up to five kilometers in ideal conditions. There is a recorded case of a human voice being detectable at seventeen kilometers at night over still water, but of course one cannot rely on optimal conditions for a communication system. Combining the human voice with physical transportation, usually walking or running in the lowest-technology societies, is the primordial method of communication and should be available in nearly any world.
In fact, for almost all of human history up to the past few centuries, information was very often conveyed using the same techniques as physical goods, ranging from walking or running in the earliest societies to ships and horseback riding in more advanced societies. The invention of writing, which enabled letters and notes to be sent as opposed to pictures and memorized verbal communication, probably ranks as the most important development of the pre-modern period in this field, leaving aside physical transportation technology. Any worldbuilding taking place in a lower-technology or even pre-modern setting may be wise to take this into account. Medieval fantasy in particular commonly relies on horseback rider couriers to carry information, as was the case in the real medieval period.
These sort of methods may be more important in the future, or in a science-fiction setting. There is speculation that transmitting information across interstellar distances by radio or laser may prove very difficult compared to physically sending a small, perhaps microscopic, probe to the destination which would then transmit the information at a shorter range. Such a probe could easily be sent at relativistic speeds by laser beam propulsion. Ronald N. Bracewell first proposed this as an alternative to radio in a 1960 paper, and such probes are commonly called Bracewell probes in his honor.
Smoke Signals
There are other possibilities, however, even with primitive technology. Smoke signals are probably the most famous primitive method of communicating over long distances: visible smoke from a fire rises surprisingly high up, and can transmit information much faster than a traveling man could. Native Americans are probably the most famous users of this technology, and it was so effective that Lewis and Clark adopted it during their expedition. Americans weren’t the only users of this technology, though: it was employed in Australia, China, Europe, and likely beyond. To this day the Vatican uses a smoke signal during conclaves to communicate whether they have elected a Pope, and colored smoke grenades are used by militaries for various purposes. The Great Wall of China may have had the most extensive system, a sophisticated system being able to send signals hundreds of miles in a few hours.
The key disadvantage of smoke signals is that what can be communicated is limited, usually to just a few signals. In one native American usage positioning on a hill (halfway or all the way up) served to differentiate, and other systems, including some used by Aboriginal Australians, used colors. Whether the smoke is a column, ball, or smoke ring could also serve to differentiate, which was also used by the Australians. Since interrupting the signal is not nearly as easy as it is in Morse Code smoke signals historically were used to send pre-arranged messages, such as danger, attack, all is well, receiving visitors, to signal a meeting place, and the like.
A sufficiently sophisticated system, however, may be able to effectively convey alphabetic information. If one varied the colors between black, white, and blue, and varied the shape of the smoke between column, ball, and ring, then one would have nine distinct signals. If groups of multiple such signals are used, the number of permutations would be more than enough to represent any language. Fantasy worldbuilders take note! The downside to such a system is that to transmit, say, 100 characters perhaps several hundred smoke signals would be required. Even if we assume a distinct signal can be sent out once every minute, it would take several hundred minutes (or somewhere on the order of five hours) to send a 100 character message. If we give a range of ten miles between each signaler a human courier would get such a message there in roughly the same time by walking (let alone riding a horse or even a dog sled), thus offering little advantage to using smoke signals.
Obviously the frequency needs to be much higher than once a minute for this to work in a fantasy or low-technology setting. The one big exception I can think of is a setting where visibility is good but the terrain is very difficult to traverse, somewhere like a steep rugged mountain valley. A civilization that develops in such a rugged setting may find using smoke signals easier than physical couriers, and if conditions for development were otherwise favorable may use communications to overcome their terrain disadvantage.
Talking Drums
Drums are another possibility, being commonly used by indigenous peoples in tropical America, Africa, and New Guinea, the talking drums of Africa being the most famous example. Very rapid signals are possible and natural languages can be replicated, which seems very promising. White explorers in real life were often surprised to find that word of their arrival spread faster than they could travel, and black slaves in the New World used talking drums to communicate in a code unknown to their masters, apparently so effectively that they were banned. A talking drum message can reach three to seven miles out under ideal conditions and can reportedly travel up to a hundred miles in an hour all told, which is very fast for a pre-modern society. One of the key disadvantages is that, like smoke signals, it is usually an ambiguous method of communication, though it seems like it would be much easier to apply something like Morse Code to drums than smoke signals.
There doesn’t seem to be any particular reason why people in more temperate climates could not also use drums for this purpose, but for whatever reason only tropical forest cultures seemed to make use of them. As far as I’m aware the Chinese, Indians, and especially Europeans all had sophisticated drums in the pre-modern period but used them for battle and music rather than long-distance communication. Medieval European fantasy that featured Western-style drums being used like their tropical counterparts seems like a rather cool concept, one that may be quite fruitful for fantasy and alternate history worldbuilders to explore.
Lighting a Beacon
Aside from using fire to make smoke, fire can be used to send a signal directly. Primitive lighthouses essentially used this, sending a signal of their location to mariners as navigational aids. However, the beacon from a fire cannot be varied even as much as a smoke signal, thus limiting the signal to turning it on and off. Turning a fire on and off is a cumbersome process, but shades could be used to obscure the glow from the fire. Another possibility would be to use colored filters to change the color of the beacon, but since this reduces the brightness of the beacon it makes it less effective. Additionally, any culture sophisticated enough to use colored slides to change the color of the beam can also make much more efficient opaque shades.
In principle shades moving on and off the light beam could be done as rapidly as a telegraph, multiple times per second. Even moving shades manually can be accomplished multiple times per minute. Assuming a rate of a bit less than one character per minute (which could be accomplished with a fire, a manually-moved shade, and Morse code) a 100 character message could be transmitted in about an hour. This greatly beats walking and is competitive with horseback rider couriers, assuming a range of around ten miles. If one had a machine that could open and close the shades fast enough to transmit a character every few seconds, a 100 character message could be transmitted in a few minutes.
Assuming each station has a range of ten miles (on a hilltop, on a coast, etc.) and it takes five minutes to transmit between stations, a 100 character message could travel 120 miles in an hour. Now that’s fast. Such a level of technology would be well within the capabilities of many medieval fantasy settings, and would have implications for the spread of information. To their credit many creators of fantasy settings do just that; fire signals were used perhaps most famously in The Lord of the Rings (the warning beacons of Gondor), albeit without any Morse Code-like signaling. This is closer to fire signals’ historic application, until the past few centuries when optical telegraphy rose to the forefront. In particular, the Byzantine beacon system in real life was constructed along similar lines to Gondor’s in the Lord of the Rings.
Lighthouses, because they have an unobstructed horizon, have the longest range for beacons. A 50 foot tall lighthouse can be seen from a maximum distance of 9 miles, 15 miles for an observer 15 feet up. In general a beacon a few hundred feet tall will be able to be seen 20-30 miles out. A beacon like this if it could transmit at a rate of around one character per second could send a 100 character message in perhaps two minutes. With 20 miles between beacons a message could travel 600 miles in an hour over a network of such beacons.
Lighthouses on prominent points well above sea level have an advantage, of course, as do beacons located on mountaintops, as this increases visibility and range. Both the real Byzantine system and the fictional Gondor system used mountains extensively. Some of the Byzantine beacons were as far as 60 miles apart. Utilizing mountains would increase the effectiveness of either a real or fictional beacon system, and once again fantasy worldbuilders should explore the possibilities for beacons to become very important for civilizations inhabiting very rugged terrain.
A message traveling at 600 miles an hour could reach halfway around the Earth in 20 hours, assuming the entire world had a beacon system of the type described above. This isn’t quite as fast as modern telecommunications, which travel at the speed of light (traversing the same distance in 1/7 of a second instead of 20 hours), but it gets one most of the way there relative to medieval or earlier levels. Of course, this assumes that beacons are spread evenly, but if they are land structures they will be mostly limited to continents, thus places close by sea but not by land (such as South Africa and Patagonia) will take longer to receive messages. Conversely, places along tall mountain chains will achieve better visibility and will receive messages faster.
Flashing Mirrors
After you already have beacons, the next step up, aside from more intensive networks of beacons, is the heliograph, the using of mirrors to reflect sunlight and deliver messages by flashing the light to a particular location. This might seem like a simple technology but mirrors have to be of fairly good caliber to reflect enough sunlight to see from a great distance. You also have to have a fairly exact idea of where you’re aiming the light, which requires a level of science beyond the usual medieval standard. Accordingly the first heliographs (of the modern tradition; there is speculation they were used in classical antiquity) were deployed in the 19th century.
Where heliography beats the beacon system is its lightweight nature, being easily portable by a single man as opposed to requiring an infrastructure of towers. Heliographs are particularly effective in settings with bright sunshine, little cloud cover, and rugged terrain; their all-time height of usage was in the Boer War in South Africa during the turn of the 20th century, declining thereafter, though there are reports of them being used by Afghan military forces as recently as the 1980s.
Heliography has all of the same advantages as telegraphy, being equally well-suited to using Morse Code and similar systems, but using sunlight in place of electricity, thus being usable in more remote locations. Signaling with mirrors didn’t get that much usage in real life because the telegraph proved superior in around the same era, but it should be noted that a civilization where optics developed much earlier relative to electricity could easily have a long period where heliography is by far the best long-distance communication technology available. The implications of this would be similar to the beacon system but far more intense as it would be more widely usable and thus denser.
An Ancient or Medieval Internet?
Compared to a beacon network, a heliograph network would enable far more data to be transferred in the aggregate. Similar to the telegraph it could in principle be machine-operated and be run at the household level, thus being more decentralized. Ringing a bell yet? This is the same general principle as the Internet! Obviously the transfer speeds would be very slow compared to even dial-up, but consider that the earliest computers exchanged data with each other over telephone lines. Exchanging data over a telegraph line isn’t much different (in fact the telegraph seems to lend itself more to computer operation than the telephone system). The only thing that prevented such an Internet from appearing as early as the mid to late 19th century is the lack of computers.
Early computer technology is a much-discussed “what-if” topic of alternate history which we won’t get into here, but the point is that the same principle that enables the telegraph to function as an Internet would also apply to any system capable of carrying rapid Morse code-style signals, including the heliograph. Such computer technology would ordinarily be concomitant with industrialization. After all, even Charles Babbage, often cited as the earliest computer pioneer, was operating long after the industrial revolution had started. Babbage’s computers were mechanical (or analog) as opposed to digital, however, and if the famous Antikythera mechanism is any indication the ability to manufacture such devices dates back much earlier.
Based on these premises, a civilization that developed optics much earlier, had relatively sophisticated science, and had a pre-industrial understanding of computers comparable to the ancient Greeks could have computer-operated heliographs (or various other signaling devices) in many households and businesses long before the industrial revolution came around. The upshot of this is not so much creating an early industrial revolution, but rather that a chance exists in alternate history or realistic fantasy to have a mass communication system similar to the modern Internet in an otherwise pre-modern, medieval, or ancient setting. That’s a fascinating possibility.
Such an Internet would not be nearly fast enough to support the rich graphics we see today, but would rather almost certainly be text-only in output, like Usenet. Advertising on websites to support them would be harder (but, alas, not impossible), but it seems likely that such a stone-knives-and-bearskins-style Internet would feature mostly businesses running e-commerce (which was already a thing in the 1980s in real life, albeit very marginal) and non-commercial hobbyists running web forums and the like, along with more direct peer-to-peer communication.
Conclusion
This rundown of the options for primitive communication by no means covers all the options. The optical telegraph, for instance, also covers such methods as having towers give flag signals similar to semaphore instead of lighting beacons. A hydraulic telegraph uses water pressure through pipes to raise or lower water, the water level sending messages similar to smoke signals. Signal flares can also be used to send messages, for instance by using a primitive rocket (similar to those used in medieval China, which could plausibly have been developed much earlier) that puts out a specific color of light, or even fireworks. Along the same token smoke signals can be and are actually used by aircraft to send messages, and it is easy to imagine gliders or hot air balloons being widespread in an otherwise ancient or medieval setting.
Another possibility is using domesticated or tame animals to deliver messages, such as birds that can be trained to navigate to specific spots or in specific directions, most famously the carrier pigeon in real life. Pigeon-carried messages, or messages carried on a similar creature in a fictional setting, would easily beat most of the methods in this post, and indeed in remote areas with slow Internet pigeons carrying computer data have actually proven in some instances to be faster than more conventional methods.
What we see with all this is that even without electricity or industrial-level technology there are many communication technologies that an ancient or medieval civilization in a speculative fiction setting could adopt on a mass scale that would be greatly superior to what real-life ancient and medieval civilizations had. Combining ancient technologies enables us to go even further than the Victorian Internet to an outright Ancient Internet. Many of these ways of communicating aren’t very common in contemporary science fiction, alternate history, and fantasy works, and would add much to almost any setting in these genres.