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Nowadays distance between countries doesn't matter too much. One of the United State's worst enemies is on the other side of the world! There have been wars that are fought thousands of miles away from the borders of countries it affects. But in medieval and ancient times, there were no planes or fast methods of transportation.

But how far apart exactly can two countries be in an ancient world? Pretend that there are no oceans and the world goes on forever. If two countries were once the same people, at what point would communication be impossible? If there somehow was a very, very large gap between these countries, what methods could these countries use to at least stay conscious of each other over long periods of time? Remember, this is theoretical and is not about Earth.

(Edit: These countries only have horses as the fastest method of transportation. This other world has a climate like Middle-Earth in the fact that it has the same relative temperature but the biomes, landforms, and most things vary. Ancient means about 2,000 years ago. Remember that this question is about the maximum number, because I mean like the distance can be much bigger than Earth itself.)

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  • $\begingroup$ If it's not about the Earth we should at least know climate you think about, is it jungle or plains or what, how do rivers work, why would people migrate and why they stay in touch. $\endgroup$ – Mołot Jan 31 '18 at 20:26
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    $\begingroup$ Be more specific with 'ancient times' as that could represent 1k to 50k years ago pretty readily. Trade routes hooked up Portugal to China in 'ancient times'...would be very hard to provide an exact answer here. Also need to know 'relationship'...an average Roman likely didn't know of China, however trade routes linked the two. What qualifies as a 'relationship'? $\endgroup$ – Twelfth Jan 31 '18 at 20:29
  • $\begingroup$ similar and with fine answers: worldbuilding.stackexchange.com/questions/13/… $\endgroup$ – Willk Jan 31 '18 at 21:02
  • $\begingroup$ The crusades happened over a pretty long distnce $\endgroup$ – Ovi Feb 1 '18 at 4:33
  • $\begingroup$ Note that if your world is larger than the Earth it's going to have stronger gravity, unless you handwave that away. $\endgroup$ – Wayne Werner Feb 1 '18 at 15:09
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I know you are expecting a distance answer but I'll give a time answer.

A good rule of thumb is a maximum of one to three months of travel. There are exceptions, but most civilizations that have direct contact are no more than one to three months away from each other. The distance varies with the terrain and type of travel.

Most of the time when distances were greater than that, the contact would be indirect. Europe had silk from China but they didn't have direct contact with China until Marco Polo. Instead, there was a chain of contacts that got the silk, eventually, to Europe.

Distant civilizations were exotic and mostly unknown quantities. They were known through tales of intermediaries. Most of those intermediaries (traders) had an incentive to exaggerate in order to make the origins of their wares more exotic and appealing or make their adventures sound more exciting.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – Monica Cellio Feb 4 '18 at 22:24
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You ask

at what point would communication be impossible?

Technically speaking I don't think it would ever become impossible. Though it would probably become too delayed to be of any real utility.

For example the Pony Express (USA circa 1860) was able to get a letter from the Atlantic to the Pacific in just 10 days. If we estimate that distance at 2,362 miles, that's about 236 miles a day.

So, for example, let's say that your two countries are 86,140 miles apart. It would take one year to get a letter from one country to the other. For most purposes if it takes you a year to ask a question and another year to get a response you can't really do much with that. I suppose you could have a pen pal that you only write every other year. But controlling business, governments, or military at that rate of communication would be very very hard if not impossible.

In Short:

The duration of the communication can't be longer than the amount of time in which decisions need to be made from the information that needs to be communicated.

So if you're using the Pony Express and you can wait two years before deciding on a course of action then your empires can be 86,140 miles apart. If you can only wait 20 days then they can only be 2,362 miles apart.

You also ask:

what methods could these countries use to at least stay conscious of each other over long periods of time?

As already mentioned the Pony Express was rather effective and the most advanced technology they used were saddles. The Mongol empire also employed a similar system of horse borne messengers called Yam. see here.

If we want to get really creative perhaps we could set up a system of mirrors, each just barely within sight of the others. Messages could be flashed by fire light from mirror post to mirror post much faster than a horse could travel.

But in both cases of horse stations or mirror stations the logistics of keeping the outposts supplied with workers and food would be a nightmare. I suppose you could get rid of the need for logistics for each outpost (mirror or pony) if they were self sufficient and could grow their own food. But as time goes on some of those outposts are likely to revolt. And if just one station stops receiving and relaying messages the whole thing breaks.

You would have to plan a year in advance to make sure food gets to the farthest station and what do you do if something happens to the food while in transit? or what if bandits kill all the workers as one of the stations? It would take you any were from 1 month to a year to respond and fix the situation.

Either option would require an amazingly dependable and robust logistics system.

Edit: apparently the mirrors have been used in real life see Semaphores. Usually with in the scale of countries such as France and Germany. Thanks to @jdunlop for the link!

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    $\begingroup$ It doesn't require an amazingly dependable logistics system, just normal employment-style logistics. Example: en.wikipedia.org/wiki/Semaphore_line $\endgroup$ – jdunlop Jan 31 '18 at 21:00
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    $\begingroup$ @jdunlop I did not know about Semaphores that's dang cool. I still maintain that maintaing a line of Semaphores (or horse stations ) that is 86,140 miles long would be amazingly amazing. You would have to plan a year in advance to make sure food gets to the farthest station and what do you do if something happens to the food while in transit? or what if bandits kill allthe workers as one of the stations? It would take you anywere from 1 month to a year to respond and fix the situation. $\endgroup$ – Dan Anderson Jan 31 '18 at 21:09
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    $\begingroup$ @jdunlop, Ya I mentioned self sufficiency as an possible option. But you still have to get the pay roll to them. And you what about bandits, or an invading army. If the land is pleasant enough to support a large enough population to man a fort then your going to get other peoples wanting some of the land and now you have to get an army involved. $\endgroup$ – Dan Anderson Jan 31 '18 at 21:21
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    $\begingroup$ And what if a station 6 months away starts feeling like they don't need the empire, and would rather go it alone? At some point the return on investment just is not worth it. $\endgroup$ – Dan Anderson Jan 31 '18 at 21:23
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    $\begingroup$ It is impossible on an Earth-like world for countries to be 86,140 miles apart. $\endgroup$ – Azor Ahai Feb 1 '18 at 0:49
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But how far apart exactly can two countries be in an ancient world?

Well, the distance between Portugal (Celtiberia) and China isn't enough, since in the 1st century BC there are traces of commercial relationships between the Han empire and the Roman.

In those same years the Roman poet Catullus wrote, Furi et Aureli, comites Catulli sive in extremos penetrabit Indos - relations with India and the Pandya Kingdom also existed.

Given sufficient reason (spices, jewels, luxury items...), and knowing that voyages lasting several years weren't so uncommon, I suspect that "too great a distance" ought to be great indeed. Geographical obstacles might be necessary.

Maximum distance traveled would depend on the availability of roads (a good Roman road allows around 100 km/day), rivers, local geography and climate, and travel organization (karwanserais can significantly speed up travel times; the possibility of quickly buying and selling one's merchandise, and resupply for the next leg of the trip, also strongly influences the duration of each stop), and of course technology (carts, harnesses) and beasts of burden.

A quick back-of-the-envelope calculation gives me a maximum distance - before travel time becomes unreasonable - of about fifty or sixty thousand kilometers, somewhat more than the 44.000 km of the Earth's circumference. This means a planetary circumference of up to 120,000 km, or a radius three times Earth's. A planetary network of Roman roads and good carts more than triple that figure. On the other hand, anything making travels difficult will reduce the maximum distance.

Above that, merchandise and information may still travel, just more slowly: as in the ancient times, stuff traveled between Aden and India, then someone else would pick it from Aden towards Alexandria, and so on until Rome. A packet might then well take twenty or thirty years to travel from one end of the trail to the other, often "waiting" in the middle for merchants going in the right direction.

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  • $\begingroup$ There were no direct diplomatic relationships between Rome and China or even Rome and India though? They knew of each other, but that was all. $\endgroup$ – Hegolin Feb 1 '18 at 18:06
  • $\begingroup$ @Hegolin there's nothing in the Question restricting it to "direct diplomatic relationships". Just... "relationship". $\endgroup$ – RonJohn Feb 2 '18 at 3:09
  • $\begingroup$ Not sure if one can call that a relationship, they kind of knew that there was something on the other end of the world. Just knowing that something exists is not really a relationship, I'd say. $\endgroup$ – Hegolin Feb 2 '18 at 21:03
  • $\begingroup$ @Hegolin, they knew there was something and they purchased that something. Pliny the Elder bemoaned the money spent in the remote East for women's silks. India supplied pepper and turmeric - more a status symbol than a spice, really, but still. $\endgroup$ – LSerni Feb 2 '18 at 22:54
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It doesn't matter how far away they are if transport tech can reach. Pilgrimages sometimes took years and people made up their wills before leaving.

All that matters is that the places in between are not hostile or too dangerous and that terrain is passable.

There are a few reasons a people will split, either expanding into another area, or civil war. Colonies can stay in touch with the founding place, because normally they would be colonised somewhere reasonably easy to get to. Trade colonies even more so.

Civil war is another matter, logically the losers would go as far as they could and sever relations with the original homeland.

Distance isn't an issue, it just means journeys take longer. If there is a need for the journeys, they will still happen, and the need can be as simple as socialising. Polynesians undertook dangerous and long voyages just to go and have a party with the inhabitants of another island.

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    $\begingroup$ @kingledion "It doesn't matter" that means infinity, which is a number. $\endgroup$ – LateralTerminal Jan 31 '18 at 20:37
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    $\begingroup$ @kingledion then make your own answer, comment and downvote are both lame... but que sera sera $\endgroup$ – Kilisi Jan 31 '18 at 20:40
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    $\begingroup$ @kingledion the question "at what point would communication be impossible?" is answered by "It doesn't matter how far away they are if transport tech can reach." That's an answer. It doesn't need a number attached. OP never asked for a number. $\endgroup$ – LateralTerminal Jan 31 '18 at 20:42
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    $\begingroup$ how long it takes the message to get there does matter if it takes 10 years one way then the ability to communicate is practically useless. $\endgroup$ – Dan Anderson Jan 31 '18 at 20:53
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    $\begingroup$ Infinity is not a number, but that doesn't matter either. Without an explicit reason why they can't; there's no reason why they couldn't. All that maters is if the area is traversable. $\endgroup$ – Mazura Jan 31 '18 at 23:40
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Natural barriers besides oceans exist. Deserts, mountains, thick jungle, volcano activity, and canyons are a few I can think of right away.

It can't just be about mileage, it's also got to be about conditions.

And beyond land conditions, it's also about what's profitable and the particular culture present in the land politically and religiously.

For example, the technology existed for China to be connected with the rest of the world, and they were certainly aware of other places, but they cut ties with everyone after a period of exploration in the 1400s.

Some of this was due to natural borders such as mountains, but mostly it was because they CHOSE to do this. Take a look at the top answer on this history stack exchange question as to why. While there was some trade, it was illegal, and China chose not to have relations with other countries.

You'd probably like a specific mileage number, but actually this question is impossible to answer without taking into account a lot of other things-- from how fast their system of travel and communication is. In a fantasy world, even with ancient tech, you would be surprised what you can accomplish, from a pony express type set up, to the clacks as in the Pratchett novels. All you really need for clacks is a good line of sight, ability to code (which the Romans even had), fire for light, and the ability to block the light periodically or a shiny surface to flash it, to send code.

My answer is two fold actually: as many miles as you please, given items to trade, easy travel, a method of connected communication, the correct political conditions (not an isolationist government). Alternatively, no miles at all, given land barriers, isolationist countries in between even friendly countries, no need for outside trade, and no ability to communicate over long distances.

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  • $\begingroup$ I would actually think of an ocean more as a connector, not a barrier. $\endgroup$ – Paŭlo Ebermann Feb 2 '18 at 1:50
  • $\begingroup$ @PaŭloEbermann Before the Age of Exploration it was largely a barrier. Lots of hazards to traverse, storms are largely fatal. Hard to communicate across. While some did travel, with enough ocean between continents it wasn't convenient. $\endgroup$ – Erin Thursby Feb 2 '18 at 2:19
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As a reference point I will use biggest empires. It's obvious that to become a part of empire, some region has been contacted and had some trade routes. I suppose 'have a direct route trade' means 'have some relationships'. You could look at ancient empires and which contacts they have. This is a lower limit. I would say that at least some thousands kms is not enough to prevent contacts.


Curiosity and greed are unlimited. The common pattern in trades is 'find out who sell goods to your contractor and then create a direct relationship'. There are many reasons to have no relationships with neighbors of your neighbor:

  • Expedition could take too much money
  • You don't need anything right now from them
  • They are assholes and have different color, language or religion

But the geography is not a reason. It's just a factor which could complicate communication. If you have some needs (spices, money, ally etc) from neighbor of your neighbor of your neighbor then you'll establish relationship. An embassy is a solution for bad communication.

So if between you and kingdom-far-away there are people communicating with each other then you sooner or later will be awared about it. If you aware and want something then you could contact. Probably you could get this with someone near you (like Greeks get silk from neighbors but not form China directly) but the distance can't prevent contacts.

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Several other answers explain well the difficulties of the geography and the limitation of communication. But there are other factors that need to be taken into account. In particular, the cultural aspect.

But before we come into that, let us clarify some points.

Ancient Europe did trade with Asia

Rome and India did trade over the Indian Ocean. Actually the Greeks and probably the Summers did it before them.

China

It is very likely that some in Europe were aware of China (India is clear) much before Marco Polo. Others already mentioned the silk. But why do we have the feeling that European were oblivious of China? Partly because the trade were reduced to some rather low, but essentially because the European civilisation left the Eastern part of the Mediterranean. And another civilisation flourished there, the Arabs/Persian.

European were often at odds with them throughout the Middle Ages (to say the least), but it did not stop the trade between them. It did, however prevent some extensive direct trade between China and Europe. Instead, that trade was made by the intermediate of the Arabs/Persian. The path was cut. It is still likely that some traders were aware of the origin of those goods.

The contacts became more known after Marco Polo and Ibn Battuta's travels.

Maximum distance for contacts

That is a complex question. First of all, due to communication issues, it would be hard to get the largest portion of the population interested in events happening many thousands of kilometres away from them: if you have a hostile army at your door, you tend to put a bit more interest in it than if the same army is at the other side of the world.

Nobles/leaders interest could be much higher. Especially if some trade is possible, or there are some real needs. But for that to effectively work in the ancient time, you need to make sure that your communication way does not get cut off. In particular, no new civilisation pops in between.

Conclusion

Regardless of the distance, the contact would be kept as long as the different civilisations are kept in direct contact and trade is possible and interesting.

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