In Shingeki no Kyojin humanity is confined within walls to protect them from giants on the outside.

In this case, I'd like to imagine a civilization (doesn't need to be all of humanity) within a huge walled "city", because there is great danger outside the walls.

How could civilization evolve such that this is possible?

These are my consideration and doubts:

  • There is a great danger outside the walls, which the walls can stop.
  • How could this civilization evolve enough to build such walls when there is that great danger?
  • Which danger makes sense while keeping it realistic? (I don't like the idea of giants suddenly appearing from nowhere)
  • EDIT: All known humans by such civilization live within the walls. (I put it in italics because there might be some kind of mutants outside)
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    $\begingroup$ This is essentially the plot of the classic sci-fi movie *Forbidden Planet". It is well worth watching if you haven't seen it. rottentomatoes.com/m/forbidden_planet Incidentally it is in full colour despite what the 'tomatoes' review seems to suggest. Here's the trailer youtu.be/8y4crGU7dkg $\endgroup$ – chasly from UK Jan 14 at 9:52
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    $\begingroup$ I'm not sure I get why this is a question. If we as humans, right now, decide that the outside is somehow "dangerous", we'd build a wall around us (no political joke) and live inside. We could have done this centuries ago. And we have in terms of cities and villages. We just venture outside the walls but assuming we have everything needed on the inside, we could stay inside. There doesn't seem to be any special evolution required to facilitate this aside from giving us a reason to stay in and motivation for walling in enough resources. $\endgroup$ – VLAZ Jan 14 at 10:25
  • $\begingroup$ I don't get how this is offtopic or deserves a negative vote. Anyone would mind to explain? $\endgroup$ – Masclins Jan 14 at 13:21
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    $\begingroup$ @Masclins why wouldn't your premise be possible? I'm not sure what is stopping you from doing that right now or with the human society from centuries before. Heck, China famously did build a big wall to protect it from outside threats two millennia ago. More recently, Berlin had a big wall, too. Less tangibly but still within the same idea - soviet republics were "contained" ideologically from the West. I'm not sure if that makes the question "offtopic" but I can't see how I can answer it as I don't see anything special that would prevent a society walling itself in. $\endgroup$ – VLAZ Jan 14 at 15:03
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    $\begingroup$ General Patton once said that "fortifications are monuments to the stupidity of Man." This concept is parodies in the movie Pacific Rim when the Kaiju breaks through the Australian wall "like it was nothing." The Germans simply rolled around the Maginot Line. No wall is proof against firepower. Walls would only make sense if your giants are brainless animals with no problem-solving skills. Are they? $\endgroup$ – JBH Jan 20 at 6:33

When building a wall you have to consider the following:

  • What is the inside and what is the outside
  • Is the wall to keep the inside in or the outside out

Humans have built walls for millenia, once upon a time we fenced off small areas to keep the wildlife out. As time has gone on our walls have expanded, now they're more often to keep the wildlife in.

Is there really a threat out there, is the great city wall more to keep the people in the city than to keep the enemy out? If not, then consider that in the European medieval age, most cities were walled. China on the other hand, tried to wall in the whole country. We like walls.

Walls are a universal part of human civilisation

When under threat we build walls, it's such a common theme that it could almost be considered a reflex. People still try to build walls when everyone else says walls aren't a valid solution. We really like walls. The humans that survived the giants' attacks are the ones that built walls high enough, and strong enough, that they worked.

Getting everyone into one walled city is hard

If the walls worked in one place, they'll work in another. It might be too dangerous to cross the badlands, so all the known humans are in one city, but that can't exclude other cities that are merely unknown. Remember that a large percentage of the planet's land area was unknown to anyone other than the local inhabitants until relatively recently. People have to be travelling relatively freely and safely for other cities to be known.

  • $\begingroup$ I really like the idea that now the walls are there to keep people inside. But the premise of the question is that there is a danger outside. And that danger are not other humans (which is the case in the medieval age walls). $\endgroup$ – Masclins Jan 14 at 9:44
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    $\begingroup$ @Masclins, my main point is that humans build defensive walls, it's so common when under threat that you could consider it almost a reflex. The surviving humans are the ones who built walls that worked. $\endgroup$ – Separatrix Jan 14 at 10:14

I would suggest it being a matter of coevolution. Early humans had a natural predator (e.g. early giants), and as humans developed methods of keeping the giants out, the predators best suited to overcome these obstacles would prosper, helping their race become better suited to overcoming these obstacles.

It wouldn't have to be giants, and as long as these predators do not die out from starvation they might specialise in overcoming these walls. This could be motivated through the knowledge that once the initial obstacle is overcome, a lavish feast free for all would be available (since humanity has prospered without the predators having eaten them).

I hope this provides some inspiration.


From a comment of mine (since having just one wall would eliminate the need for progression due to killing everyone once overcome):

[...] there could be multiple 'colonies', leading to a stronger progression. Alternatively there may be a castle-like 'greater-settlement' for the poor with multiple layers of protection. The outermost would feed the giants and allow the inner rings to observe and improve, perhaps.

If you segment your cities tightly enough, the predators may leave the conquered zone since there is no longer any food available, allowing the humans to gradually rebuild the broken walls when the giants are distracted/sleeping.

  • $\begingroup$ Surely then the surviving giants would be the ones who had bested the walls, so humanity wouldn’t be safe within. $\endgroup$ – Joe Bloggs Jan 14 at 10:29
  • $\begingroup$ @JoeBloggs I agree, but there could be multiple 'colonies', leading to a stronger progression. Alternatively there may be a castle-like 'greater-settlement' for the poor with multiple layers of protection. The outermost would feed the giants and allow the inner rings to observe and improve, perhaps. $\endgroup$ – A Lambent Eye Jan 14 at 11:25
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    $\begingroup$ The layered city idea is called a curtain wall and was used in castle designs - actually its the premise for the cities in Attack on Titan $\endgroup$ – JGreenwell Jan 14 at 14:12
  • $\begingroup$ @JGreenwell That was precisely what I meant, thank you. $\endgroup$ – A Lambent Eye Jan 14 at 14:13
  • $\begingroup$ I will add (as a thought I have when watching that anime - which I admit is not much) is that the original designs included portioning the city with additional checkpoints and gates (so instead of 3 circle portions you ended up with multiple triangles due to gates and checkpoints which block or trap intruders) - this was really hard to build but extremely effective - and once outer walls are built you can make these improvements safely $\endgroup$ – JGreenwell Jan 15 at 1:11

IMHO the simple answer is to have civilization rise and flourish and develop for centuries and millennia. Then the outside treat arises from somewhere outside.

Maybe a fleet of spaceships lands and invades. Maybe an astronaut returns infected by alien organisms, turns into a mother monster, and spawns hordes of monsters.

Maybe a new and improved sailing ship design allows the discovery of other continents. In which case perhaps the explorers capture a few baby monsters and bring them home and the baby monsters grow up, escape, and reproduce, infesting the continent with monsters.

Maybe the explorers find a "lost world" and bring back a few dinosaur eggs that hatch.

Or maybe there are civilizations on both continents and the explorers form colonies on the new continent and expand, conquering some of the natives, and other native societies build walls to keep the newcomers out.

And it is possible that more than one species of intelligent beings might exist on your planet.

Most humans assume that Homo sapiens is the only species of people or intelligent beings on Earth, and has been for many thousands of years since other hominid species became extinct.

But among mammals alone, there are about 90 other species of primates, proboscideans, and cetaceans with very large brains that might potentially be intelligent enough to be classified as people, and thus it is possible that the number of intelligent species currently on Earth might be higher than one and possibly as high as ninety.

The possibility that proboscideans might possibly be as intelligent as humans is especially interesting because proboscideans are land animals and much more widespread than apes, despite their range shaving shrunk drastically in recent centuries. And up until the end of the last glacial period 13,000 years ago, proboscideans lived on every continent settled by humans except Australia. In addition to the three surviving proboscidean species there were at least 15 more species 13,000 years ago that have become extinct since then, with human hunting being blamed by many as a contributing factor.

Since humans are also blamed by some for causing or contributing to the extinction of other hominid species, the possibility of violent conflicts between various groups belonging to different species of intelligent beings on the same planet seems fairly plausible. If some of those groups are civilized, building walls might be one thing that they do because of those conflicts.

And even within a single species, different countries, tribes, and groups can fight wars, such as happened many times on Earth. Thus civilizations in both the Old World and the New World often built defensive walls.

And perhaps the history of Eurasia might be instructive. There were many defensive walls built around towns and cities, and sometimes around larger areas. And then, Genghis Khan united the Mongol tribes and set out to conquer the world, and the Mongols conquered the largest contiguous land empire in history, and massacred many millions of people in the process.

It may be noted that Egypt under the Mamluk sultans managed to defeat and hold off the Mongols in Syria. But if the Egyptians had been less successful they might have abandoned Syria and built a short defensive wall in the narrowest part of the Sinai peninsula. That would have made the entire African continent defended from the Mongols by a wall in the Sinai.

The Song Dynasty of China never ruled the northernmost parts of China and so probably never defended or maintained the Great Wall. But they did construct a forested belt to defend against the Liao dynasty of the horse riding Khitan, who in turn built long sections of northern walls. During the Song-Jurchen alliance against the Liao of 1115-1125, the Song removed the defensive forest, and then the Jin Dynasty of the Jurchen attacked and conquered northern China in 1127.

The Jurchen saw no need to recreate the forest barrier in the middle of their land, But they did build two long stretches of the Great Wall of China as a defense against the Mongols. When the Mongols conquered the Jin Dynasty of northern China from 1211-1234 they preferred to go around walls and fortifications whenever possible, or persuade the disaffected Khitan garrisons to let them pass through.

If the Liao and Jin dynasties had maintained, rebuilt, and added to the Great Walls enough to make them impregnable and impossible to go around, and if the Jin had kept loyal garrisons on the walls, they might have kept the Mongols out of China and saved tens of millions of lives.

Even though the Mongols had the typical nomadic dislike for sedentary peoples, and even though they massacred tens of millions of people, they didn't try to exterminate all civilized and sedentary people.

In a fictional setting there could be an even more terrifying version of the Mongols, combining the worst features of Nazis and Mongols, that do exterminate every single civilized person they can catch. In such a setting, civilization can only exist where those ultra Mongols cannot reach, and perhaps the only way to hold those ultra Mongols off is to build walls they cannot penetrate. Thus the only civilizations in that world would exist behind defensive walls.

It may be noted that civilized societies build many walls for reasons unrelated to military defense.

There is the Inland Customs Line in British India, for example.


Or the Dingo Fence of Australia:


So possibly the civilization had its walled cities and its farms and pastures all surrounded by a great wall, and outside there are ravenous predators that would eat all the flocks if they got inside the wall, and/or vast herds of large herbivores that would eat up all the crops and the pastures if they could get inside the wall.

And possibly if the vast buffalo-like herds of herbivores got inside the great wall and stampeded when the people tried to chase them out they would knock down houses and barns and orchids and make a terrible mess of things.

Or possibly there are terrible weeds outside the wall that only spread though their roots, that would choke out the food plants if they got inside the walls.

So possibly the civilized people would be in danger of starving to death without their food sources without their great wall, but would not be in danger of being massacred by human enemies combining the worst features of the Nazis and the Mongols or being eaten by man-eating monsters. There are many different kinds of danger.


If we're excluding any supernatural evil such as giants and alike, the first thing that comes to mind is decease or radiation. Magical/futuristicly technological or even regular walls (in case of a decease that spreads through blood or bodily contact, for example) would ensure that at least some survive, thus making such measure completely logical. Plus it gives the citizens themselves an additional motivation for both staying within the walls and trying to ward off any potential intruders. And in case the government oversaw the issue and planned to resort to such measure in advance, they would certainly have the time to construct everything as well.


The humans didn't build the walls, the walls were built around them.

Some other (potentially ancient/forgotten/extinct) civilisation build the walls around the emerging human civilisation. The humans don't know this / have forgotten it and assume their ancestors built it. There a multiple possible reasons for why the walls were built:

  • Humans are funny pets. The other civilisation liked watching them.
  • The outside is actually dangerous for humans and whoever built the walls wanted to preserve the emerging (sapient) human civilisation, but their ethics prevent them from doing anything else.
    I would imagine that if we found life on mars today; this is one of the most likely ways we would deal with it.
  • Whoever built the walls saw humanities potential ... for destruction. And to keep the rest of the world safe they built walls around the humans.

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