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Comment by Cthulhu_ | Hacker News Reader

> You can't wall all the fields but you can wall the village.

An interesting take on this is depicted in Attack on Titan, where they do in fact wall all the fields - the city (I don't remember if it's like the last vestige of humanity or whatever) is surrounded in concentric ring walls, the outer one which contains villages and farmland having a circumference of about 3000 kilometers for an internal area of 723,822 km², making its area just a bit smaller than Zambia and Chile.

Of course, a 3000 kilometer, 50 meter tall wall is ridiculous. But then again the great wall of China is 21.000 kilometers long. I believe there's more info about the walls and their construction in the source.

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Ballpark figures based on the ram earth construction for TGE vs AOT would have the AOT wall be 5-10x the volume & mass of the TGW. The issue is labor — the Great Wall probably represents 20–100 million ma years of labor. The AoT wall probably has at most 100k man years of labor it could've pulled from. That'd mean it's labor-mass ratio is off by 1000–10000x.

This gets into spoiler territory, but the walls in Attack on Titan weren't made with human labor. The first hint that something funky is going on was at the end of the first season finale, but we don't get the full story about the walls until much later.

It also was built when Marley was still very much a massive empire. So it wasn't limited to the manpower inside the walls. This is clear from how many of it's actual construction materials were used.

Enclosing a settlement gets easier as it gets larger. The amount of work is proportional to the perimeter, while the number of people to do the work is proportional to the area. The area is proportional to the square of the perimeter, so the work per person is inversely proportional to the length of the wall.

That only applies if you have the people. The limit of village population is the ability to grow enough food to feed it withing walking distance of the gate. And so your village cannot get a large enough population to overcome this.

Cities can only pull off a large population if there are a lot of villages growing surplus food (which is not what the village wants - in the medieval world cities were not making luxury goods farmers wanted so farmers would want to work less), and cities needed good bulk transport for all that food. Rome was a massive city in the day with just over a million people - today that is considered a tiny city and there are many much bigger.

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