I have a city-state, bound to protect the evil, and the souls of the inhabitants are used to power that, and no one who enters the city can leave, so the outside world supplies it with food and supplies for free. It's been this way for a thousand years, starting with a largely high medieval technology, and they've managed to build up their technology to a roughly early 20th century level. There's about 100,000 people spread over 3.1 square kilometers.

Technology-wise, gunpowder and other explosives are generally unknown or nonexistent, as are fossil fuels. They have a steam-engine train (running on thyme, or jokes aside, vegetable oil) (or electricity?), photography (with color photos produced ala Prokudin-Gorsky), massive electro-mechanical computers for bureaucracy more than mathematics (complete police records are on a steel punched tape, and citizenship records are all on punched cards), and air conditioning for the hellish summers. Telephones and telegraphs are in limited use, due to the size of the city and efficient mail service. Automobiles are not in practical use, as the city wasn't designed for them and fuels aren't cheap. The city magic is spherical, and it stops egress by invisible wall against living matter; ballooning was briefly popular, with a number of fatalities, and a working airplane would be suicidal.

What other technologies would necessarily be available, that I would need to take into account or explain why they are nonexistent? I'm not asking about magic or magitech; there is magic, but not at an industrial scale.

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    $\begingroup$ This is an open ended brainstorming question of the sort not suitable for this site. We're here to answer specific questions, rather than engage in discussion about the potential consequences of the world you've built. $\endgroup$
    – sphennings
    Aug 17, 2022 at 16:00
  • $\begingroup$ I'm not asking about potential consequences; I'm asking about what technologies logically go along with the constraints given. $\endgroup$
    – prosfilaes
    Aug 17, 2022 at 16:40
  • $\begingroup$ One hundred thousand people growing sufficient food to avoid starvation 3.1 square kilometers (1.2 square miles, 766 acres) is already fairy-tale level magic. And don't forget that on the same 3.1 square kilometers they need to grow sheep for their wool and tallow, trees for their wood, and rapeseed for the oil to power their train. (Values to play with: rapeseed yeild is about 2 tonnes/hectare. 50% of that is oil. The calorific power of rapeseed oil is about 26 MJ/kg. What is the amount of coal equivalent to the rapeseed oil harvesed from 3 square kilometers?) $\endgroup$
    – AlexP
    Aug 17, 2022 at 16:51
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    $\begingroup$ (1) That should be edited into the question. (2) How do they pay for the food and materials? (3) Why would they buy rapeseed oil instead of coal? It is about 100 times mores expensive. (4) If they have contact with traders from outside the city, then they will surely have gunpowder, guncotton, rifles, pistols, revolvers, and other such amenities. $\endgroup$
    – AlexP
    Aug 17, 2022 at 17:13
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    $\begingroup$ Sounds interesting. Pneumatic tubes for transferring messages, other pneumatic devices. Vacuum tubes, glassblowing tech and plasmas for plasma lighting. Pressurized steam lines for heating in the winter, or other steam powered devices, with a centralized steam plant? Tesla cool and HV electrical devices for short range wireless power to reduce the number or wires between buildings? $\endgroup$
    – UVphoton
    Aug 17, 2022 at 19:14

2 Answers 2


The city is isolated and aged, the walls act as a one way valve when it comes to technical innovation. It is also hard to replace existing infrastructure and bureaucrats and the city planners are both pragmatic, resistant to change and have factions and political complexities that are arcane and not well understood - but once a technology is inserted they are resistant to other newer or perhaps cheaper technologies. A combination of if it is not broke, why fix it, and not invented here.

Since the talent valve is one way

  • like in our world there was an Edison vs Tesla like battle and in this case High Voltages and short range wireless transmission of power gets developed. Besides - there were starting to be wires hanging between buildings that were unsightly and so and so's son managed to electrocute himself on a wire. The Tesla coil like, or Van der Graaf generators on the streets might make people hair stand up once in while when the humidity is low, but that is harmless right? Besides any evacuated bulb of glass can then be a light source.

  • Transistors? - phawh who needs transistors our glass blowers and our vacuum tech allows us to make make very smal vacuum tubes, relays as well as microfluidic devices. Better yet, it keeps the urchins off the street, at least until they get too big. The bug boys learn a trade and an education while fixing the .... ???very large complicated computing device?? replacing valve and tube as necessary and cleaning out cobwebs and an occasional dead rat. Besides we can make all our own replacements and don't have to rely on those unreliable outsider. Centralized computation is better anyway why would anyone need a computer on their desk.

  • The steam plant - with it pipes under the street - might leak now and then but also heat to radiators when it is cold, but also large slow turbines to drive the looms and machinery. The steam plant yahoos are their own breed and might tend to go on strike occasionally and be a little crude walking around with their wrenches. The steam plant also keeps pneumatics pressurized.

  • Since there's not enough copper electric motors (too expensive) and and aversion for telephone wire, pneumatic tubes provide the mail system.


Why would they have significantly different technology than the outside world? The only way they're isolated is that people can't leave, so brilliant inventors might not flock to the city because they want the flexibility to leave, but with 100,000 inhabitants you're going to have people who can understand new technology that gets fed in from the outside world. Really, the only major constraint is size, and you already identified the problems with that (no airplanes, cars, etc). Everything else should be either learnable or importable from the outside world.

So if the rest of the world has 20th century technology, then this place should have the same tech, but nothing that takes up too much space. Similarly, if this city has a tech breakthrough, they'll probably export it to the outside world and it will propagate there.

Sanitation and water are two of the biggest problems, but they'd have figured them out water a long time ago but building lots of aqueducts into the city, and if they just toss their sewage outside the magic barrier it kills all the bacteria and parasites, so sanitation isn't a huge problem either.


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