For a DnD campaign, I'm designing a setting with steampunkish tech level, as well as magic used to explain tech accomplishments not possible with real world physics. Almost all settlements in this world are "moving cities", powered by extensive clockwork mechanisms, that gain the majority of their resources through either moving to a new area and harvesting the wood/coal/etc that can be naturally found there, or through stealing resources from other, smaller, cities.

My question for you all is: What sort of population numbers would be reasonable for the Large and Medium cities of the world?

For context, the world will contain the following city sizes:

  • Large city - primarily fully predatory, taking resources from medium sized and small cities. Constantly in motion.
  • Medium cities - some economies and resource acquisition from trade with other cities or harvest of the surrounding areas, but also predication on smaller cities.
  • Small city - primarily gain resources through harvesting from the natural resources around them. These are probably going to be no more than 100 people.
  • Sedentary settlement - extremely small, less than 10 people. Primarily hiding from the cities to avoid being preyed on, but rarely trading with some of the cities.

I'm attempting to set this up roughly like a food ecosystem web, except with cities rather than animals. Additionally, leaders of large cities have an agreement to attempt to preserve this system, so "harvest" of resources from prey cities is done in a way that doesn't completely cripple that city. Catch and release, basically.

Any help you all can give me would be vastly appreciated, thank you!

I am drawing inspiration from the Mortal Engines book and movie setting, if this helps explain what I mean by "moving city".

(Edit: I'm relatively new to Stack Exchange, if I've messed up any other rules or norms for the community please let me know and I'll edit to fix)

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    $\begingroup$ For all this information you should look at the illustrated guide to mortal engines. Philip Revee goes into great deals about the workings of the cities Godshawk engines which are omnivorous and can burn wood, oil, coal and gas. I worked out that a city with a population of $\endgroup$ Oct 28, 2021 at 21:02
  • $\begingroup$ I’m sorry i am also new. I joined yesterday. $\endgroup$ Oct 28, 2021 at 21:08
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    $\begingroup$ I've never heard of 100 people referred as a small city before. $\endgroup$
    – sphennings
    Oct 28, 2021 at 21:08
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    $\begingroup$ @JoinJBHonCodidact, apologies about the rules, I'll edit my post to clarify what my primary question is. And regarding Reeve's stuff - I'm using his work for inspiration, but I don't actually have the books, or any convenient way to acquire them, which is why I was hoping I could ask folks here who know things about population numbers and similar regarding how this could realistically work $\endgroup$
    – jayb1rd
    Oct 28, 2021 at 23:43
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    $\begingroup$ Thank you for the help, everyone, I appreciate it! @ProjectApex, that's a really useful video $\endgroup$
    – jayb1rd
    Oct 30, 2021 at 22:34

1 Answer 1


To give some background perspective, let's look at the world's largest floating city - the Symphony of the Seas.

  1. SYMPHONY OF THE SEAS SIZE The Royal Caribbean Symphony of the Seas has a construction date of 2018 and a total size of 228,081 gross tons. The ship measures 1,188 feet (362 meters) in length and falls in line as number 1 among Royal Caribbean's 36 existing and former cruise ships. It’s included in Royal Caribbean’s Oasis Class. At full capacity, the Symphony of the Seas holds 7,718 passengers. That includes 5,518 cruise vacationers and 2,200 staff members. The Royal Caribbean Symphony of the Seas total number of staterooms is 2,745.

Symphony of the Seas Size & Stats Gross Tonnage: 228,081 GT Ship Length: 1,188 feet (362 meters) Beam: 137 feet (42 meters) Draft: 31 feet (9 meters) Max Speed: 25 mph (22 knots) Year Built: 2018 Years Served: 2018-Present Capacity: 5,518 passengers Crew Members: 2,200 Total on Board: 7,718 Total Staterooms: 2,745 Flagged Country: Ship Cost: $1,350 Million Status: active

This ship is so humongous, it would certainly be considered as a self-contained town, with all amenities typical of one. However, the living accommodations leave a lot to be desired, should one be spending their entire life on such a ship. It is so big it could carry the largest American aircraft carrier Gerald R. Ford inside of its confines and still have room for a corvette or two.

So if somehow you can get a ship of this size to operate on land under steam punk, it would seem that around 10.000 people would be an upper limit based on what we currently have on earth. Maybe cut the ship off at the waterline, put a flat bottom on it, and put mega huge wheel boogies under it. Something along the lines of:

July 31, 2008 Mine operators are increasingly adopting larger equipment to lower operating costs and a new class of ultra-large machinery is demanding bigger tyres. Earlier this week, Titan Tire shipped its first giant 63-inch off-the-road (OTR) tire and wheel assemblies. The tires, each measuring nearly 14 feet tall and weighing approximately 12,500 pounds, are being shipped to Canada’s oil sands for use in mining applications and Titan envisages a worldwide market of 900 tires a year.

  • $\begingroup$ That's very helpful, thank you! $\endgroup$
    – jayb1rd
    Oct 30, 2021 at 22:33

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