Six thousand years ago, magic users from Earth managed to create a portal between Earth and another planet, far far away. This planet is Earth-like but developed no life forms whatsoever.

Its new population started to terraform it, using both magic and biology. But even with magic, the process is expected to last at least ten thousand years more, and the planet still doesn't have a breathable atmosphere.

The City


The wizard planet's biggest city, and capital, was built on a plateau. The plateau is bordered on one side by a massive mountain range, and by the sea on the other.

A river, taking its source in the mountains, runs across the plateau, just next to the city.

space wizard city geography

City plan

A network of canals supplies river-water to the city and evacuate the excess water toward the sea.

The city is made of thousands of small blocks, hexagon-shaped and separated by large canals. Those canals are filled with algae, producing most of the city oxygen.

A spell maintains a tiny Earth-style atmosphere over the city. It protects it from solar radiations and prevents oxygen from escaping too much.

On the outskirts of town, this spell is a bit unstable. Sudden gusts of wind coming from outside the city can turn the air unbreathable for a few minutes at a time. That's why these areas are only used for tree plantations, and people going there have to bring special equipment with them.

Space wizard city plan


From inside the city :

City blocks are multipurpose, they can support a mix of housings, vertical gardens, hospitals, markets, insect farms, schools, factories, etc. The city itself produce most of what its population needs.

  • Vertical gardens (buildings used as multistory greenhouses) -> Fruits, vegetables, mushrooms and oxygen.

  • Rooftops gardens (with beehives) & window boxes -> Flowers, wax and honey.

  • Insect farms -> Protein paste and silk.

  • Floating duck farms (they feed directly from the canals) -> Meat, eggs, feathers and leather.

  • Rabbits (kept in hutches inside houses and fed with peels and leftovers) -> Meat, fur and leather.

  • Tree plantations -> Bamboo, rubber, arabic gum, fruits, nuts, cork, oxygen and wood (in relatively small quantities).

  • Canals -> Oxygen and bioluminescent micro-algae, illuminating the canals at night and put in glass jars to light storefronts and houses.

  • River -> Fresh water and energy to power mills.

From outside the city :

Hundreds of stations are scattered around the planet and are homes to a total of more than a million habitants. Stations can take many forms, from small towns to hovering mobile factories. Their primary functions are to grow algae, jellyfish and other stuff, then inject those in the oceans, and to plant lichen and grass on the most hospitable lands. They also produce useful resources.

  • Sea-side stations (practice pisciculture) -> Salt, dried sea food and algae (mainly spirulina).

  • Mining stations -> Metals, gems and stone.

  • Planting stations -> Lichens and herbs, used to make dyes and medicine.

The exchanges between stations and the capital city are made using flat-bottomed "boats", made of metal and able to hover a few meters above any body of water.

From Earth

The inter-galactic portal is still active.
It's only used to do "educational travels", allowing wizard spies to study the technological progress made on Earth, to "save" gifted babies born from Earthlings and to dump the few non-wizard babies born on the wizard planet.

The portal is a well-guarded secret and can't be used for large-scale imports, or even to bring back objects bigger than a backpack.


In this universe, magic can't be used to create matter or achieve nuclear transmutation.

However, it can produce heat and light, accelerate the development of life forms, make things hover, improve physical abilities, power sentient automatons, create large-scale spells, etc.

Magic is not an infinite resource, and the vast majority of the population uses it only for the bare necessities, like heating food and charging magic batteries then sold to businesses, rich families or public institutions.

City-design problems

I'd like the space wizards capital city to have between one and two million habitants and to stay sustainable for the next ten thousand years.

A few minor problems :

  • The city doesn't produce cereals (Maybe legumes can take their place?), or milk.

  • The only source of leather is duck and rabbit skins.

  • The only available fabric is silk (And maybe some kind of rough fabric made of bamboo fiber).

  • I'm not sure white paper and cardboard can be easily produced (without using chemicals) from bamboo and/or algae.

  • The wood production is small relatively to the population, small enough so that lighting a fire is a luxury (But for most of its uses, wood can be replaced with bamboo, metal or stone, and in this world magic can be used to produce heat).

  • I'm not sure if the city needs to have electricity. Also I don't know what would be the most effective way to produce it (water mills ? wind turbines ? centrals using magic heating instead of charcoal ? ), and how they would manufacture all the equipment needed without the use of plastic, limited supplies of rubber and no modern manufacturing tools.

Those problems are not unsurmountable, but I'm afraid I missed bigger flaws in this city design.

There are certainly important resources I forgot to provide to the city, or some potential disaster I didn't think about.
The "important resources" may not be obvious (like food, water or light) but something a million-habitants city will need to keep existing for millenias.

Note : I'm not looking for methods to accelerate terraforming.

Question :

Is this city sustainable and why ?

Some useless information (it may interest someone)

I decided that the city couldn't sustain farming bigger animals (like cows, horses or pigs), but it could change if necessary.

My story starts 6 000 years after the opening of the portal, and 10 000 years before the air of the planet becomes breathable.

Here is a somewhat related question I asked a while ago

The protagonist of the story is a "normal" human, born in an aristocratic wizard family and dumped on Earth by his/her (I still haven't decided) parents.
Years later he/she is contacted by one of his/her siblings and returns to the wizard planet, only to discover that the only reason for this return is so their siblings could perform a spell.
This spell is supposed to allow them to locate their mother, who has been missing for months. It necessitates 7 children of the missing person to work, that's why they needed to get their ugly duckling back from Earth.
They don't officially accept our protagonist back in the family but disguise him/her as a servant, which allow him/her to explore the city discreetly.

The story is mostly about the protagonist running around, trying to elucidate mysterious things happening around the city and looking for a place in wizard society.

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    $\begingroup$ You might want to rethink rabbit skins for leather. They just aren't thick enough. $\endgroup$ Commented Apr 10, 2016 at 18:24
  • $\begingroup$ @WhatRoughBeast Do you think the city can't keep functioning without thick leather ? $\endgroup$ Commented Apr 10, 2016 at 19:40
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    $\begingroup$ I think pretty much any goats could live in a garden, just not a whole lot. What I'm saying is no need to limit yourself to just one kind. Although I think a few goats would go a long way to helping your city. $\endgroup$ Commented Apr 10, 2016 at 21:56
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    $\begingroup$ Fabric:: en.wikipedia.org/wiki/Bamboo_textile $\endgroup$ Commented Apr 11, 2016 at 0:44
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    $\begingroup$ Bamboo fiber clothing does exist currently, and is incredibly soft and comfortable... Just fyi :) $\endgroup$
    – ASH-Aisyah
    Commented Apr 11, 2016 at 7:16

4 Answers 4


A basic ecological fact: for the next several hundred million years, the oceans will be uninhabitable to almost all animals. That includes jellyfish, and whatever pisciculture you had in mind. With no oxygen in the atmosphere, there is no oxygen dissolved in the oceans, either. Until the algae and other plant life have conquered the ocean (and this requires an enormous variety of both plants and bacteria), oxygen levels will remain extremely low. Once the oceans are busy cranking out oxygen, only then can the rocks begin to oxidize, and with a world full of rock waiting to be assimilated, this is going to take some time. This actually happened with the Earth - see The Great Oxygenation Event Only once the Banded Iron formations (or this world's equivalent) have been laid down will the atmospheric oxygen levels start supporting higher life. There are a few animals which are close to anaerobic, and can live at very low dissolved oxygen levels, but not many.

If you want to finesse this time requirement, feel free. Yours is a magic kingdom, after all.

So, let's say you've got these stations, "Stations ... primary functions are to grow algae, jellyfish and other stuff, then inject those in the oceans". You should realize that, if the oceans are colonizable, once you seed them with even a small amount of (let's say) algae, adding more simply won't help. It's the wheat/checkerboard problem - if the algae are at all successful, they will expand exponentially, and after a few years adding more from the stations will be just a drop in the bucket. What the stations might do is to provide more and more species (imported from Earth, obviously), with the goal being to increase biodiversity. Ocean currents will disperse the algae in (relatively speaking) a very short time. Once oxygen levels are up, it will only take a few loads of animals to begin explosive growth rates on that front, too, although the initial effects will probably be wild population swings until the ecosystems reach some sort of (possibly dynamic) equilibrium.

As shown, your canals are not canals in the usual sense. The Venetian canals, for instance, are part of a lagoon, not a river. The difference is that canals are part of an essentially stagnant body of water, while your "canals" will have appreciable flow rates. This means that you can't grow algae and such, since they will be swept out to sea. Rooted water plants may be a possibility, but be aware that these usually require soil to root in (not wet rocks) and this will require considerable preparatory work to produce.

EDIT - I suspect you're grossly underestimating the amount of plants and algae you need to support your city. Here, for instance is a paper talking about an improved algal system, and note that it suggests that such a system would provide the oxygen for one person with a power input of 30 kW. That's continuous. Figure that sunlight is about 1 kW/$m^2$ for 6 hours per day, and you need about 40 square meters of pond/lagoon per person. Note that going to vertical gardens won't help - the limiting factor is solar energy. For 2 million people, you'll need about 80 million square meters of horizontal surface, or 80 square kilometers.

  • $\begingroup$ Could algae be grown behind some form of dam? $\endgroup$ Commented Apr 11, 2016 at 9:37
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    $\begingroup$ Sure. Especially a series of small dams distributed throughout the canal network. Anything to cut down the flow rate. In fact, you want to maximize the area of these shallow ponds in order to get enough oxygen. Of course, now you have to worry about sediment buildup, among other things. Please see the edit. $\endgroup$ Commented Apr 11, 2016 at 14:48
  • $\begingroup$ In my setting, the city casts a spell on the canals to strongly increase the growth rate of algae (the same spell is used in the stations on the stuff they're releasing in the oceans), and the whole river doesn't flow trhough the canals, only a small part of it (so the flow rates wont be very high). Point taken, I think I'll make all stations mobile, add to their duties the magical acceleration of rocks oxydization, and have them change the "batch" they're cultivating (basically they take new samples from different parts of Earth's oceans) regulary, I'll also increase the canal/people ratio. $\endgroup$ Commented Apr 18, 2016 at 8:14

I think your city could be sustainable with a few tweaks.

For plant and animal resources, you could have your wizards introduce plants and animals that can exist in the planets atmosphere. These plants and animals could either be created by magic, or brought in from another planet (with another portal), or taken from Earth and manipulated in some way.

Perhaps these plants and animals cannot breathe our atmosphere, and they avoid the city and stations (but with the potential for attacks on your boats as they travel between the city and the stations).

If the planet could sustain its own ecology, most of your resource issues would be solved.

As for an energy source for electricity - maybe consider geothermal power, its potentially limitless and clean, and would work on the planet regardless of its current state. Perhaps you could have some Iceland-style hot springs inside your city's hexagon network. Or you could use the river itself as a source of hydro-power (I assume a station would be built to operate and maintain the hydro power station on the rivers banks).

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    $\begingroup$ I don't think so--the atmosphere doesn't have oxygen, what do you modify the animal to to allow it to survive? (And why don't they modify themselves that way??) $\endgroup$ Commented Apr 11, 2016 at 0:46
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    $\begingroup$ Not modifying themselves? Maybe they want to stay human. Modifying "dump" farm animals may be seen as acceptable while a modification of the humanity may not. $\endgroup$
    – TomTom
    Commented Apr 12, 2016 at 8:41

A few problems you may have missed

Medicine - What do the wizards do if they get ill? Magic it away?

Contraceptives - If these wizards have casual sex they will end up with a lot of babies to dump and people may get suspicious.

Transport - How do you get to the outposts? You may have mentioned this and I missed it.

Criminals - What do they do with criminals? Prison? Death penalty?

Drink/Drugs - Do wizards drink alcohol, I guess they could drink femented algae or something.

Rubbish removal - Is it just thrown through the portal because 1 million people will produce more than 1 backpacks worth of rubbish.

Dead bodies - Dumping dead through the portal is not a good idea. And throwing them in the sea seems harsh.


Overall I think that your society would be sustainable if the wizards impose a few rules:

All rubbish must be reused or recycled as much as possible.

Only take people from Earth who don't drink or take recreational drugs. With no drink or drugs in your new world the next generation won't have even heard of drink and drugs.

Casual sex is banned. See my section on crime for the punishment.

Transport- Small scale, temporary atmospheres around boats on the river. For land travel you would need either some form of fuel for cars or as the wind seems quite powerful you could use ailing carts or goat pulled carts.

All dead must be cremated so that there remains can be kept hygienically or put through the portal without suspicion.


Criminals breaking minor laws (theft, casual sex etc) should have to do community service maybe on one of the far flung outposts without the city comforts. Criminals breaking major laws should be killed, cremated and returned to Earth.

  • $\begingroup$ They only dump non-magical babies, but that's a good point I'll add a contraceptive. For medecine, I don't expect them to have access to modern day western medecine. As for rubbish removal, remember that they don't have plastic or any kind of mass-produced goods. I just assumed they could dump whatever few non-recyclable rubbish they'll end up with in the sea. $\endgroup$ Commented Apr 10, 2016 at 21:36
  • $\begingroup$ @SpaceLizard I think that adding in contraceptives will annoy quite a few readers. A better contraceptive is called self control. Again, drugs/alcohol. Not a necessary at all, and while these are a lot more difficult to get rid of, it can easily be done without. $\endgroup$ Commented Apr 10, 2016 at 21:49
  • $\begingroup$ @XandarTheZenon I don't have readers yet, I've been writting for fun for years now. As for the mention of contraceptive anoying people, even if people read my stuff I don't think they would have weird reactions like that about this subject (I write in French, so my potential readership is limited). $\endgroup$ Commented Apr 10, 2016 at 22:03
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    $\begingroup$ @XandarTheZenon Well, for many teenagers that is the sole purpose of their life. $\endgroup$ Commented Apr 11, 2016 at 14:35
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    $\begingroup$ @XandarTheZenon I think you must be asexual or have some major religious issues. You do not understand human nature! And knowing people that haven't had children doesn't mean they haven't had sex. 30 years ago we chose the childfree path--doesn't mean we haven't had sex. $\endgroup$ Commented Apr 11, 2016 at 19:19

Strictly speaking, it may be sustainable, but is it economically advantageous? I doubt that.

People don't just colonize for no reason. Europeans colonize to find spice and land (for agriculture, desert doesn't count). Space colonies in real life may have exported solar power, mined rocks, Helium-3, etc.

Your Earth isn't in danger, there is no resource that cannot be efficiently produced on Earth, etc. So, colonizing that planet would be hard work for no gain.

Your planet should leave the portal wide open, because food is more efficiently produced on Earth while you should think what is so special about this planet so mages want to live here. It can be free mana, or the fact that the planet is (initially) barren plus the star is brighter here, you can build massive solar panels here.


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