I am imagining a water covered planet. There could be a few pieces of land scattered here and there, but >99% of the planet's surface is water. There are various ecosystems and biospheres where a race of super intelligent octopus-like creatures have risen the evolutionary ladder. The steps it took to get there don't need to be explained unless you feel like it.

These creatures have pretty much the same physical and emotional needs and are social creatures just like us, only octopus shaped (meaning soft, invertebrate with extremely dexterous tentacles (I guess 8, but can be more or less)). Assuming that they have evolved to be technologically equal to present day humans AND that on a whole they decided that permanent shelters where a good idea, how would their urban centers differ from ours? Mainly, how would the construction of the buildings differ? Would it be more efficient to anchor them to the sea floor or to a floating buoy? What would be a possible building material (I'm unsure on how pouring concrete underwater works)?

Bonus question: In this world, suppose an earthling human felt like taking a vacation in one of this underwater world's best 5 starfish hotels (He is the first non-aquatic being to visit this planet). What should he pack (other than scuba gear and extra oxygen tanks) to have a great holiday full of high-jinx?

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    $\begingroup$ I suggest you read the Rama tetralogy, by Arthur C. Clarke. He introduces a race of alien "octospiders" - which is kinda like what you describe here. On the third and fourth books he describes their society in detail. $\endgroup$ Aug 11, 2016 at 20:48
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    $\begingroup$ Aside from being in the same world your bonus question is not related to the octopus-city question, so I suggest editing it out here and asking it separately. (You'll probably need some more constraints, though.) $\endgroup$ Aug 12, 2016 at 2:41
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    $\begingroup$ @Renan Books 2-4 of Rama were probably written by Clarke's collaborator Gentry Lee. I like Clarke's writing, but I sadly found the Clarke & Lee books almost unreadable. But the 'octospiders' sound like a fun concept. $\endgroup$
    – a4android
    Aug 12, 2016 at 13:34
  • $\begingroup$ Related, not duplicate: worldbuilding.stackexchange.com/q/30749/10851 $\endgroup$
    – cobaltduck
    Aug 12, 2016 at 14:10
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    $\begingroup$ Instead of 'building' buildings, they might set up a frame and let coral grow around it to finish the structure. $\endgroup$ Aug 12, 2016 at 16:28

3 Answers 3


One way their urban centres would differ is how a city is vertically laid out. For us the only way to the top floor of a skyscraper is to climb the stairs or go up in the lift. However your octopus can just swim up to any floor it pleases. So there will be entrances and exits for the entire height of a building. (Your human visitor will need a 3 dimensional map or he'll get lost).

Windows and doors may be pretty much interchangeable. A door is just a window with the shutters closed.

Other vertical things to think about: wave base and light.

Wave base is how deep in the water the action of waves happens. Above it, your building will be battered by the waves as they pass overhead. Below it, you are out of reach of the waves, so your building will be unaffected.

Therefore, buildings which you want to be safe from the biggest waves (a school or hospital, for instance) will be built at depth. Poor folks may have their homes in the shallows, where they are always being torn to shreds by storms.

On the other hand, light decreases with depth. That hospital may be safe, but it will also have much less light coming in the windows. The octopus folk will need artificial lights and/or will have eyes adapted to the dim light of the depths.

Our ocean is full of reef-building animals: various corals and molluscs. The octopuses can exploit these to make their homes - rather like planting hedges. However, they'll only be able to do that in environments which suit the reef-builders. Corals need shallow, warm water which is low in nutrients, for instance. There may be regional differences in construction because of this. UK octopuses use mussels and oysters, Australian octopuses use coral.

However, corals, mussels etc are very slow growing compared to how fast a human can make a log cabin or get a bricklayer to build a house. The octopuses may need to weave houses out of kelp, or use mussel byssus thread to cement rocks together. Barnacles also have a very strong cement, so they could use that too. Both of these have evolved to set underwater.

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    $\begingroup$ +1 for mentioning the wave base. The ocean floor, below areas with a large amount of wave action, can experience the force of four hurricanes a day. $\endgroup$ Aug 13, 2016 at 22:35

The steps it took to get [to civilization] don't need to be explained unless you feel like it.

Since Caleb has already addressed this, I will skip it.

How would their urban centers be different from ours?

Like us, urban centers would be hubs for trading. They would buy and sell goods and services, such as: food, fish-farming supplies (feed, rope, cages, traps, etc.), materials for habitat, seeds or baby plants, information pertaining to travel, and education. Importantly, it would be a center for mating. There would be extremely popular nurseries open for the millions of eggs laid each month. The rich may choose to house all of their eggs, whereas the poor may only be able to house three or four (and so have a difficult process choosing which eggs to nurse).

'Buildings' may be much more loosely defined than ours. An urban center very well may be a healthy coral reef. There could be floating travel platforms for long-distance movements along currents. Imagine a very large, cloth, thrown into the ocean with pockets sewn into it. Some pockets contain air (to maintain buoyancy). The rest are used at discretion. Here, octopi may attach cages to bring fish for eating with, pouches to store feed and small objects, and pouches to sleep in.

An important question to ask yourself is: do my octopi have beasts of burden? Because electricity is difficult to harness underwater, the presence (or lack thereof) of beasts of burden may be a defining point in this civilization. (Keep in mind that some historians say that the lack of beasts is what kept the South American ancient civilizations comparatively limited.)


So I want to start off by asking how well you considered the idea of underwater creatures using electricity. I don't think that it is actually possible to generate and use electricity underwater unless you previously developed insulation techniques. The extreme conductivity of the water makes any early experimentation almost 100% lethal. But now that I have that off my chest, I will continue by answering as much as I can.

The big stumbling block in the development of a civilization is probably the creation of manufactured metal goods. After that, everything is easier. Thing is, octopi don't have bones. And bones are preferable for using human-style tools. So The octopi will probably need to make small tools with multiple purposes. As I said, though, processing metals for tools is very important, so they will need forges. Now, you can't easily build a fire underwater, so I suggest making a forge, which would be a centrepiece for this kind of civilization, on top of a volcanic vent. This kind of thing would certainly be anchored.

Another highly important building is a place for octopi to sleep. I imagine that with the harder life the octopi are doomed to have, materials and food are generally shared, so living spaces can be confined to a place to sleep. But since octopi are invertebrates, all you need is a large object with lots of little holes, some bigger to house families or mating couples. I think a basic chunk of coral would do just fine. A reef would also provide food, so we have that problem solved as well.

Having very little waste and with pooping in the ocean being no problem, no sanitation department is needed. Neither is transportation for distances of under a few miles, as swimming outdistances most vehicles quite efficiently.

Cultivation and farming underwater looks a lot like it does above water. Scared away predators to the farm fish, cage or otherwise enclose said fish, let kelp grow and then harvest it. As for distribution, rotting is slower in saltwater, so a hollowed out boulder or some such should do, plus you can supplement your diet with passerby fishes.

Transportation long distance seems somewhat important. Since buoys are moved by both current and wind they could make excellent vehicles when properly piloted.

As for building materials, I would say to just use coral and rock. "The elements" are a lot less harsh on your stuff down here, so specifically manufactured building materials or cement are unnecessary.

Another thing going for our octopus friends is their squishiness. Doors can be only centimeters across , rooms incredibly small as the octopi don't really need much as they are, and of course safety measures are almost irrelevant, considering how easy it is to rebuild and how hardy octopi happen to be.

So while I know this isn't the question, I don't think that without fire, wood, or electricity, octopi could actually reach human levels of technology. But the nice thing is that their infrastructure would be pretty simple, as they are already a wonderful evolutionary model.

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    $\begingroup$ Sanitation may be more of a problem than expected. Particularly if surrounding water is contaminated by waste from a large number of octopuses gathered together in close proximity. Perhaps, this could be solved by locating octopus cities in ocean currents to keep them clean and comfortable. Congratulations on mentioning squishiness. My first thought & you got there first. Well done. it's a nice answer. $\endgroup$
    – a4android
    Aug 12, 2016 at 9:00

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