I've searched through a lot of merpeople related questions on this site and didn't see anything that related particularly to me as most questions have to do with underwater combat or dwellings on the ground.

My species is a race of humanoid axolotls (that means legs and feet like people) who are perfectly capable of living on land. They do not have access to land though. Their cities are built on the trunks of massive "balloons" suspended in water. These balloons are full of oxygen with several inch thick membranes on each balloon. The spheres that contains the gas can range in size from a 3 meter to 20 meter diameter. The stalks reach up from the very bottom of the ocean, nearly 500 meters below, to from a few meters to a few feet below the water surface.

For extra clarity I'm going to restate what's so bad about the balloons getting popped. Cities are built out of a sort of underwater adobe and plastered on the trunks of these massive balloons midway or near the surface of the sea. If one were to pop it would soon fall over from the weight of the city on it's side. Obviously that's not good for my inhabitants or nearby balloon cities that might be hit.

So my question is: In the event of humans waging war on my peaceful civilization how would I protect against my balloons getting popped or from another form of attack from above?

The technology level is that of earth 1000 AD. My merpersons can swim at 20mph. Magic is rare if not nonexistent and most nearby countries have access to metallurgy and gunpowder and can launch projectiles at their enemies. The merfolk can tame things like dolphins but many do not have any creatures as they're difficult to provide for with the dense population zones around the balloons' stalks.

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    $\begingroup$ An exact opposite question was asked before (What would a medieval war against an aquatic race look like?). The answers there show that it'd be pretty hard for medieval humans to effectively attack merpeople unless they have powerful explosives. $\endgroup$ – default locale Feb 5 at 7:05
  • $\begingroup$ Hmm apparently my internet likes playing jokes on me. Sorry if you get mysterious nonexistent pings default. I have little to no control over if my messages send. $\endgroup$ – SlothsAndMe Feb 5 at 7:16
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    $\begingroup$ Can I ask as to why the humans are attacking the Mer race to begin with? Very little would be gained from sacking them, if they could even get the loot to begin with. If what you say about them being peaceful is true, then why are the humans attacking them unprovoked (it’s not like the humans would get land from killing them). The best bet would be diplomacy if the Mer offered trade deals and help at sea with non-hostile kingdoms they would fare better. unless religious hostility or racism is to play. but not or humans will act that way so diplomacy should still stand $\endgroup$ – Creed Arcon Feb 5 at 8:51
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    $\begingroup$ @CreedArcon The area where the nation is located is a prime location for trade routes. I understand that in many cases it would be better to just be diplomatic but sometimes people decide to do crazy things. And I'm just trying to figure out what they would do in response to an attack if there happens to be one in my world. $\endgroup$ – SlothsAndMe Feb 5 at 9:08
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    $\begingroup$ Again I have been misunderstood. Notice where it states that the balloons go from the bottom up to a few meters below the water surface. It would be extremely easy to access the bubbles of gas and destroy the cities. All it takes is a well placed sword and the whole entire thing comes toppling down @JBH $\endgroup$ – SlothsAndMe Feb 5 at 17:33

Giant Kelp forests around your settlements

have a massive kelp forest wall around your settlements were your Mer people hide traps that sunk or damage ships, launch surprise ambushes and conceal your balloons from the attackers. The traps could range from simple drift wood spikes to burning barrels from whale oil. Your Mer people can swim in and out of the kelp with ease and shoot at any intruders that come to close then board them. Use the shipwrecks to make more traps (and much needed steel and arms) and hang the dead from the ships masts as a warning to other would be foes. This is the Mer people’s water trespass and the locker will take you, the humans will learn to fear the deep.

  • $\begingroup$ This is a great answer! Extremely easy to execute and very efficient! $\endgroup$ – SlothsAndMe Feb 6 at 22:44
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    $\begingroup$ @SlothsAndMe well thank you. i hope it didn't come across as too hardcore for your peaceful Mer. but in times of war being outnumbered and outgunned one must be efficient, merciless and brutal in order to win. a guerilla fighter said it best "kill all they send and they will send no more" $\endgroup$ – Creed Arcon Feb 7 at 1:15

Swim beneath their ships and bore holes in them long before they're anywhere near your balloons, or even do it in their ports. 20mph is plenty of speed to accomplish this and ships are not cheap, they wouldn't lose many before deciding it wasn't worth the effort unless your cities are full of gold, and even then they have no way of fighting underwater.

The surprising part would be them attacking in the first place, defence would be easy. Trade and diplomacy the better option if they need something.


How they might protect themselves depends on how far they are from land. Especially from land close by with high cliffs and the like.

500 meters is not at all deep for the ocean. So these balloon cities are either near a landmass or over an ocean mountain.

If the cities are too distant from land for an attack with mechanical devices to reach them, their best solution is to surround themselves with additional balloon trunks on their sides.

Merfolk, fish, and other aquatic creatures can swim under the trunks if they want to go in or out of their walled city. Birds can fly over. While humans could swim under (maybe), they'd be stuck after that. The trunks are too massive to pull even a small boat over (maybe a rowboat with a lot of effort, but no big weapons) and are not simple to swim under either.

If the cities are close enough to land for an attack to reach them, their best bet is to learn how to repair their balloons.

  • And diplomacy.

  • And a slow relocation out of projectile reach.

They can also place additional structures (empty balloons or trunks, or something else) between them and the land. These would serve as decoys and also would block incoming projectiles. If they don't block them entirely, they would slow them down. And allow fewer of them in to have a chance at popping a balloon.

  • $\begingroup$ It kind of seems like you think I mean trunk as in a box. I mean trunk as in the main shoot of a tree. It'd be pretty hard to move around a giant tree, especially in the ocean. $\endgroup$ – SlothsAndMe Feb 6 at 7:26
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    $\begingroup$ No, I think you mean a giant tree trunk. I'm not sure where you get box...how could you float a couple thousand boxes around a city? I mean make an octagon or something out of tree trunks around the city. Secure them to trunks from the ocean floor if possible, and of course to each other. Not easy but not impossible if the residents can direct the growth of the trees (this can take a few years) and also cut them. $\endgroup$ – Cyn says make Monica whole Feb 6 at 8:16
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    $\begingroup$ Good call on surrounding the city with a nautical equivalent of a wall. Additionally, ensuring redundancy of the balloons (i.e. use several plants together, or add artificial floating devices) so that if a few are popped the city doesn't sink can help. $\endgroup$ – G0BLiN Feb 6 at 11:12

In 1000ad the only who could dare go underwater were fishermen.

With no goggles or fins their movement and ability under water will not match the one of meerpeople. It won't take longer for them to realize that it's an unfair fight for them.

Assuming that they are protecting the waters around their ships with some chemicals, and lacking explosive, their only resort is to drop stones from the surface hoping to damage what the meerpeople have built on the bottom.

Keeping in mind the limited capacity of their ships (it's 1000ad, not the Titanic era), they won't be able to carry huge boulders in the open sea. I think you will be able to provide additional protection with reinforced roofing. Keep in mind that, being water denser than air, the stone might reach terminal velocity before hitting, thus lowering the potential damage.

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    $\begingroup$ I think you've misread :D their cites are built on the sides of what are basically the equivilants of underwater seqouias and redwoods. $\endgroup$ – SlothsAndMe Feb 5 at 16:41
  • $\begingroup$ @SlothsAndMe if three houses can have roof, why they can't? $\endgroup$ – L.Dutch - Reinstate Monica Feb 5 at 16:52
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    $\begingroup$ Their homes are more like wasp nests in the sense where there isn't really a defined anything. There's just pockets made of adobe plastered to the trunk that they live in. $\endgroup$ – SlothsAndMe Feb 5 at 17:34

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