It's a sprawling city, similar to that of Whiterun (capital of Whiterun Hold in Skyrim) with about 1500 inhabitants. Assume medieval-level technology and weapons, and also assume that the city is fairly sloped with a few natural hills scattered here and there.

The land there is still fertile, so about 400 farmers work the fields to provide food for the rest of the city, while there are about 200 merchants and traders who have small shops scattered around the city. Below the hills lie a valuable resource underground: precious ores and minerals. To exploit their natural resources, there are 100 miners in the city. The city is governed by a king, so there about 100 people who serve the king (servants and his cabinet). Another 300 residents are part of the city's army, tasked with defending the walls from foreign enemies, as the city is in the midst of a war with a neighboring settlement (with around the same population) that is located about 250 miles away. The remaining 400 are children.

Now to the question: Why would the people of this city always sleep during daylight hours (~7 AM to ~7 PM), while getting up and working during the nighttime (~7 PM to ~7 AM)? Anything I haven't stated explicitly stated in the question can be implied however you would like to support your answer.

I've only thought of two possible reasons: 1) their primary source of profit and sustenance is agriculture, and they mostly grow plants that grow more at night (like pumpkins), so eventually their culture evolved around this agriculture or 2) the temperature in the day is unbearably hot, so they need to work at night when cooler winds pass through.

Note: When I say the whole city sleeps during the daytime, I don't literally mean everyone, rather, I mean the vast majority of the residents. Those who aren't sleep will be inside of their own homes. Also, I'll be accepting an answer based on how many possible reasons the answer offers for this peculiar behavior. After all, this will be more convincing in my novel if there are several reasons, rather than just one, for this behavior to occur in the city.

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    $\begingroup$ This sounds a little bit like Idea Generation, but I'm not positive. $\endgroup$ – HDE 226868 Mar 16 '16 at 23:37
  • $\begingroup$ 1500 seems awfully small for a city, even then. I'd double or triple it if you want the sense of a "sprawling city." See en.wikipedia.org/wiki/… (and that's England, which was small). $\endgroup$ – CAgrippa Mar 17 '16 at 1:48
  • $\begingroup$ It seems like a small number of children for a setting with medieval technology, you might want to consider increasing the amount. $\endgroup$ – Xandar The Zenon Mar 17 '16 at 4:20
  • $\begingroup$ Heat. Consider Las Vegas, or the southern European custom of the siesta, taken to an extreme. $\endgroup$ – jamesqf Mar 17 '16 at 4:44
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    $\begingroup$ Why the downvote? $\endgroup$ – fi12 Mar 17 '16 at 15:49

12 Answers 12


A Dragon

There is some monster that will hunt people. This monster only hunts during the day, so people stay hidden.


The sun burns people much worse in your city than it does elsewhere. Maybe they have some kind of ozone hole above them. People who make a habit of going out in daylight will get sick and die.


An important food source or export of your city is a plant/insect/mineral that is hard to find in daylight but glows at night.


In your city, heavy rain and snow are very common during daytime, very uncommon during the night. Or days are very hot.


Your city grew around a signal tower or lighthouse, where the original inhabitants had to work at night and later additions just kept to that rhythm.


Plants tend to produce pollen during the day. A plant around your city has toxic pollen and people sleep all day to avoid it.

  • $\begingroup$ Interesting that this ended up being the accepted answer. Perhaps the question was framed differently, and perhaps the OP simply didn't feel the need to apply all the question's current stipulations. It's a good answer, but all but History are unlikely to qualify under the clause of, "Why would the people of this city always sleep during daylight hours..." unless you're dealing strictly with rational agents, not something humans are known to be. But hey, if it's good enough for NPCs... lol $\endgroup$ – kayleeFrye_onDeck Oct 4 '18 at 23:55

There are several reasons why this would happen.


Daylight means more visibility. Perhaps some visual hunter/enemy (griffins, humans,etc...) is present and the people want to avoid conflict. As you said the heat/the sun is dangerous. Perhaps as JD suggested this is because of a genetic mutation. Possibly some of the ores are radioactive.


Food sources quite often sleep at night. This would make night hunting easier. Nights are good for stealth.


Their religion may require avoidance of sunlight/heat. Or only slaying animals at night. Maybe a lunar religion?


Due to a founder effect and/or genetic drift of an isolated population, people are largely "night owls" who simply prefer it that way. Or they can't tolerate bright light (for same reason).

There are (or were) preditors that were dinural, so people had to stay locked in their homes until night.

It's a high altitude with strong UV radiation, and the founding population was sensitive to having their eyesight damaged and any exposed skin burned.


Sensitivity to light

A curious genetic variation in the ancestors of the founders corrected that most salient evidence against the Argument From Design: that the human retina is mounted backwards. These people instead have the retina mounted the "right" way, with the receptors aimed towards incoming light.

While this gives them excellent night-vision, it also means they are very sensitive to bright light. It simply hurts the eyes too much to be out in daylight.


8 answers so far and nobody mentioned the simplest one...

The locals are vampires !

That also nicely explains the war: The neighbors want to exterminate them for obvious reasons.

  • $\begingroup$ Lol! Of course. $\endgroup$ – Aarthew III Mar 20 '16 at 19:24

There are several reasons why the bulk of the people are only awake at night that haven't been touched on yet.

Camouflage - They don't want anyone to know they're there - The city is too far away for others to harvest the crops, and the city specifically looks abandoned so people will leave them alone. Alternatively, the buildings may themselves be blending in with the environment

Food - Nonstandard crops which have specific cycles that grow or bloom at nights. Nonstandard herd animals that happen to be nocutrnal. There could also be a particularly vicious/deadly type of insects in the area (think bees/wasps) that operate during the day, so harvesting and planting at night is a means to that end.

Extenal Forces - You spoke of markets, merchants and tradesmen - perhaps they are nocturnal because another neighboring area is also nocturnal, so they trade with each other in the darkness.

Perhaps the area is very expansive in addition to being very tropical, with both high direct heat and punishing humidity. Moving at night limits allows quicker travel that's easier on not only the people, but work animals (horses, mules, et cetera) as well.

Darksight - Mining is an important part of religion & society, so having good darksight is incredibly important. People who need the sun to see could be considered weak. They may also worship the moon as an extention of it.

Glowing - Perhaps this society has some basic or tribal understanding of radiation or magic, so they are constantly on the look for glowing rocks. This could be something they collect to craft (think of the old radium watches) or magic (think Ioun Stones) or worship, or something they're scared of and avoid.

War - You've mentioned they're in a war-like state with a neighboring area. If they operate in a guerrilla manner, that would work best with a nocturnal defense force. Perhaps the neighboring country also has nocturnal forces, either out of tradition, one of the above reasons, or they fight that manner out of honor, similar to the Ol' West's fascination with "High Noon".

  • $\begingroup$ Just fyi pretty much everyone mentioned heat. Other than that nice answer. $\endgroup$ – Aarthew III Mar 18 '16 at 4:06

Heat. A clime that is searing during the day but cool at night year-round (such as some desert climates) would predispose anyone adapted to it to being a night owl. (This would mean either irrigation or the use of succulent crops such as prickly pear cacti, but that can be worked with.)


There is something in the water :

There is some chemical substances in the main water source of the city that has the effect of making everyone who drinks enough water to sleep during the day rather than the night, the minority who doesn't sleep during the day are the ones who drink much less water, maybe because they live far away from the city's main water source, or maybe they suffer from dehydration.

  • $\begingroup$ Why would water effect your sleeping pattern? $\endgroup$ – Aarthew III Mar 17 '16 at 15:05
  • $\begingroup$ @AarthewIII I am imagining the existence of a certain chemical compound in the main water source of this city which is responsible for this massive sleeping disorder. $\endgroup$ – Javert Mar 17 '16 at 15:23
  • $\begingroup$ interesting. Do you know of any chemicals that do this? That's a pretty cool idea. $\endgroup$ – Aarthew III Mar 17 '16 at 15:26
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    $\begingroup$ @AarthewIII It's known that Magnesium can help you fall to sleep faster and deeper, maybe the main water source of the city when exposed to sunlight causes a chemical reaction that makes the water saturated with Magnesium and that's why they sleep during the day. It's just a theory. $\endgroup$ – Javert Mar 17 '16 at 15:40

Perhaps these people were originally from a region far from the equator, and therefore have extremely light skin in order to absorb UVB radiation and make vitamin D. Then if they were displaced (war, natural disaster, etc.) and forced to move somewhere near the equator with a lot of direct sunlight, without the invention of sunscreen or enough resources to make like, giant hats or something, they'd need to work at night to avoid sunburn and skin cancer.


There is a real genetic condition that make people extremelly sensitive to the sun, to the point that they can only go outside when it's dark. Xeroderma pigmentosum: Individuals with the disease have been referred to as "children of the night". https://en.wikipedia.org/wiki/Xeroderma_pigmentosum

There is a small city in Brazil where 24 people have this disease, making it the place with the highest density of the condition. http://g1.globo.com/goias/noticia/2014/05/povoado-em-goias-tem-maior-taxa-mundial-de-doenca-rara-de-pele.html (in Portuguese)


Disease. There is a day-only insect that carries some nasty disease. The insect will not enter a dark space and will shut down and sleep if it becomes dark. Thus during the day everyone stays indoors and puts opaque coverings across any opening. Artificial light (ie, candles) can't be used because a bug that accidentally was in the room (it was on something that was brought in) would wake and become a danger.

Since they can do nothing during the day they sleep. Working by moonlight isn't good but it's better than the alternative.


Alright. The original answer was too long so here's the abridged one:

So we're working with,

  1. Microscopic adversaries
  2. Airborne mobility
  3. Day-cycle propagation
  4. Inimical to macroscopic organisms due to their inability to concentrate enough neutralizing agent

The details:

  1. Method of mobility: I chose consistent fog-banks or the local humidified air itself getting "doped" with organisms that could move around in it and kill humans and presumably other animals that are fighting for space and breeding potential and therefore unlikely to stay on the water when active

  2. Method of delivery: I chose envenomed quills-as-seeds being distributed constantly to fit a nice middle-ground between inability to destroy infrastructure entirely while still pretty dang corrosive, making things like wood insufficiently robust. The OP's land is not exactly rolling in enough gold to turn the entire hillside(s) into a covered stone fortress after all. While this delivery mechanism might seem like something unlikely in nature, consider something perhaps like bacteria that lives by necessity on or near water, just not inside of it due to insufficient robustness in the presence of water-pressure. Now imagine this bacteria is constantly breeding and requires either photosynthesis or radiation for sustenance, and goes dormant in the evening. Now go one step further and justify the constant barrage of quills; easy, they act more like seeds that compete with other organisms in ostensibly lethally manners while in contrast to their own kind is their very method of reproduction! This is hardly unprecedented in nature; the male bed-bug for example tears open the body of its mate instead of using an evolved orifice. If you're not too squeamish, you can look to see what Wikipedia says about traumatic insemination. Presumably these quills would be too prolific during the day, and the inability to even see this agent of death would make it an intractable problem for the humans due to their current level of technology.

  3. Method of exclusion: so how exactly is it killing humans but not plants? This might actually be a trivial problem of chemistry. It's quite possible that high enough concentrations of specific minerals or chemicals can act as a neutralizing agent, which might aid plants or bacteria that gobble up the local environment due to shear concentration; that would be unlikely to concentrate in high enough levels across the entire body of the human, especially if it's specifically a chemical broken down by the liver. Now taken one step further if you like and this can be used as an infrastructural limitation to keep the kingdom and its people limited in their rate of expansion, meaning that only wood from trees from that region or regions with similar available nutrients can withstand the harsh environment after a lifetime of being concentrated with the neutralizing agent.

Now we're left with all the core ingredients to keep those poor humans locked up during the day, presumably perpetually as they can't even see what's killing them when they go outside during the day regardless of the time of year.

Not only is this now a well-defined potential root-cause, it has plenty of plot-potential all on its own for working with or around the unseen hazard as well as efforts to understand it due in part to such a low level of technology to work with, even with Magic being available. I'll spare you my musings on those possibilities for numerous reasons.

I'm dubbing this,

The Unseen Swarm

but the locals in that world would likely dub it something more akin to,

Day Plague


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