The Great City has impregnable walls. No-one has ever overwhelmed them and likely no-one ever will. The only way to defeat the inhabitants of this mighty city is to besiege them and simply starve them out.

The Great City has been under siege for almost a year and stocks of food are running very low. No crops grow within the fortress city walls because the very ground itself is solid rock - carved out from the side of a mountain centuries ago by the ancestors whose magic or technology (no-one knows which) has been lost.

The City has a constant, protected source of pure water within its walls that flows out from under the mountain. The fact that it is filtered through countless layers of rock, means that it cannot be contaminated.

The problem

With a reliable and plentiful supply of fresh water but no access to food or firewood from the surrounding countryside, how can the citizens eat?


They decide that they must capture and eat their enemies. This raises several important questions. I will ask each question separately in a different thread. For now I'll ask exclusively about diet.


Nutritionally speaking, can my citizens, who are normal humans, survive indefinitely on a sole diet of human flesh (by capturing enemies from outside) and pure clean water?

Without firewood or access to any kind of vegetable matter, how can they cook the food or make it sterile enough to eat? Is it possible to sun-dry and then burn their own faeces?

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    $\begingroup$ Define "survive". Is surviving but getting horrible diseases that might kill you years time or shorten your lifespan still ok? $\endgroup$
    – Trioxidane
    Jun 3, 2021 at 20:22
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    $\begingroup$ Relevant xkcd (actually an insightful article) $\endgroup$
    – KeizerHarm
    Jun 3, 2021 at 20:28
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    $\begingroup$ If they can gorge themselves on many enemies, perhaps only eating the best parts, it might solve their problem because there will be no enemies left to lay siege to the city. $\endgroup$
    – Willk
    Jun 3, 2021 at 23:51
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    $\begingroup$ Feces will only be useful for burning as fuel if it contains a significant supply of combustible materials (like partially digested grass from buffalo dung). You might be able to extract burnable oil from the fat of your enemies, but this might involve cooking it and I'm not sure that would be net energy producing. $\endgroup$
    – DWKraus
    Jun 4, 2021 at 3:31
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    $\begingroup$ kinda unrelated, but I am always surprised at that trainwreck of a language that is English... "impregnable" should logically be "impregn-able" = "that can be impregnated". But no, let's mix up identical words with different origins and unrelated meanings! :/ anyways, back to the story $\endgroup$
    – Stefano
    Jun 4, 2021 at 7:24

6 Answers 6


The human body literally contains all the nutrients humans need to survive and thrive. Getting to them is another matter. Some of those nutrients are easy to get by eating flesh, but others will be concentrated in organs, the bones, or blood. Eating bones is flat difficult, and drinking blood exposes you to a lot of potential diseases. Some organs, like the kidney and liver, can contain toxins, and eating them (especially raw) will, sooner or later, result in serious health issues.

Eating raw flesh is mostly safe in the short term, provided it is fresh and the poor guy being eaten isn't already diseased or infested with parasites. Eventually, somebody you eat will be diseased, and in an enclosed area, when one person gets diseased, most of the group is going to get it.

Storing the meat is a serious issue, as raw meat begins to spoil very quickly. Without a way to cook it, it will need to be dehydrated (the sun can do this, or magic). Salting meat is a common means of preserving it, though you will need a lot of salt to do this long-term.

I can't think of any method they could use to preserve the blood, given the constraints you've laid out. It might be possible to dry the blood and then eat whatever doesn't evaporate. I am unaware of any studies about this, how it would protect you from disease (or not), how long the leftovers could be stored before going bad, etc.

In any case, this is going to be very dehumanizing work. Those involved in the processing are going to be severely desensitized and/or traumatized. If anyone they eat has diseases, those are going to crop up in the besieged population. Even if you cook the meat, some of these diseases are going to get out. Without magical support, I don't think it is possible for a community to live on only water and cannibalism for an extended period of time.

If they can at least grow some vegetables and fruit in planter boxes, this scenario becomes much more realistic from a "survival" standpoint. It will still cause severe trauma and change their culture in ways modern humans would find undesirable, to say the least. Some of the population could be sheltered from these effects, but not all.

Sources for trauma resulting from handling bodies:

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    $\begingroup$ Let's not forget Prions (en.wikipedia.org/wiki/Prion). Eww... $\endgroup$
    – PipperChip
    Jun 3, 2021 at 22:02
  • $\begingroup$ Note that black pudding, blood sausages, and sausages in general are things. Black pudding traditionally has pig blood as a major ingredient. Sausages often contain ground organs, too. Bones, I believe, may be able to be ground and included in sausages, or dissolved in vinegar. $\endgroup$
    – rytan451
    Jun 4, 2021 at 6:55
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    $\begingroup$ How would blood/organs work as compost/fertilizer? $\endgroup$ Jun 4, 2021 at 13:59
  • $\begingroup$ Prions are a definite concern. They cause disease though, so are covered in the answer even if they aren't mentioned directly. I tend to be verbose as it is and didn't want to list the specific diseases. $\endgroup$
    – Taejang
    Jun 4, 2021 at 23:16
  • $\begingroup$ I hate to be "that guy", but as for the trauma of processing human meat, can you give us a personal example of how it affected you? $\endgroup$ Jun 4, 2021 at 23:40

You say the plan is to kill/capture and then eat their enemies?

One Question. How? As you have defined the problem the city is under siege. By default that means it has been blockaded/encircled by a superior militarily force which is both preventing the inhabitants both bringing in food and other supplies and preventing citizens from exiting in any significant numbers. (That's how sieges work.)

It also implies that the defenders have no choice but to accept this state of affairs because they don't have the military force needed to break the siege. Otherwise they wouldn't be under siege to begin with!

So if your city is planning to obtain enemy soldiers in big enough numbers to sustain itself they have no choice but to sortie through the city gates and fight pitched battles with the besiegers. And remember besieging armies generally planned and prepared for a siege.

They built fortified camps for their own soldiers well back from the city walls, posted guards all around the city to watch for movement and had things like roving patrols and watch fires. They knew their besieged enemies had the option of sallying forth so they usually planned for that outcome. (At least wise generals did.) They're certainly won't be standing around stark naked covered in garnish and carrying placards saying 'eat me I'm yours".

Now history is full of famous examples of this type of fight but the outcomes are limited to one of the following broad outcomes;

A) The besieged citizens sortie but their attempt is detected and they are driven back inside with both sides suffering losses. However they manage to hold the gates behind them. Outcome - siege continues.

B) As per (A) Above but they can't hold the gates the fighting moves on into the city, usually because the besiegers outnumber the besieged they win. But regardless of the outcome the siege ends. Problem solved.

C) They sortie and catch the besiegers unaware. The besieging army is defeated and retreats. Siege ends, problem solved. (Perhaps they return later but for the moment at least the siege is lifted.)

Point is none of these options are going to deliver enough protein to the city to solve the problem. As long as the attacking general is content to just starve out the defenders without sending troops to assault the walls your city can't access 'fresh meat' without coming out to fight for it. And they will never be able to collect sufficient to feed everyone for long because the only scenario where they are left alone to harvest their prize is the one where they win and the siege is lifted anyway.

One final point - most cultures have a universal prohibition against cannibalism, they will do it in desperate situation (and yes this is a desperate situation) but before they 'stoop' to the level of eating human flesh some of the citizens will consider another entirely plausible option which was also common during sieges.

Betrayal - someone somewhere will consider trading safe access to the city at night to the enemy in exchange for food and protection. It happened repeatedly in historical sieges.

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    $\begingroup$ You're not really respecting the scope of this question. It specifically mentions that there are a lot of problems with the scenario described, and that this specific question is only about the nutritional value of humans. $\endgroup$
    – KeizerHarm
    Jun 4, 2021 at 5:19
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    $\begingroup$ Actually I believe I am. Yes the author asked whether it was feasible for the citizens of his/her besieged city to survive of human flesh i.e would it be nutritious enough to sustain the population. But ... they also expressly stated that the intention to eat enemy soldiers and only the enemy soldiers. Which immediately raises the problem I mentioned i.e. how do you propose to get enough of them to feed everyone? $\endgroup$
    – Mon
    Jun 4, 2021 at 6:38
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    $\begingroup$ Getting enough humans to eat is a different question from the nutritional value of humans. $\endgroup$
    – KeizerHarm
    Jun 4, 2021 at 7:03
  • $\begingroup$ @KeizerHarm. I don't think that the question is solely on the nutritional value of human, if it were then there then it probably wouldn't mention the siege at all in the first place. $\endgroup$
    – Dast
    Jun 4, 2021 at 9:35
  • $\begingroup$ I agree with the criticism. The difficulty of capturing enough enemies will be another part of my question. Perhaps you could answer when I ask that part. ;-) $\endgroup$ Jun 4, 2021 at 10:51

Human flesh is remarkably nutritious and you could likely survive on a diet of humans for quite a long period. That being said, there are reasons why no species or culture has ever evolved that relies primarily on cannibalism, mainly that it's not exactly easy to make a living hunting prey that has senses and intelligence equal to yours. Investing that much effort into every single hunt would very rapidly doom your culture. This is less of a problem in a wartime situation, since people are dropping dead all the time, but if you want your city to survive entirely on cannibalism, you have to take into account how good humans are at avoiding getting eaten.

Diseases, especially prion diseases, would also be a huge problem, just as they were in real-world cultures that practiced cannibalism. Kuru, for instance, is a neurodegenerative prion disease that was once prevalent on the island of Papua, where it was spread almost entirely through ritual cannibalism among the indigenous population. It's incurable even with modern technology and has an extremely long incubation period (in some cases as long as 50 years), making it basically undetectable as well. In general, eating your own species is risky, since anything that made your prey sick can also make you sick.

All in all, it's doable in the short-term, but your city is massively screwed if it has to rely exclusively on cannibalism for a longer period of time. It might be safer to just turn your foes' bones into fertilizer to grow better crops (bone is actually pretty good for this).

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    $\begingroup$ Someone had to mention prions. $\endgroup$
    – DWKraus
    Jun 4, 2021 at 3:24

It has happened in the past, like in the case of the whaler Essex

Essex was an American whaler from Nantucket, Massachusetts, which was launched in 1799. In 1820, while at sea in the southern Pacific Ocean under the command of Captain George Pollard Jr., she was attacked and sunk by a sperm whale. Thousands of miles from the coast of South America with little food and water, the 20-man crew was forced to make for land in the ship's surviving whaleboats.

The men suffered severe dehydration, starvation, and exposure on the open ocean, and the survivors eventually resorted to eating the bodies of the crewmen who had died. When that proved insufficient, members of the crew drew lots to determine whom they would sacrifice so that the others could live. A total of seven crew members were cannibalized before the last of the eight survivors were rescued, more than three months after the sinking of the Essex.


  • some of them managed to survive on that forced diet. And they didn't have a supply of fresh water

  • they didn't worry too much about cooking their meal, because for obvious reason when on a shipwreck in the middle of the ocean wood is not exactly the most abundant resource.

  • $\begingroup$ There's also Uruguayan Flight 571. They only ate the dead, of which there were a fair number. Rescue came 72 days after the crash when two of them managed to hike out. $\endgroup$ Jun 7, 2021 at 2:58

Probably Not

The human body, naturally, contains all the basic nutrients a human needs to survive. So as long as you're careful to eat all of it (grind up the bone to put in sausages, drink/use the blood in cooking, eat most of the organs) you'll get everything you need from cannibalism to survive. It might not be the perfect diet, I'm not an expert in all the vitamins and minerals a human needs to know if there's Some Specific Thing which you'll be somewhat deficient in if you only eat people which might lead to long-term complications. But the diet will be at least as "healthy" as a normal medieval diet.

That being said, how many corpses would you need? James Cole estimates an adult human body contains on average 125,822 calories. Source Caloric consumption for an adult human is roughly 2,000 calories a day. (Cole believes that a modern human's average need is 2,4000 calories a day. Not sure why, so I'm sticking with 2,000 as the more widely-accepted figure.) That implies a single human body could feed 62.9 people for a day. Of course there's going to be "wastage" in the corpse as you're unlikely to eat 100% of it. Assuming 15% wastage (loss of caloric value from spilled blood/missing bits from hacking your victim to death outside the walls, etc) means your average corpse feeds 53 people a day. Call it 50 in round numbers. So for every 50 defenders in your castle, you need to kill one attacker every day AND recover the corpse. Of course, you might not get "just" humans in your attack. I couldn't find a full-body caloric assessment, but just the muscle mass of a horse yields 359,100 calories. Assuming that's the maximum value you can get (medieval horses were smaller, there's some wastage which may or may not offset whatever added caloric value the blood and bones get you) a horse can feed about 179 people a day. But as cavalry aren't really "storm the walls" troops, you can't rely on the enemy keeping horses anywhere near enough for you to snag. So the question becomes, can the defenders achieve a kill ratio of 1 attacker per day for every 50 defenders?

I believe the answer is a firm "No." Assuming the enemy has 2x the amount of men as the defenders (Since 2x would preclude the defenders just sallying out en-mass but is less than the 3x generally thought sufficient to storm a fortified position with a chance of success) That would involve inflicting More than 1% casualties on the enemy every day for as long as you need to live purely off human flesh. Sieges were long, drawn out affairs. The enemy likely will keep out of bowshot most of the time, relying on starvation to take its toll. This means any sally for "provisions" will require a force from the castle going at least 100 yards (and likely longer, depending on your bow tech) from the castle, into the enemy camp, killing some of them, and then dragging the bodies back. The dragging back is the killer here. I can see a vicious and aggressive besieging force launching tons of attacks, and POSSIBLY inflicting a kill per 50 every day. But you have to get the body back, as intact as possible. At some point your enemy will realize you're literally eating him and do everything in his power to stop you.

Unless you're some sort of horror cult that cannibalizes in peacetime, they'll know you're low on food. The attacker will simply pull back even further, fortify the siege lines even more heavily, and fight like hell to protect their dead from desecration. Which means you won't recover every corpse. Which means you need to kill even MORE of the enemy. As a 1% daily attrition rate would end the siege in a max of 80 days (the point where your besieged force significantly outnumbered the attackers that started 2x the size) Killing even MORE of them makes the whole concept of your defenders being besieged to the point they need to eat the enemy dead redundant.

You can offset this somewhat by the defenders eating their own dead as well, but that leads to diminishing returns. A starving person is a lot fewer calories than a healthy one, and likely deficient in key nutrients that would cascade as anyone eating them wouldn't get those nutrients from the corpse. Though I admit I'm not sure how long one could live eating your own dead while "augmenting" any missing nutrients from enemy corpses, the end result still seems like you'd need to many deaths to keep the siege viable, one way or the other.

  • $\begingroup$ I had a short sidenote on the problem of disease, but the site told me my answer was spam until I took it out. Not sure why, but sparknotes is "eating people, especially uncooked people, is dangerous for your health. But as sieges are always a hotbed of disease I see this as a short-term problem that can be overlooked for the purposes of plot in the same way not all siege stories have a cholera or other disease outbreak. $\endgroup$ Jun 4, 2021 at 12:52
  • $\begingroup$ Vitamin C is not contained in most meat, but one organ meat, spleen, does have a fair amount. Two 3.5oz servings per day would meet nutritional needs. $\endgroup$ Jun 4, 2021 at 21:22

In addition what other people already gave as answers: I saw a documentary that stated that the human body contains many nutrients needed for survival, thus cannibalism is a valid option. However, this is only true in case the human that is being eaten is not starving themselves, in that case, the body does not contain enough for a human to survive on and it will only give the false sense of eating enough, purely based on mass and a 'full' stomach.


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