Similar question to this one except I want to calculate the urban and rural population needed to support an army.

I want to create a world for a fantasy wargame campaign using some of the elements from questions I have asked here before. The setting is a desert world where water is relatively scarce, but is otherwise similar to earth. There is a large canal network to move the water where it’s needed across many hundreds of miles and the world is populated by humans.

There is a technology level similar to that of ancient Rome 100CE and a civilization based on city states located at the junctions in the canal network. Each city has a fairly large area of influence into surrounding territory. Some are larger some smaller.

In order to construct a vaguely realistic campaign in this world I need to consider the population size and spread.

Is there a basic rule of thumb that I can use to determine population sizes in rural areas, towns and cities? There needs to be enough people so that each city territory can field an army of between 5000 and 20000 without too much trouble.

So in summary what I want to know is for an x thousand man standing army how many people have to live in the city and how many in the rural areas along the canals? Use Roman settlement patterns if I have left anything out.

Out of scope: anything to do with how the canals were built or the backstory (and no magic).

Edit To answer some questions that have been raised:

Do they have slavery yes they do as the Romans did.

Fighting usually occurs in the spring and summer, although there might be exceptions. Some city states have taken control of others to form small nation states. There is considerable tension along many of the canals in contested areas. I’m not sure how wide the canal irrigation zones are but probably 10-20 miles either side of the canals are agricultural land the rest is desert.

There is one harvest per year at a similar time to that which the Romans would have experienced and it is labour intensive.

Conscription would not be used except in emergencies. In such cases any males from the population who might be reasonably fit and capable in a fight (say 15-55 year olds) might be called up for the duration of the emergency.

Map added of the top half of this fictional world in case anyoen is interested Map sample]

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    $\begingroup$ What is the warfare convention? Is it a summertime activity like ancient Greek city-states (fighting to move the border between)? Or is it year-round (real conquest of a neighbor)? Is there conscription? If so, how many years? How many harvests per year are there? And how do those match the good fighting weather? $\endgroup$ – user535733 Nov 11 '17 at 14:10
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    $\begingroup$ Agree with previous. Since you are specifically talking about city states using classical republics as a model seems natural. That would mean that all citizens would be available. Generally that would be adult males who are not slaves or foreigners? So do they have slavery? Other disenfranchised sections of population? Are women considered citizens? $\endgroup$ – Ville Niemi Nov 11 '17 at 15:09
  • $\begingroup$ @user535733 I have edited the question to provide further details $\endgroup$ – Slarty Nov 11 '17 at 16:33
  • $\begingroup$ @VilleNiemi I have edited the question to provide further details $\endgroup$ – Slarty Nov 11 '17 at 16:33
  • $\begingroup$ You need to think about how your setup developed, and specifically where and how agriculture spread, before you can support cities at random places in the desert and dig canals to them. Where does the water in the canals come from, and why do you think populations won't concentrate around the water sources instead of your desert cities? $\endgroup$ – Spencer Nov 11 '17 at 17:23

Copy something real.

  • Pick a city of the ancient world of roughly the time period you want. There are many which could be candidates. Cairo. Alexandria. Samarkand.
  • Duplicate that city in your fiction. Most readers will not be familiar enough with the ancient world to identify what you have lifted. If you are an excellent writer an occasional one might (especially if you decide to include the Hagia Sofia in your city); that is fine and part of the fun.

Kandahar would be a fine choice.


Kandahar was founded by Alexander the Great and by the time period you state was a regional capitol. It is hard for me to find population estimates for the ancient city, but comparable cities had populations in the low hundreds of thousands and certainly the surrounding countryside would have many more.

As regards how to estimate populations I found this. estimating populations for ancient egypt from The Complete Cities of Ancient Egypt, Stephen Snape. They discuss various ways to estimate population for ancient periods, either based on likely productivity of the land or extrapolating from urban populations to what would be needed to support them with food. You are probably not going to find a place with better archaeological / historical records than Egypt. Maybe Greece or Italy. Note that urban population is not one city but all urban centers of the time.

I cannot recall reading a work of fiction that got so far into the weeds as to discuss population density and irrigation practices. I suspect people who are thrilled by such are not reading fiction.

I figured Alexandria and Cairo must have had canals. In fact all of these ancient drylands cities had canals. You can see one in the above photo of Kandahar. It turns out that the ancient underground canals of Alexandria were once a tourist attraction, and might be again.


This is fortunate because these subterranean canals were frequently described as underground cathedrals. Sometime between 1710 and 1712, Francois Paumier, a member of the third order of St. Francis, exclaimed with admiration, "there is nothing more beautiful and complete than the vaults; nothing better constructed than their apertures; nothing more superb than the pieces of marble with which they are surrounded". Seventeenth and eighteenth century artists, including the scholars of Napoleon, though enough of these monuments to make numerous engravings, which give us an idea of their imposing proportions.

roman cisterns of alexandria

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    $\begingroup$ As regards getting into the "weeds" of population density and irrigation, I think you are right, but I would add that this is the setting for a war game campaign on a desert world so irrigation and population may be of more interest than they would be otherwise in works of fiction. I just want to get the numbers roughly right :o) $\endgroup$ – Slarty Nov 11 '17 at 21:16

There is a very rough rule of thumb that ancient farming methods could support one non-agricultural worker for every ten agricultural workers. Families are included in these numbers, because they will do useful stuff -- watching the herds, spinning wool, cooking for the peasants, watching the manor, spinning wool, teaching the children for the upper classes.

  • That means one farm worker produces food for 1.1 people. If agriculture is a few percent more or less efficient, the ratio of non-farmers to farmers will change by a much greater percentage!
  • Except for very short campaigns, there is a limit on the number of soldiers who can be mobilized. If more than 9% of the men are called up, there are not enough left to work the land and feed everybody.
  • More likely, perhaps one in ten non-farmworkers can become a soldier. That would give a ratio of 100 agricultural workers to one soldier. Of course a society could compensate by mobilizing women, children, and elders even more than the 10-1 ratio assumes, but I'm already assuming that they contribute anyway.

So 10,000 soldiers might be part of 100,000 non-agricultural workers. Say half of them live in cities, half in smaller towns and manors or villages (assume an even split). They are fed by 1,000,000 farmers in manors and villages. Since that is just counting the able-bodied men, triple or quadruple the numbers to get the total populations.

  • 4,000,000 farmers and their families in villages
  • 90,000 non-farmers and their families in villages
  • 90,000 non-farmers and their families in towns
  • 180,000 non-farmers and their families in cities
  • 30,000 military dependents (Decide where they live. Manors? Cities?)
  • 10,000 military

4,400,000 people total

Follow-Up: I assumed that one quarter of the population would be men of somewhat military age. The assumption is that half of the population will be women and that half of the men will be too young or too old to fight.

And "one in ten" or "ten percent" are very rough guesstimates. Make it "one in eight" or "one in twelve" and the army size changes accordingly.

Just like the division of populations between cities, towns, and villages/manors, this would be one area where some of those fictional countries get their distinct look-and-feel.

  • One country might have laws and economic patters which favor manors with absentee landlords, operated by slaves and overseers. Few little towns, and most freemen are in the cities where skilled craftsmen compete with factory slaves.
  • Another country might have laws and traditions that keep craftsmen at the village and town level, serving the needs of yeomen farmers. The cities are little more than rural towns with an attached palace and a few bureaucrats, plus the service sector to keep them fed in style.
  • One country might be oppressing the peasants, so they don't draft them as a militia, and they don't dare to call up too many of the combat-trained gentry away from their manors, either.
  • Another country has the tradition to train all young men to fight, and they call them up by age group -- first the current draft, if they need more then last year's reserve, and so on. On paper they can field enormous armies, but if they do that they cripple the ability to arm and feed them.
  • Another country uses their standing army as a labor pool for civil engineering projects in between battles. (Or has them grow food to feed themselves, for that matter.) That allows them to increase the size of the army relative to other sectors of the workforce.
  • Yet another country trains both men and women of their "fighting classes" to fight (whatever those "fighting classes" are, see above). They deploy all the men to fight in their expeditionary forces, and still have a substantial garrison at home.
  • $\begingroup$ Excellent! Although I’m unsure about your quadrupling step. From the refs below it the Roman Empire may have had a population of very roughly 45 million in 100CE (based on estimates given from 14CE and 350CE) and that in 100CE the army included roughly 400,000 soldiers all in. So almost 1 in 100 which is close to your initial estimate before the quadrupling. Also do you have any reference to the urban/rural split or was than a personal estimate? en.wikipedia.org/wiki/… en.wikipedia.org/wiki/Demography_of_the_Roman_Empire $\endgroup$ – Slarty Nov 11 '17 at 18:27
  • $\begingroup$ @Slarty, see my follow-up. $\endgroup$ – o.m. Nov 12 '17 at 11:17

Ballpark numbers:

  • Grain farming takes about 1 acre per person, more in drier climates. You also need land for other uses for the peasants -- wood for heating, pasture for livestock. You would be reasonable to use 200 people per square mile. Rice permits somewhat lower land requirements. Irrigated land can double the productivity, as can the right climate. Drought can reduce the crops to 1/5 of normal.

  • Stirling in his Emberverse books cites 3% It takes around 30 peasants to provide the resources for a man at arms. This fits with other numbers I've seen.

Another answer here cites 10 peasants per non-peasant. Given that any culture that creates more than mobs armed with clubs requires other non-peasant/non warrior personnel,(E.g. the local village has a miller, a black smith, an inn keeper, all with their assorted minions, the manor house with servants...) I'm inclined to go with 3%.

  • The working class as fighters didn't happen much until firearms. It takes a long time to become competent with sword, pike, sling or bow. (I'm sure someone will find exceptions to this... Warrior cultures such as the Mongols and the Spartans) Professional soldiers coming up against peasantry does not end well for the peasants unless present in overwhelming numbers. Mind you, the Romans ran into some nasty surprises in what is now Germany -- special circumstances. These exceptions make for interesting sub-scenarios in a military game.

That said: A pruning hook isn't much different from a halberd. A scythe blade can be remounted as a pike blade.

  • If you get the peasants involved, you need to do this after planting and before harvest. One the reasons the Irish have a rep for fighting: Potatoes are an easy crop that takes little care.

  • If you look at the French Indian wars in North America (7 years war in Europe) you find long marches by absurdly small forces making significant changes in the strategic situation. Francis Parkman has a series of books on these wars. They have to be read with consideration of his British/settler vs French/Indian savage bias, but for some idea of the personalities and logistics they have much merit.


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