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Lots of fantasy books have medieval style warfare in them and armies march all over the place to face one another in battle. Sometimes these armies are tens of thousands large, or even hundreds of thousands.

These soldiers in the real world would need to eat, sleep, have shelter and battle equipment. On the move many of these things will be damaged. A soldier with a broken sandal is going to be a hindrance to his companions.

So they need to be equipped and fed. So taking a medieval level of technology, how large could an army be and still move as a 'unit', be supplied and be able to fight at the end of say 500 mile march? I assume there will be a bit of hunting and scavenging. How much of an average soldiers nutrition was supplied by the army and how much was left up to them?

For some reason I'm thinking that Napoleon was the first to have armies in the 50,000+ range, and is also quoted as "an army marches on it's stomach". It was logistics that was his primary failure when he went after the Russians (thanks to generals Mud and Snow)

What is a reasonable sized army to expect to be mobilized? It appears Hannibal had over 50,000, I also expect they did a lot of raiding.

Let me know if this question needs more refining.

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  • $\begingroup$ Is this question European specifically? Because Napoleon was not even close to the first.. $\endgroup$ – FiringSquadWitness Sep 16 '15 at 3:29
  • $\begingroup$ au.af.mil/au/awc/awcgate/gabrmetz/gabr0009.htm $\endgroup$ – krowe Sep 16 '15 at 3:37
  • $\begingroup$ @krowe Do not answer in comments, answer using the text box below. $\endgroup$ – PipperChip Sep 16 '15 at 4:04
  • $\begingroup$ @PipperChip Just providing some more accurate information for anyone thinking about to answering. This is not an answer to the question asked at all. $\endgroup$ – krowe Sep 16 '15 at 4:30
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    $\begingroup$ @krowe if only there was a historical basis to that.... $\endgroup$ – FiringSquadWitness Sep 16 '15 at 4:47
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Rather than list off examples from history I am going to give you a rundown of things to consider when gauging size.

  1. This should be obvious but, how big is the other army? Over-sized armies can actually end up defeating themselves so to speak if they get too big, they become disorganized and starve to death. Your opponent helps define your army (or it should at least), base your force size/structure/make-up on what you are being confronted with.

  2. How far is this army going to have to go from its base of operations. Home-(battle) field advantage is a thing for a reason, the closer you are to home the easier it is to keep an army fed, meaning more troops are available.

  3. What kind of climate and geography are we talking about? Lush plains full of food or barren rocky crappy desert? Feeding and watering a large army is tough...and on a side note remind the troops to poop down river from the cooks...

  4. Population base. You still need people to run your cites and day to day operations (unless you are working with a pre/early conquest Mongolian horde I suppose) and to serve as troops. The number that is most often floated around here is around 8 to 1 though as the army grows and its needs expand things seem to slide more towards 10 or 12 to 1. (Civilian to military)

Been working on a formula in my head, there are surely more modifiers but it would look something like this.

enter image description here

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  • $\begingroup$ This is closer to what I was looking for, more of a formula, but having some examples and how they worked is good too. +1! $\endgroup$ – bowlturner Sep 16 '15 at 14:15
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Napoleons armeis, and the revolutionary armies that came before him were supported by a vast network of private civilian contractors who supplied the armies. Supplying the armies was a huge (private) industry during this time and it made many such contractors fabulously wealthy. Even then, they still relied on living off the land to a large extent.

Moving back a bit in time we have the Thirty Years War in which hundreds of thousands of mobilised troops, mainly mercenaries, lived off the land in Germany for decades, to some extent supported by logistics networks (of which the most famous was Wallensteins huge war machine) , but more than often left to their own devices. Of course this did cause the utter ruination of Germany.

So really all these armies and certainly those that came before them lived off the land when in the field, and when these armies were standing armies they lived off the land when quartered at home also (even if they were quartered in Roman forts or whatnot). What tended to limit army sizes prior to 1500 is the economic constraints arising from feudal systems and the limited number of trained troops that existed (bowmen, pikemen and cavalry needed a lot of training).

The later armies got much bigger not so much because they changed the way they fed themselves, but firstly because musketeers were easier to train than bowmen or pikemen, and secondly because political and economic changes in nations allowed for widespread conscription.

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The real restriction on the range of an army is the horses. Imagine your army heading out into a place with no food. Every day you march, you need to put food in the wagon to feed the horses pulling it for 2 days. At a point, you have to fill the entire wagon with food for the horses pulling said wagon and you are stuck. This distance is pretty short, and that's just to feed the cart horses and not the army.

Foraging can help some, but it also restricts the distance you march, and a large army will exhaust an area rapidly. Think of how fast your pantry would empty if you had 50 guests for dinner every day.

So in reality, nations needed to keep a supply of depots to store food, and river transport to help fill them, and many other logistic support systems to allow an army to go anywhere. Any interruption of this system would bring an army to a halt, even with no opposition. Bad weather often did this.

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Note 1 : I will use SI units for my calculation

Note 2 : I assume that water will not be a problem and that your army will always found a river or lake. Also I assume that your army will be disbanded after reaching the objective, not taking in account the need for them to go back afterwards.

First of all, the humanitarian daily ration weights 850 g. Since it is optimised with modern technologies, I think that a 1 kg daily ration is a reasonable estimation of the weight of a medieval ration.

If each soldier carry its own supply, your are only limited by the weight they can carry in addition to their usual equipment. If soldiers can carry 10 kg of supply without being crippled, it means 10 days of autonomy. Of course you have to gather the starting supply first, but with that logic you can gather it as the same time you gather your army, since your men carry their supply. It means that at peace time you should keep your (potential) army dispersed through the land.

Then, you want to march 500 miles (800 km). By assuming that your army walks 8 hours a day at a speed of 5 km/h (only possible if you have good roads), it will take you 20 days to reach your destination (not that this is the best you can do, the real number will probably be much smaller, for example if your roads are not that good or if you are in unknown territory).

Therefore with the most optimistic estimation, you can only travel half the plan distance with the "self carrying supply" method.

Note : if your army fully rely on horses, as the Mongolian one, you are both faster and able to carry more stuff. But I focus here on marching army.

If you want to carry the supply, it becomes a nightmare very rapidly. For the 10 days remaining and a 10 000 men army, you have to gather and carry 100 metric tons of food (without taking in account the additional men and animals needed to carry it). It does not look very practical.

You can not really send the supply to your army, since it would need to travel faster than your army. If you have a faster way to travel, your army should probably us it. But if your army need to stay somewhere, it is a good idea.

In the other hand, you could use "walking supply" such as living cow. Since a cow can be estimated to weight around 500 kg (the estimation given in the link is higher, but medieval cow were probably lighter), only 200 cows are needed for 10'000 men and a 10 days march, this seems reasonable. They can even carry stuff with them and you can milk them. Well you still need to feed them, and they can be quite slow (I doubt they will walk 8 hours a day), thus expanding the time you need to reach your destination.

All this together makes that you can probably not go further than 50 000 men with this strategy (already at least 1 000 cows are needed).

Note : if you are a Mongol you can simply milk and eat your horses

You can still eat what you find on your way. Hunting does not seem efficient, since most of your time will be dedicated to walk toward your objective.

However using the supply gathered in the towns and village you pass by is quick and give you plenty of food (you have an army, you can seize what you need if the people do not want to give it to you). If there is a 30 days reserve of food, it means that each inhabitant of the land you go through can "provide" supply for 30 soldiers (and afterwards starve to death).

I think this is the really limiting factor. By travelling through a very populated area, you can handle a very big army. Going to a 10 000 inhabitants town each day let you feed 300 000 soldiers (with our assumptions). Actually this was the main strategy used during medieval times, and it explains why war did cause such terrible famines and destruction : armies just scavenged what they needed.

Note : if you reign over a big empire, storing food everywhere in large quantity help the movement of your troops.

In conclusion, the maximum size of your army is defined by the population and the wealth of the land through which you are travelling, other possibilities being viable only for a short period.

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  • $\begingroup$ Much of the weight of a cow is not edible meat, so you need to scale up your estimates some. $\endgroup$ – Oldcat Dec 22 '15 at 22:33
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If this question is about the size of armies that have marched ON LAND, then here is some detail.

Halagu Khan, grandson of the famous Genghis Khan marched down on the Muslim caliphate from the steppes of Mongolia all the way down to Egypt. The force he was commanding, however, could not be found accurately. Like his predecessors, he was more of a raider than a warrior.

Khalid Ibn Al-Waleed was the finest military general, any woman has conceived so far. Keeping his astounding victories in war aside, he is known to have crossed the desert between Syria and Mesopotamia (Iraq) where his army is said to have marched for 2 whole days without a drop of water. His force was smallish though (~30k men). You might want to read in detail about his military achievements. Some of them are purely fantastic. Ah, not to mention he never lost any single battle in his career.

Tamerlane was one hell of a military genius. His primary force was a very seasoned and skilled cavalry. He kept marching, sacking, looting and plundering places as far apart as Egypt on one end and Moscow on the other like a goblin. One of his longest military undertakings was to chase a very pungent and annoying Mongol pest in what is modern day Russia. He started that journey from India. His accompanying force was small (~30,000 cavalry only) but once you take a look at the vast empty expanses during mid 15th century and the hostile terrain, you'd start appreciating his accomplishment.

These were some of the lesser known examples which could have missed your eyes. Roman, Persian and Greek (Alexander) armies' march is a famous and well known thing so I don't think you need to be informed about them.

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Vienna siege (1529) featured an Ottoman army at least 120k strong (some say, 300k). The General Snow took the good care of them. As we know, the breakfast got cold.

Barbarossa committed about 100k men to the Third Crusade (1189).

Napoleon's primary failure was due to revolutionary French belief that good could be enforced. Unfortunately for him Russian peasants believed that their sorry state is an internal affair, which is to be settled internally.

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  • $\begingroup$ Can you give some citations, please? The sizes of armies and casualties in pre-modern conflicts are often greatly exaggerated; e.g., to make the winner look good. $\endgroup$ – user243 Sep 16 '15 at 23:28
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It seems "somewhere up to 100k" was possible in antiquity. Caesar had twelve legions (60k) at Alesia. Varro had 86k at Cannae. Alexander had some 40k at Issus.

Crecy had 30k French.

Napoleon split his force into several corps, in part for logistics.

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