by Mollie M. Madden

We all know ‘an army marches on its stomach,’ but it’s not like Napoleon discovered something new. Vegetius (De re militari) and Sun Tzu (The Art of War) were well aware of this concept, as was Alexander the Great (Engels, Alexander the Great and the Logistics of the Macedonian Army, 1980). And it wasn’t news to them, either. Pre-modern military commanders knew this; they planned for this. They paid attention to logistics.

Fantasy writers should, too.

If you have an army (or a quest, or, really, anyone just traveling about in your work) you need to think about logistics and do the math. That’s right. Math.

First, though, you need to answer some questions about your world.

1. How much does a character need to eat, i.e., what does a full ration look like?
   1. Does this vary? E.g., does an elf need more or less food or water than a human?
   2. What does this ration look like? If your soldiers are vampires, a cartload of bread isn’t going to be very helpful. Is there a cultural prohibition against certain foods? Is there a lysine contingency in case the goblin divisions mutiny?
   3. How does the army get supplies? Are they purchased, stolen, levied…? How is this funded? If you were listening to Hermione, then you know we can’t simply conjure food or money.
2. How are supplies transported? (pack animals, carts, ships, dragons…)
   1. How much can the transport carry? Does the transport need to eat/drink? How much? Does the transport need crew (who also need food/drink)?
   2. Are supplies locally available? Has the populace already destroyed them?
3. How much does it cost to acquire the supplies? To transport them? Is one form of transport more cost-effective than another? Sure, dragons can probably haul a lot BUT how much does it cost to feed and care for them?
4. What are the physical capabilities of the characters? How far can they go in a day? What is the maximum speed? Answer the same for the means of transport.
5. How big do you think your army is?

Now that you have those answers it’s time to think about how big of an army your world can actually support.

Just as an example, let’s use humans. The average human needs the caloric equivalent of 3 lbs. of bread and half a gallon of water per day (obviously, a human should have a more varied diet, but let’s keep it simple for the math). Doesn’t sound like that much. How big is that army again? 10,000 strong, you say? That’s 30,000 lbs. of bread. Daily. It’s an army of vampires? Cool. Is the populace large enough to support 10,000 vamps sinking their fangs into it on a regular basis? If not, how do the commanders and quartermasters get supplies to the army?

Pack horses? Lovely. A horse needs 10 lbs. of grain, 10 lbs. of forage, and 8 US gallons of water per day. That same horse can carry about 250 lbs. (not including the pack saddle)—maybe it’s more or less than that in your world. Each day it carries supplies, it’s consuming them, too. If it takes five days to reach the army with the supplies, the horse will consume 50 lbs. of the grain it’s carrying and deliver 200 lbs. to the army, enough to feed 66 soldiers or 20 horses for a day. If the horse has to carry forage and water, however, it will consume all the supplies it’s carrying in 2.5 days. You have dragons hauling carts? The same questions apply, although now you’re asking how much the cart can hold. If the cart holds one ton of meat—don’t rely on the availability of fresh meat to feed your dragons—needs two dragons to haul it, each dragon needs 100 lbs. of meat per day, and it takes five days to reach the army, those dragons will consume half of the meat supply before reaching the army. The 1000 lbs. of meat the army receives will feed two dragons for five days.

Now, how far apart are the supplies and the army? Think about those dragons. What if it takes eight days to reach the army? The army will receive only 20 percent of the cart’s original load, i.e., 400 lbs. of meat. Enough to feed two dragons for two days. How much does dragon transport cost? Does your army have that kind of cash?

If you’re thinking I don’t have armies, this doesn’t apply to me, let me ask you this: Do you have merchants transporting goods? Does anyone travel for pleasure or business (think medieval European kings going on royal progress)? Do you have a small group on a quest? The same questions apply, just on a different scale.

That’s all very interesting, you say, but this is fantasy. True.

Does your world have a magic system? It has rules, right?

Logistics are the supply system of your world, and the real physical needs and capabilities of characters and transport are the rules and boundaries. Establishing these basic realities, and then working within them, will strengthen the world-building and ground the reader in the physical aspects of the world. One of the fastest ways to knock me out of the story is to have an army of several hundred thousand and not a hint of how it’s being supplied and/or paid. You don’t need to spend pages describing the carrying capacity of dragon-drawn carts, but show me the carts—someone please write something with an army supplied by dragon-drawn carts!—and understand how your supply system functions. Like the majority of your world-building, the reader will never see most of this work. The reader doesn’t (necessarily) need to know the airspeed velocity of laden swallow, but you do.

•••

Mollie M. Madden holds a Ph.D. in medieval history from the University of Minnesota and researches fourteenth-century military logistics. Her recent publications include The Black Prince and the Grande Chevauchée of 1355 (Boydell & Brewer, 2018) and “How to succeed in a Chevauchée—The Black Prince raids in France in 1355” (Medieval Warfare Magazine, Aug/Sept 2019 issue). She currently works at a small liberal arts college and lives in rural North Carolina with her husband and three kids. When not working, writing or getting breakfast (second breakfast, elevensies, luncheon, etc.), she runs and is currently training for a half-
marathon. She doesn’t tweet, didn’t have Facebook until 2015, and still has a flip phone.