Bret Devereaux

This can work even in sparsely populated areas, if you can rely on local elites to gather up the food in advance of your arrival so you can roll in and pick it up without having to massively disperse the army. 7/21

If communities are unfriendly, you can do foraging - steal the food. Best done when the crops are ripe or nearly so in the fields. Wheat *plants* can't run away, but farmers carrying sacks of processed grain can - and they'll run into walled settlements you have to siege. 8/21

Taking fortified population centers can get you supplies, but only if you storm them - which is tricky. You need to be bigger enough than the settlement that you can just quickly build a ramp and roll on in, but not so much bigger that their stored food is trivial. 9/21

Finally, you have long distance transport, which basically only works if you are on a coast line with decent harbors, or a navigable river, *and* you have the coordination to get supplies from somewhere else moved to you in quantity. 10/21

And I do mean *quantity* - back of the envelope math suggests a single Roman legion (typically a sub-unit of a larger army) might consume 8.26 tons of food per day alone, which pops up above 10 tons when you account for fodder for animals. 11/21

So this ends up being a flexible playbook of common methods. The exact playbook may vary a bit one army to the next (one huge question that makes a big difference is, 'can your army harvest and then process and then bake raw grain?' or do you need bread made for you?)...12/21

But commanders in the field are constantly shifting the balance of methods to meet their needs. Given that ancient armies don't run out of food all of the time, they are also clearly engaging in long-term planning with rule-of-thumb assumptions that are fairly reliable. 13/21

Because, to be clear, this is a setup with relatively minimal margin of error. The limits of a pre-truck army's carrying capacity means that you can't carry more than a couple weeks supplies with you, so total collapse is never more than a few weeks away. Plan carefully. 14/21