The intuitive and a touch clever method is to take normal human walking speed – around 3mph – multiply it by walking hours per day (maybe 8) and go with that. This makes intuitive sense, but if large army logistics made intuitive sense, they wouldn’t be hard, and as Clausewitz says (drink!) “War is very simple, but the simplest thing is very hard.” Logistics is very hard. So why don’t armies move at c. 25 miles per day?
So let’s think about – in very general terms – what needs to happen and in what order for a large body of infantry to march. Everyone wakes up and starts to get moving (probably around 5am). Breakfast needs to happen, which may require making fires. Tents need to be struck and stowed along with all of the gear in the baggage train and individual soldiers need to stow their own equipment. All sorts of small tasks add up to eat away parts of the morning. Then everyone needs to get gathered and ready to march.
And now – because you are a large body of infantry, you wait. Let me explain – let’s take a nominally full strength (c. 3,000 men) American Civil War brigade, marching on a road 13ft or so wide. You can get five men (a little cramped) into a single row on that road, meaning that the infantry itself stretches 600 ranks deep. Unlike in the movies (which love ultra-compact marching formations because it looks cool) you need a few feet of separation between rows for best effect (WW2 US Army guidelines specified 2-5 yards), let’s assume each soldier occupies about 5 feet in the marching order. So the infantry is 3,000ft long (914m; nine football fields). We also need unit separation (between the regiments, it’s important to avoid “accordioning” on the march and facilitate control; WW2 army regs suggested 100 yards between companies, 50 yards between platoons, so these could be quite large), so let’s round up to 4,000 ft (1219m; 13 football fields).
But we also have tents, food supplies, spare ammunition and all sorts of other of what the Romans would have called impedimenta (sidenote: if you are thinking, “well, but a pre-gunpowder army doesn’t need this; 1) arrows take up space and 2) camp entrenching supplies – the Romans marched heavy). How many wagons, pack animals or porters you need varies – the Romans seem to have often moved with a mule for every six-to-eight men, plus the army’s siege train. A good rule-of-thumb I’ve seen for American Civil War estimates is around 20 wagons per thousand, so 60 wagons. Rule of thumb in the ACW is 80 wagons to a mile of road, so our wagon train ought to take up around another 4,000ft.
(Sidenote: you can see why logistics gets complicated fast. Even in explaining a rule of thumb, I have to resort to rules of thumb, or else we have to inventory all of the stuff an infantry brigade needs, and all of the food they need and then parcel it out by wagons (and then figure for the mule-or-horse teams for the wagons) and on and on. Fortunately for the historians, this sort of work was done by the armies at the time and written down, so we tend to use their staff-work.)
So the entire force is probably a bit more than 8,000 ft long – 1.5 miles. In practice, there’s actually a lot more space eaten up in separation (between wagons, between men) so it would be longer, but I don’t want to get lost in the details. And this is for just 3,000 infantry – we have no cavalry with their many spare horses (three per man as a typical minimum) or god forbid a siege train which might involve hundreds of wagons.
Bret Devereaux, “New Acquisitions: How Fast Do Armies Move?”, A Collection of Unmitigated Pedantry, 2019-10-06.
February 19, 2022
QotD: Army marching speed in the pre-industrial era
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