Pre-modern armies certainly do demand a considerable degree of coordination. In film and even sometimes in video games armies clash together in a confused melee with friends and foes all intermixed at random. Indeed, I have been asked by students more than once “What happens when X type of soldier ends up in a confused melee?” and had to explain that the answer is “they don’t”. Because no one fights that way, at least not intentionally.

In a fight, after all, a combatant is extremely vulnerable to attacks from behind or in their peripheral vision, especially if they are focused forward on the foe in front of them. A confused melee would thus produce extreme casualties and produce them extremely quickly. But fighters want to survive their combats and their leaders would like not only to win the battle but to have an army at the end of it. Remember: the purpose of the battle is to deliver a siege: if you win the battle but with only a pathetic handful of survivors, you haven’t really won much of anything.

The battle line is the obvious solution: each fighter is only responsible for a few feet of frontage directly in front of them, a small enough area that they can focus on it visually and direct whatever shield or armor or weapons they have towards it, giving them a greater margin of safety. Adding depth to the formation (that is, increasing the number of ranks, that is a row of fighters right to left) both secures each fighter against the possibility of being flanked due to the death of the fellows to their right or left (as now they’ll just be replaced by the next rank moving up) and adds a morale reinforcement which we’ll come back to […] But now you have a formation that consists essentially of a large number of files (that is, a single row of fighters front-to-back) which need to move together to create that unbroken, mutually supporting front line so that no one is being attacked from many sides at once. Again, all of this is before we start adding fighting styles like pike-formations or shield-walls that are designed to excel in this environment (and fare poorly out of it).

As an aside, this is one dynamic that I find games like Mount and Blade or the Total War series that simulate individual soldiers struggle to get quite right. In most games the line of formation either remains almost perfectly rigid (think units on “pike phalanx” in Rome: Total War) or units the moment they come into contact form rough blobs of models all pushing forward. But actually you are going to have men in the rear ranks trying to keep their relative position to the front ranks so the formation neither holds rigidly steady nor dissolves but is going to almost flex and bend (and if you are lucky, not tear or break). This is only an aside though because we’re not well informed about these sorts of dynamics, so it is hard to speak about them in-depth.

But to fight this way now means that all of your soldiers (really here we are talking about infantry; cavalry must also be coordinated but in different ways and because they are often composed of elites that coordination may be produced through different training methods) need to move in the same direction at the same speed in order to retain that front line where they can support each other. Again, we are not yet to something like a shield-wall or a sarisa-phalanx which demands tight coordination; even in a rough skirmish line you need to get everyone moving together just to maintain that unbroken front. A break in the front, after all, would be dangerous: enemies filtering into it uncontrolled could then flank and defeat individually the members of the broader line (two-on-one contests in melee combat typically end in seconds and are very lopsided), causing collapse.

Now the good news is that if all you need an army to do is form up in a rough line a few ranks deep and then move more or less forward, the coordination demands are not insurmountable. We’ve already discussed using marching formations to create the line of battle so all you need is a way to regulate speed (since forward is a fairly easy direction for everyone). It isn’t quite ideal for everyone to simply self-regulate their speed by looking around (at least not for a contact infantry line; for missile-skirmish troops moving in a “cloud” rather than a line they can absolutely do that) because that will produce a lot of stagger-start-stopping and accordioning which at best will slow you down and at worst will eventually turn your neat line into a rough crowd – one easily defeated if it is opposed by a line of infantry in good order. Keeping everyone in the same speed can be handled with music: the regular beat regulates the footsteps. That can be a marching song or it can be an instrument (ideally one easy to hear).

We’ve talked about armies – or components of armies – like this. I’ve described hoplite phalanxes through much of the classical periods, for instance, as essentially unguided missiles for this reason: the general hits “go” and the line moves forward. Likewise a shield-wall formation like the early English fyrd doesn’t need to do complex maneuvers. And for many armies, that was enough: a body of infantry which either held a position or moved forward in a single line, in some cases with a body of aristocratic cavalry which might be capable of more complex maneuvers (that the aristocrats had trained in since a young age). And you can see, if your culture has armies like this, why the general might be focused on either leading the cavalry in particular or else being the motivating “warrior-hero” general – such an army isn’t capable of much command once the advance starts in any event. They haven’t trained or prepared for it.

Bret Devereaux, “Collections: Total Generalship: Commanding Pre-Modern Armies, Part IIIa”, A Collection of Unmitigated Pedantry, 2022-06-17.