Let us assume, picking up our discussion of information last time, that our army is formed up into its battle array (pre-planned the night before, recall) and is advancing and our general has just now noticed something that demands a change in the plan. It could be a dangerous enemy attack (perhaps on the flank) or an opportunity to split the enemy line. Whatever it is, our general needs to make some alteration to the battle plan. It is almost certainly a fairly minor alteration, as with a battle line anywhere from a kilometer to several kilometers long, it would, for instance, take far too long to shuffle the right-to-left order of the line just due to the marching time involved. Nevertheless, the general needs to issue an unplanned, on-the-spot command; how does he do it?

The first option, of course, is shouting. The problem here is obvious: how is the commander’s command to be heard? Interestingly, there has been a fair bit of research by ancient historians looking at the question of how many people can possibly hear a short address unaided by modern loudspeakers and the like; figures vary but generally a few thousand if they are reasonably compact and quiet. That might work for a general’s pre-battle speech, delivered before the army advances, but it will not do for an army that is already in motion, much less once the chaos of battle has begun. Thousands of men marching (let alone fighting!) are noisy!

The modern solution to this problem is radio, but of course that’s hardly available to our pre-modern commander. Instead, to judge by films, the mind quickly jumps to signal flags. I am reminded of Braveheart (1995)’s rendition of the Battle of Falkirk, where Edward I uses signal flags to order his archers forward. HBO’s Rome also does this in its version of the Battle of Philippi, with flags being jostled and then pointed forward to signal the advance. Unfortunately, signal flags – as distinct from unit flags (which we’ll come back to in a moment) – have a few key problems, the most notable of which is that no one will be looking at them: after all the army is advancing, the soldiers are looking forward but signal flags (again, as opposed to unit flags) are going to be behind them, not placed out in the middle of No Man’s Land between the armies. As a result, signal flags are useful for sending information long distances (in a chain of stations or operators), for instance from one commander at distance to another, but not in battle; operational, rather than tactical tools. In practice, the use of signal flags like this is confined to the modern era; the first successful “optical telegraphs” (as iterations on things like smoke signals and fire relays) date to the late 18th century.

Unit flags – a banner or other big, obvious symbol (like a statue of an eagle on a stick) – are more useful. These can be positioned at the front of a unit, typically at its center. If it advances, then the soldiers in the unit also know to advance, following the standard they can see (because it is elevated, large and visible) even if they cannot hear the orders. There are two complications here though: first, the unit banner or flag is a relatively late innovation in antiquity, really only coming into its own with the Romans. The Achaemenids may have used some kinds of ensigns or standards, but the Greeks do not seem to have done. Instead our first really good documentation of something like a battle flag comes from the Romans: each legion had a signa (eventually standardized to the legionary eagle, the aquila), which was a shiny metal statue mounted on a pole so it could be easily seen. Units of the legion broken off to do other things might instead follow a less impressive cloth banner, a vexillum, by which such detachments became known as vexillationes. But the broader problem is that of course your general may not be particularly close to your flags (or other standards) which are generally at the front-center of each component unit of your army. The flags may allow a subordinate officer to “drive” the unit over the battlefield – and that’s good – but it doesn’t let the general tell that officer what to do.

A better option is music, but once again development seems to come fairly late in antiquity. Greek hoplites seem to have advanced to the music of the aulos, a double-reeded flute-like instrument; given the limitations of the instrument it is generally assumed it was used to keep time (so everyone marched in step) not transmit orders. Once again, a more complex system of musical signalling seems to come with the Romans, at least as detailed by Vegetius. Vegetius (2.22) notes three different kinds of horn instruments used by a legion: the tubicen was used to sound charge and retreat, the cornicen regulated the movement of the signa (so “advance” or “halt”), while the buccina was used mostly for camp signals: sounding watches or assemblies. It’s a system that is akin to later bugle calls, but note that the orders it can give are limited to a relative handful of prearranged signals: advance, halt, charge, retreat, assemble, change shift and so on.

The attentive reader here may have already noticed how developed Roman command and control is and may suspect that ties in with the Romans having a more “command” oriented culture of generalship; if so you are ahead of the game!

Of course if those instruments are sounding on a per-unit basis (and they are) that means you still have the problem of getting the order from the general to the instruments for the unit in question. And fundamentally here, the technology is – as I tell my students – man-on-horse. The particular fellow on the horse may be a dedicated messenger (if your military organization has those) or a subordinate officer or it may be the general himself.

But it is important to note now the limitations of this sort of system and we can use what we know of the Roman command and control system (as noted, one of the more developed of such systems prior to gunpowder) to get a sense of them. Let’s say the general realizes there is a problem on his flank and he needs a unit (probably here we’re talking a cohort or a maniple, not a legion) to change what it is doing. First off, the order needs to get within shouting range of the unit’s commander (in this case a senior centurion). The general can either go themselves or send a messenger; both options have their downsides. If the general goes himself he is essentially removing himself from observing or commanding the rest of the battle, but a common problem with sending a junior subordinate is that the unit commander may not respect or feel the need to obey that subordinate (written orders can help with this, but now we’re bringing in questions of literacy). Of course both a messenger or a general in transit may also well be killed, which will prevent the order from being received!

In either case, the message is going to move at galloping speed, which is around 40km/h, meaning that it may take several minutes for the general or messenger to navigate to the spot. That doesn’t sound so bad, but battles with contact weapons do not typically go for hours and hours; Pydna (168) was, as noted last week, decided in about an hour total! Of course a battle might be longer (or shorter!) than this, though much of that extra time is likely pre-battle skirmishing – the actual direct press of infantry formations in shock rarely lasts long because of the terror of it (and to a lesser extent its lethality; we’ll return to the balance of terror and lethality next time). Imagine if you were playing a Total War game and your input delay was, say, five minutes long in a battle that might only last an hour or two.

But of course galloping time isn’t the end of it. The message now has to be conveyed to the unit. In the Roman system, that means the messenger needs to find the appropriate centurion, explain the order to him and then ideally that fellow will then signal the instruments and signa to act accordingly – but even then, those instruments and signa only have a handful of prearranged signals available. Anything more complicated will need to be shouted down the line the old fashioned way (as we know, for instance, the Spartans did for lack of almost any of the rest of this apparatus of command, Xen. Lac. 13.9). Needless to say that means that giving any complex order to a unit already engaged or about to be engaged is going to mean starting by signalling retreat and then attempting to regroup the unit; regrouping an already retreating unit is one of the most difficult tasks on a battlefield and is rarely performed successfully in an unplanned fashion (even in a planned fashion it goes wrong as often as it goes right).

(This is, by the by, why reserves are so important. An unengaged unit hanging behind the lines can be given new orders far, far easier than a unit that is already engaged or about to be. And indeed, those familiar with the Roman system of fighting with its three lines of heavy infantry will note that it is a system heavy on reserves. Indeed, the manipular legion essentially assumes it will be necessary to retreat and regroup the first line of heavy infantry (the hastati) behind the second (the principes) and plans and drills for that. Note how the Roman command culture, the Roman fighting method and the actual apparatus of messengers, signa, instruments and junior officers all align here – that’s common because these sort of institutions tend to co-evolve.

By contrast we may compare a Greek hoplite army in the Classical Period. It has no battle flags or ensigns and the general is expected to fight on foot. In the past I’ve described the resulting phalanx as an “unguided missile” and this is a big reason why. That’s not to say hoplite generals never exerted command on the battlefield – better generals might keep a reserve to be rushed to important points (as Pagondas does at the Battle of Delium in 424 BC). But for the most part, once a hoplite general formed up the army and hit “go”, they had very little control over the army.

Bret Devereaux, “Collections: Total Generalship: Commanding Pre-Modern Armies, Part II: Commands”, A Collection of Unmitigated Pedantry, 2022-06-03.