Uniforms, heraldry, flags. In a military context, these all serve the crucial purpose of communication. And if they seem like fairly primitive methods of achieving that, well, for most of history, primitive methods are all we’ve had.

When it comes to communication — whether that’s signaling to troops on the battlefield or sending a message to a different part of your force elsewhere — your options are fundamentally three: it can be visual, auditory, or written (a special case of visual). Touch and taste are far too short-range to be of any use, and while scent can theoretically travel farther, our olfactory senses are too poor to make much use of it. Even an alien species gifted with a better nose would face the problems of slow movement and dissipation over distance, reducing the signal’s utility.

Written communication is great in some ways, terrible in others. So long as everybody involved is literate, the message won’t get garbled in transmission: excellent! Unfortunately, it’s also vulnerable to being intercepted, altered, even forged outright. Prior to modern times, it’s also slow, being limited to the speed of whatever’s carrying it, whether that’s a guy on foot, a rider, or a pigeon (which, as Year Four discussed, only works in very specialized circumstances). Writing is handy for sending a message to another military detachment, but you’re not going to be able to use it to communicate with the guys currently locked in combat.

What about visual signals more broadly? Movies give us tons of examples of a flag being raised or waved to communicate with the troops . . . but those examples are often deeply flawed, with the same movement of the same flag having the magical ability to communicate whatever is needed in the moment. Worse still is the version where the commander just lifts his arm, and suddenly thousands of men know it’s time to march forward.

Visual signals only work if you can see them. Which sounds like an obvious statement, but now imagine that the flag — much less the raised arm! — is two, three, ten football fields away from you. (Doesn’t matter which type of football. The point holds regardless.) How well can you see it? Remember that battle lines can get extremely long when the armies involved are big; are your eyes good enough to pick out a bit of cloth half a mile or more away? Are you looking in the right direction when the signal goes out? What about when you march forward, and now the flag is behind you?

Flags and similar kinds of standards, like the Roman legionary eagles, mostly get used at much shorter range, to drive individual smaller units. Your standard-bearer is at the front of your group’s block, not the back; when the flag advances, so do you. When it stops, you stop. When it retreats, you retreat. (When it falls, you say oh shit. And then probably try to pick it up, or hope one of your buddies does.) It’s useful for moving a limited mass of soldiers around, but you can’t use it to transmit orders from the commander to that mass.

There are other visual ways to signal, e.g. by sending flares up into the sky, but you get the idea. Any such method is subject to these limitations on the battlefield, while over longer distances, you’re looking at the kinds of communication systems described in Year Eight. They are, generally speaking, blunt instruments at best, not capable of delivering complex information or instructions.

So what about sound? You won’t be surprised to hear me say this also has problems. Speech only goes so far; studies suggest that if you have a close-packed and quiet crowd and a good set of lungs, your voice might carry to a few thousand people, but “close-packed and quiet” does not describe battlefield conditions, nor communication at a distance. It’s a little unclear how long ago speaking trumpets (megaphones) were invented, but even those only boost your range a little.

Musical instruments do better, and they don’t require you to be facing them to receive the signal. As with flags, though, your “vocabulary” is limited, because relying on a complex melody to communicate “third unit of cavalry, circle around the army’s flank to intercept their reserves” is not so much courting failure as doing a swan dive into failure’s arms. It also turns out that, like flags, instruments have mostly been used to control the movements of smaller units: you’re only being cued to move if it’s your group’s horn or drum sounding the advance or retreat. (I presume, though I don’t know, that you know it’s yours because it’s loud enough to be obviously nearby, as opposed to farther down the field.) Once again, the commander can’t really use this to send orders from his post, because which group is he trying to signal?

Pretty much the only thing he can use is a messenger. Send someone on foot or on horseback with orders (written or verbal), and hope the messenger doesn’t get captured, killed, or ignored by the officer on the receiving end, who’s annoyed that some lackey claims he’s supposed to change his plans or move into action. There’s a reason we have that idiom about “don’t shoot the messenger” . . .

With all of this in place, you can see why modern technology had such a revolutionary effect on warfare. Telegraphs and radios, not to mention their later successors, mean that suddenly you can transmit your written or auditory signals vastly quicker — and that goes both ways! I’ve been talking as if everything is supposed to go from the commander to the troops, but he needs updates, too, and being able to send word more or less instantaneously that the center is collapsing or the right wing is about to be flanked opens up a whole new world of tactical responses.

Because if you were wondering how anybody managed when signaling was so crude and inefficient, the answer genuinely is “they kinda didn’t.” If your communication is limited, your control is limited. You deploy your troops for battle and then press play, with maybe one or two tricks held in reserve; everything else is up to the guys in different spots on the field, because there’s no way to manage more complex coordination and maneuvering.

But with every improvement in your signals, you acquire new options. Maybe your infantry units can not just advance, halt, and retreat, but wheel to face a new direction. Maybe you can tell in something like real time that your far-distant left is hard pressed, so you can dispatch reinforcements in time to do some good.

Which means that if you’re writing speculative warfare, the communications aspect is vitally important. Do they have telepathy? Flying animals with more capabilities than homing pigeons? Long-distance scrying or satellite surveillance? Teleportation? Anything that can transmit detailed information faster than a guy on a horse is a major advancement in tactical and strategic capability over most of human history. Meanwhile, the weaknesses of that method open up fascinating possibilities for trouble: can it be intercepted, altered, forged entirely? How can you use that to screw over your characters, er, I mean, make their lives more interesting?