You’ve formed up in your fighting order and begun to advance and first a cloud of light enemies (the velites) move up against you. Behind them, you can vaguely see the main Roman body, but not in much detail yet. Instead, you are treated to shower of lighter javelins; these only mass around 250g or so, but some of them are bound to catch a face or an unarmored leg and bring someone down or get stuck in a shield. The damage is probably minimal, but what the velites are doing is already wearing you down: you are now, physically and mentally “in combat”, with weapons flying and adrenaline running (whereas the Roman heavy infantry are not!). The velites don’t need to inflict casualties at this stage to have an effect: they’re inflicting friction (in the Clausewitzian sense, drink!) and that is enough.

As you approach the velites, they scatter back to their lines and now the first real trial comes: when you are about twenty meters out from the enemy line, a storm of those heavy pila come in, thick and all at once. Each one masses around 1.3kg (just short of three pounds) so even if the tip doesn’t bite, one of these things clanging off of armor or a shield is going to hurt, the impacts stagger men near you as you struggle to keep formation (and for a Hellenistic army, get and keep those sarisa-points down). The impact of the massed volley, especially against close-order infantry with tight fighting-width, is going to be chaotic as some men are killed, others disabled, still more suddenly staggered. The volley is followed almost immediately by the on-rush of the hastati. These guys don’t have a long spear for keeping you at a distance, they’re all brandishing swords and aim to get in close, using their large body-shields to absorb any blows you might throw while they get right up in your face, where their swords can stab and slash viciously over or under your shield. These hastati are aggressive and they’re probably better armored than you are.

And of course an engagement in contact like this is unpredictable. Perhaps in some areas, your lines push forward, whereas in other places it bends back. For large maneuver units (like taxeis!) this can be a real problem, but Roman maniples are small, so one maniple can advance if it finds the opportunity while others hold position or are even forced back (we actually see a general give, essentially, an “advance at your own discretion” order at Pydna, Plut. Aem. 20.8).

After a short and terrifying experience – these moments of shock combat probably didn’t last all that long, perhaps as little as just a few minutes – the hastati fall back. The front of your line is already physically and mentally exhausted. Many men are wounded and certainly some have been killed or disabled. I don’t want to oversell the casualties aspect of this: armies don’t annihilate each other in stand-up engagements (instead more casualties happen in pursuit), but wounds and exhaustion matter. Latin has this phrase, of being confectus vulneribus, “exhausted by wounds” or perhaps “worn down by wounds” (Liv. 24.26.14, 31.17.11, Caes. BGall. 5.45) to describe how the accumulation of a lot of little wounds can sap soldiers of their ability to resist effectively, even if no one wound is lethal. And just as important, all of the emotional impetus of your initial attack is spent. And there’s a decent chance that, as you try to breath, you still have these light velites‘ javelins (the hasta velitaris) thudding into your line every few seconds, because – again – they carry seven of them. They’re not out.

And then, as you are getting your bearings, trying desperately to catch your breath, the principes come up. They’re not physically tired or emotionally exhausted, but eager (like you were a half an hour ago when you advanced), they’ve been waiting all this time. Worse yet, these are probably the most combat-effective soldiers the Romans have, in the prime of their life, with years of combat experience. Now the second volley of pila comes in, creating yet more chaos. And then more angry, heavily armored Romans, behind their big shields, stabbing and cutting with their deadly gladii.

Now the men at the back of your single line may be relatively fresh, but you have no real way to get them to the front, so the wrath of the principes falls on men who are already exhausted, already wounded, already tired and already out of fight. Your line isn’t advancing so stridently; the men in the back, if the formation is deep, don’t know why the advance is slowed, why the line seems to be wavering, only that it seems to be wavering. And meanwhile, everyone is hoping that, at any moment, the victorious cavalry on the flanks is going to show up and win the battle, but they can’t see it anywhere in the confusion. Maybe your cavalry has won and is moments away – or perhaps Antiochus III charged it off the field again and no help is coming. Or perhaps the enemy cavalry has tied it up or worse yet, the Romans’ highly skilled Numidian allies might have mastered the flanks. You have no idea, you only know that help isn’t here, you are tired and more Romans are upon you. And somewhere, the thin thread of human courage snaps, either from the exhausted men in front or the confused men behind and the formation begins to collapse.

As the collective defense of lapped shields or serried pikes gives way, the Romans are now truly in their element: their large shields function just fine in individual combat and their versatile swords do as well. Lead by their centurions, the principes, with practiced and experienced skill, are finding the gaps, cutting as they go. As the formation crumbles, the velites can pursue – lightly armored, but well enough armed, backed up by the equites if there are any left.

You can see thus how this is a formation designed to wear down an enemy’s main battle line. It isn’t that the Romans are set massively deeper than a Hellenistic army, either. Assuming a base-3 set of file-depths (which seems to me the most likely), the Roman ranks are probably six, six and three men deep (hastati, principes, triarii), for a total depth over each file of 15, one less than the normal Macedonian formation. And with the wider fighting intervals the Romans use, they won’t normally have much of a problem matching the fighting width of the enemy army, unless substantially outnumbered (as, for instance, at Magnesia).

It’s not the Roman formation is deeper, it’s that its successive battle lines avoid exposing the entire army to exhaustion, attrition and friction all at once. In effect, it uses the same principles as defense-in-depth, exploiting the effect of friction on the enemy line to wear it down, but does so on the offensive. I don’t think it is an accident that when the Romans do lose, it tends to be because this model battle was spoiled in some way, either because the army was ambushed, enveloped, something disrupted the triplex acies or because the enemy was able to carry the field with just the momentum of the first charge – the Roman lines essentially failing like a building undergoing controlled demolition, as each floor pancakes the next without slowing.

But an army that isn’t able to decisively win the battle either at the first onset or somewhere else on the line is going to find itself in quite a lot of trouble as the Romans almost inevitably sandpaper away the morale and stamina of the main line of resistance until it collapses.

Now many of you may already be realizing that this kind of force is going to present a Hellenistic army with a lot of problems, both because it is set up for a different kind of fight than they are, but also because it may end up matching much heavier troops against the lighter parts of a Hellenistic army. But before we jump into battles, we need to zoom up to the upper levels of military analysis – operations and strategy – and talk about the advantages the Romans have there.

Because if all the Romans had was an edge in their tactical system, we might expect them to win battles but sometimes lose wars. Instead, while the Romans sometimes lose battles, they seemingly always win the war.

Bret Devereaux, “Collections: Phalanx’s Twilight, Legion’s Triumph, Part IIa: How a Legion Fights”, A Collection of Unmitigated Pedantry, 2024-02-09.