Why Did the Legion Surpass the Phalanx as the Strongest Formation in Ancient Warfare?

Image credit: The Battle of Magnesia 190 BC. Artwork by Seán Ó’Brógáin © Osprey Publishing.

Up until 275 BC, the phalanx, a square of spearmen (and later, pikemen) in tight formation with overlapping shields, dominated the battlefield. Slowly, the Roman legion, relying on a combination of a huge shield and a short sword, chipped away at that dominance and finally overtook the phalanx to rule ancient battlefields until 378 AD, when the Battle of Adrianople heralded the beginning of cavalry supremacy and the dawn of medieval warfare.  

But why? How could a bunch of barbarians wielding what amounted to little more than a butcher’s knife overtake the formation Alexander the Great had used to establish the greatest empire the world had ever known?  

An artist’s rendition of a Hellenistic phalanx. Artwork by © Johnny Shumate.

The 2nd century BC Greek historian Polybius gives us a theory. He posited that the phalanx was too cumbersome and unwieldy, that its soldiers, while effective in a tight formation, were unable to handle combat that required them to change directions, or to work effectively on rough ground, or to fight as individuals if their formation broke apart.

In ideal conditions – flat ground with their flanks covered, the phalanx was unbeatable. But in battle, conditions are seldom ideal.  

Was Polybius right? This is the question I set out to answer in Legion Versus Phalanx. After examining six battles between the legion and the phalanx (Heraclea – 280 BC, Asculum – 279 BC, Beneventum – 275 BC, Cynoscephalae – 197 BC, Magnesia – 190 BC, and Pydna – 168 BC) here’s what I discovered:

1. Polybius was right, but he left a lot out

The Roman short sword was a weapon suited to both formed combat and individual fencing. The phalangite’s pike was only effective in a formed unit in good order. In a one-on-one fight, the pike was little more than a long broomstick.

Diodorus describes the famous duel between Dioxippus (wielding a short club), and Coragus (wielding a long pike), with Dioxippus closing inside the pike’s effective range to beat Coragus easily. Further, the phalanx could only fight in one direction – straight ahead.

The short sword makes changing direction simple. Wielding a 21-foot pike, even a simple 90-degree turn can cause weapons to get tangled, causing chaos. The massive Roman shield provided excellent protection for the mad rush that would be necessary for the Roman legionary seeking to get inside the effective range of the long pike to where he could deploy his short sword to maximum effect.

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2. Greater intervals allow greater flexibility

The Hellenistic phalangite usually deployed in 3-foot intervals. The Roman legionary deployed in double that space. This allowed the legion to deal with rough ground much more easily, walking around rocks, roots, or divots without breaking formation.

Further, far fewer soldiers were required to cover more ground, and the legion deployed in a checkboard of small units that could support and cover one another. The phalanx usually deployed in a single, lumbering line.

Reconstruction of the tactics of an individual princeps legionary. Artwork by Gerry Embleton © Osprey Publishing.

3. Roman generals actually, you know…generaled 

Alexander the Great was famous for deploying in the thick of the battle himself, fighting as a cavalry commander. This legacy continued among his successors, the commanders who deployed the phalanx in the six battles I examined. This makes sense when you consider a formation so unwieldy it could do little more than march straight ahead.

Hellenistic commanders tended to put their troops in place, then ride off to fight personally, abdicating field command. Roman generals certainly prized heroism in commanders (one of their greatest honours, the spolia opimawas given to a Roman commander for victory in single combat), but the sources clearly show the Roman tendency to command from behind the battle line, ordering and moving troops to respond to the dynamic and evolving nature of the battle.

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4. Distributed command and control

Roman armies cultivated and rewarded individual initiative at comparatively low ranks. The velites, Roman skirmishers, wore animal skins partly in order to make them visible to their officers, who could mark their individual acts of heroism.

At the Battle of Pydna, Roman centurions were able to exploit emerging gaps in the Antigonid phalanx, leading their troops in charges that brought them into the 2-foot sweet spot where their short swords would be effective and the Antigonid pikes would be useless, without requiring orders from senior officers.

The sources show no comparable initiative among Hellenistic armies, where the king was the ultimate authority. It’s possible this was an outgrowth of cultural norms – a Roman republican system where individuals may have felt a greater sense of ownership over fight, versus subjects of an absolute monarch.

Myke Cole is the author of Legion versus Phalanx: The Epic Struggle for Infantry Supremacy in the Ancient World, published by Osprey Publishing.