5 Reasons the Roman Army Was So Successful

When we think of the Roman army, especially the Roman legions, then we usually think of a highly successful fighting force that turned a small city at the banks of the Tiber river into a power that controlled the Mediterannean. But while the fact that the Roman army was highly successful is widely known most don`t know the reasons for that level of success.

So in the following, I would like to point out the reasons that were responsible for making the Roman army so successful.

  • The Economic & Personal resources to overwhelm or at least outlast any opponent
  • Highly flexible & adaptable infantry tactics
  • The Centurions: Experienced officers with the freedom to make tactical decisions on their own
  • High levels of discipline thanks to a system of reward and punishment
  • Effective logistics & an extensive road network

You might have noticed that the weapons and armor that Roman soldiers used are not listed. The reason for that is that neither the weapons nor the armor that Roman soldiers used was exclusive to Rome. Instead, Rome had adopted the different parts that made up the armament of a Roman soldier from its former enemies. Here you can find out more about that.

But more on that in the following. Let`s now take a closer look at the 5 reasons that made the Roman army so successful!

The Economic & Personal resources to overwhelm or at least outlast any opponent

One theme throughout Roman history is the Roman ability to come back from even the greatest defeats and raise new armies (or fleets) until the enemy was defeated. The prime example of that is the battle of Cannae where the Carthaginian general Hannibal was able to annihilate an entire Roman army.

According to the ancient writer Polybios, 70,000 Roman soldiers lost their lives at the battle of Cannae. But while that would have been a decisive blow for most realms of history it wasn`t for Rome.

Instead, Rome raised a new army, and the general Publius Cornelius Scipio Africanus (more on why Roman names could get so long here) was able to bring the war to Northern Africa, defeat Hannibal at the battle of Zama, and end the Second Punic War.

Only Rome could quickly raise and equip new armies that won that war as well as many other wars (like the war against the Hellenistic warlord Pyrrhus). But why did Rome have such abilities?

Originally the Roman army was a militia that consisted of wealthy farmers and craftsmen who were eligible for participating in wars for a total of 12 years. Depending on their experience and their equipment (that they had to bring themselves) they were categorized into 4 categories of infantry. You can find out more about that here.

Through these wars, Rome managed to rise from a small city on the banks of the Tiber river to the hegemonic power over Italy. Here you can find out more about the steps from a small city to ruler over Italy.

And that is the point where it gets interesting when talking about Rome`s ability to raise new armies.

While a part of the land that Rome captured during its expansion was added to the Roman territory and settled with either Veterans or the urban poor, much of the land was organized differently and some of the conquered cities were even given Roman civil rights.

All these measures (like distributing parts of the conquered land to penniless families which made these men eligible for military service or making the inhabitants of conquered cities Roman citizens which also made them eligible for serving in the Roman legions) drastically increased the reservoir of potential recruits for the Roman legions. And even the inhabitants of defeated territories who did not receive the Roman civil right (which would have made them eligible for service in the Roman legions) were bound to fight for Rome through different alliance systems.

That allowed Rome to fully utilize the personal and economic resources of their former enemies to their own advantage!

Do you want to find out more about how that worked and what different ways Rome had to govern newly conquered territories without having to garrison them with regular troops? Then I would like to recommend you my article here.

So the expansion of Rome and the integration of defeated cities and territories into either the Roman territory (making the inhabitants Roman citizens eligible for serving in the Roman legions) or into military alliances drastically increased Rome’s reservoir of potential recruits.

But until the Marian Reforms of 107 BC, some level of wealth was still required apart from being a Roman citizen to be able to join the Roman legion.

That changed in 107 BC after long and costly wars had basically destroyed the Roman Middle Class that had provided the bulk of the Roman soldiers until then. Here you can find out more about how the expansion of the Roman republic was responsible for the destruction of the Roman Middle Class.

And here you can find out more about the mortality rate of Roman soldiers during that period and how the mortality rate differed depending on whether a battle was won or lost.

After 107 BC military service in the legions was opened to every Roman citizen independent of his wealth as long as he could fulfill the requirements. More on these requirements and the recruitment of Roman soldiers in my article here.

Alongside that new development, the weapons and armor that Roman soldiers used were also standardized (at least to a certain degree). But since most of the recruits were now penniless the weapons and armor had to be supplied by Rome.

By the way, you might have expected the superiority of Roman weapons and armor on that list. But especially during the Roman republic the equipment used by Roman soldiers didn`t really differ from the equipment that the enemies of Rome used. Instead, most of the weapons and armor roman soldiers used had been adopted by Rome’s enemies as the ancient writer Polybios states.

For more information on that, I would like to recommend you my article here.

It is however true that Rome was unmatched in the ability to provide large numbers of soldiers with somewhat standardized weapons and armor. That however needed a lot of resources in addition to a good administration. And these resources were available thanks to the expansion of the Roman republic.


The foundation for the personal and economical conditions that allowed Rome to either overwhelm or outlast any enemy was rooted in the expansion of Rome which resulted in a growing number of citizens and growing access to resources. And since the expansion of the Roman republic came at the cost of its neighbors one could say that as Rome’s economical and personal resources grew so did its neighbors’ resources dwindle.

That effect compounded over time and was actually one of the reasons why nobody (successfully) copied the Roman army. Here you can find out more about the other reasons for that and an example for one king who still tried to copy the Roman army.

Ok, so now we have looked at the personal and economic conditions that allowed Rome to raise new armies in case of devastating defeats. And while that reason had more to do with the general Roman mentality that made the Roman state so successful the second reason is rooted within the way the Roman legions fought.

Highly flexible & adaptable infantry tactics

The infantry tactics that the Roman army used developed over time but can roughly be categorized into two parts.

First, in the early days of Rome, the Roman citizens fought as Hoplites in a phalanx formation (which they had adopted from the Etruscans, their neighbors to the North who themselves had probably adopted it from the Greeks).

Do you want to find out more about when Rome adopted the Phalanx from the Etruscans, when the Etruscans adopted the Phalanx from the Greeks, and what formation the Roman army used before they adopted the Phalanx? Then check out my article here.

During the Second Samnite War the Roman army was reorganized into Maniples, smaller tactical units that allowed the Roman army more tactical flexibility than the rigid phalanx.

The reason Rome gave up fighting in a phalanx can be attributed to the rugged terrain of Samnium, the southern Italian region in which much of the conflict was fought and which was not suited for the rigid phalanx formation. Here you can find more information on that.

So the phalanx that was formed by one consecutive line of heavily armored infantrymen was broken up into smaller units, the so-called maniples that were commanded by Centurions who had a certain degree of tactical freedom.

I actually wrote an entire article talking about the Maniples and how a Roman legion fought so please feel free to check it out.

During the Marian Reforms of 107 BC, the manipular system was replaced by the cohort system since the maniple proved too small of a unit for effectively fighting the new threat that Germanic and Gaul armies posed. However, the way the Roman legionaries fought remained pretty much the same, more on that here. And while the ideal strength of a legion was put at 6,000 men in the Marian reforms that number was soon reduced.

Caius Julius Caesar preferred legions with a strength of 4,000-4,200 men. By the way, Caesar also preferred to not replenish his veteran legions with new recruits. He rather operated with smaller legions and organized his recruits into new legions so that they would not reduce the fighting value of these veteran legions. Each Roman general could choose freely how many men each of his legions should hold.

Let`s take a closer look at how a legion was organized in the cohort system for a better idea of why it gave the army greater tactical flexibility than the phalanx.

In the Cohort system, each legion consisted of 10 Cohorts. Each Cohort consisted of 3 Maniples, each Maniple consisted of 2 centuries and each Centuria was commanded by a Centurion. Each Cohort was commanded by the most experienced Centurion of the 6 Centuries that made up the cohort.

Organizing a legion (4,000-6,000 men) into 10 Cohorts that could each operate relatively independently from each other allowed for a much higher tactical flexibility and was much more suited for fighting on rugged terrain than the phalanx.

But no matter the number of soldiers within a legion, in both the Manipular system and the cohort system the key factor for the success were the centurions.

The Centurions: Experienced officers with the freedom to make tactical decisions on their own

The centurions were the number one reason why Rome could give up fighting in a phalanx and turn towards fighting in the much more flexible manipular or cohort system.

The smallest unit within a Roman legion was the century, a unit commanded by a centurion.

A cohort was made up of 6 centuries and in combat, the most experienced centurion of the 6 commanded the cohort. The most experienced centurion of the 10 cohorts was called the primus pilus (=first spear). He commanded the first cohort of the legion which was made up of the most experienced soldiers.

Additionally, the Primus Pilus also attended the staff meetings and acted as advisor to the legate who just like the governor of the province in which the legion was stationed was a politician.

Centurions were experienced soldiers who were usually promoted from the ranks because of their capacities. That made sure that professional soldiers who knew what they were doing were positioned on every level of the Roman military which in return allowed the centurions to have more responsibilities and tactical freedoms than their counterparts in non-roman armies usually had.

Needless to say that these men were highly valued by both the soldiers and the generals. Oftentimes the number of fallen and wounded centurions was used as a way to describe how hard a battle had been for the Roman side.

Apart from that the pay of a Roman centurion was also a lot higher than the pay of regular Roman soldiers.

A Primus Pilus, the highest-ranking centurion of a legion could even make 10-30 times the annual pay a regular soldier made. And the money a primus pilus received for his retirement was usually enough to make him a member of the Equites. Here you can find out more about the Equites and the only thing in which they differed from the senators.

Since centurions were promoted from the ranks because of their capabilities every Roman soldier could – at least in theory – hope to one day become Primus Pilus and rise into the highest circles of Roman society.

The chance for that kind of social rise was actually one reason for the success of Rome. Here you can find out more about that and how the son of a freed slave even made it to the position of emperor.

Additionally, the presence of high-ranking officers who had come from the ranks was also a constant motivation for the regular soldiers since the centurions were a vivid example of the kind of career that was possible in the Roman army.

High levels of discipline thanks to a system of reward and punishment

The extremely high level of discipline and professionalism that was expected of Roman centurions would also rub off on the men next to them.

Additionally, there was also a well-balanced system of punishments and rewards in place that helped to maintain discipline to the highest standards. I wrote an entire article about that elaborate system of punishment and reward (including examples for potential rewards and punishments) so I will not repeat it here but recommend you my article on the topic that you can find here.

So while the individual Roman soldier (especially during the time of the Roman republic when Roman soldiers were basically militiamen) was on average not a better warrior than his enemy he was usually more disciplined which was crucial for successfully fighting in formation.

Here you can find out more about how the individual Roman soldier fought within a Roman battle formation.

However, even the most disciplined soldier could not fight effectively without a sufficient food supply. And that brings us to the last reason that made the Roman army so successful.

Effective logistics & an extensive road network

The third reason for the success of the Roman army was effective logistics. Whenever a war was won the Roman soldiers would exchange their swords for shovels and would start building streets. Especially during the Early Roman Empire, the time when the Civil war was over, some legions who were stationed in peaceful provinces spent most of their time building streets and public buildings.

And some of the streets that these men built are actually still used today!

These streets did not only enable trade but more importantly connected the different parts of the Roman empire so that even large armies could quickly be transferred from one end of the Empire to the other. By marching on well-built and well-maintained streets the Roman armies could maneuver much faster than if they would have marched offroad. And the supply trains that supplied the Roman armies with everything the soldiers needed (like food) could also use these streets for more efficient transportation.

Here you can find out more about the diet of a Roman soldier and get a rough idea of how much wheat, bacon, and other foods had to be moved to supply a Roman army.

Now a successful army alone does not equate to the success of a state. However, the first reason why the Roman army was so successful, the integration of former enemies to utilize their personal and economic resources, was also a reason for why Rome itself was so successful. Here you can find out more about the other 2 reasons that made Rome so sucessfull.

Take care of yourself because you deserve it. You really do.

Until next time

Yours truly

Luke Reitzer


Johannes Kromayer: Heerwesen und Kriegsführung der Griechen und Römer (München 1963).

Nathan Rosenstein: Rome at War. Farms, Families, and Death in the Middle Republic (2004 Chapell Hill & London).