When we think of the Roman army then we usually think of a highly effective fighting machine. The core of that well-oiled war machine was formed by the Roman Legions, formations of up to 5.000 Roman citizens fighting as infantrymen.
But how did these Legions fight? And how did the individual Roman soldier fight?
Until 107 BC a Roman legion deployed in 3 lines that were less than 200 m (218 yds) apart. After the Velites (light skirmishers) retreated, the first line (the Hastati) attacked. They threw a volley of javelins (pila) at a distance of 15 m (16 yds) and 7,5 m (8 yds), then they drew their swords and engaged the still shocked and disorganized enemy. When they weren`t able to break the enemy the Hastati retreated behind the second line made up of the better armored and more experienced Principes who fought like the Hastati. If they also failed then the Triarii, the most experienced soldiers forming the third line had to engage. After 107 BC the differentiation into Hastati, Principes, and Triarii was dropped and soldiers were equipped more uniformly while maintaining the fighting style of the Principes.
Let`s find out!
The Manipular system & the Cohort tactics – 2 ways to organize a legion
While the number of soldiers within a legion remained somewhat equal the organization of a Legion changed around the year 107 BC as a result of the so-called Marian reforms that are generally attributed to the Roman general Caius Marius (who also served 7 terms of office as consul, more terms than any politician during the time of the Roman Republic).
Aside from other innovations like reducing the baggage train and eliminating age and wealth requirements for military service Caius Marius is also known for changing the Manipular system that Rome had used since the Second Samnite War (around 315 BC) to the Cohort system that was then used during the Late Republic and the time of the Roman Empire.
In the following, I will talk about how the Roman legion fought in the Manipular system to a greater extent since it is a little bit more complex than the way a Legion organized in the cohort system would fight. The reason for that can be found in the different weapons and armor that the three different lines of battle within a legion organized in the manipular system had compared to the more standardized equipment that Roman soldiers used after 107 BC when the Legions were organized in the Cohort system.
If you want to find out more about the differences in equipment then I would like to recommend you my article here.
But let`s now start by looking at how a legion fought when it was organized in a manipular system.
The manipular system – in use from BC 315 to 107 BC
The manipular system got its name from the maniple, the smallest tactical formation the Roman army knew until the Marian reforms in 107 BC. During the lifetime of the Roman writer (and major source regarding the military of the Middle Republic), Polybios a maniple, the smallest tactical unit in the Roman army consisted of 120 men and had a width of 18 m (19.7 yds) and a depth of -depending on the formation – 3-6 m (3.2-6.5 yds).
During the Middle Republic, a Legion consisted of Velites (lightly armored skirmishers who had the job of skirmishing before the actual battle began) and 3 groups of infantry which were armored to different degrees.
During the lifetime of Polybios, a Roman Legion consisted of 10 maniples (each 120 men strong) of Hastati, 10 maniples of Principes, and 10 maniples of Triarii (each at half strength at only 60 men). An additional 1.200 Velites (lightly armed skirmishers) and 300 cavalrymen put the total number of soldiers within a legion at 4.500.
For more information on the differences between Hastati, Principes, and Triarii (and why the Triarii were the only ones having thrusting lances instead of javelins) I would like to recommend you my article here.
When a Roman legion had formed its battle formation each legionary (just like each Macedonian phalangite) manned a space of 3 ft (0,9 m) in every direction. Unlike the Macedonian phalangites, Roman soldiers could loosen their formation extending the space each soldier occupied to up to 6 ft (1,8 m) in every direction.
The Hastati, Principes, and Triarii did not only differ in their equipment, but they also differed in the way (and the point of time) they were used in a battle.
Let`s take a look!
How did Roman battles work?
In most Roman battles the center of the battle was formed by either one or several legions (consisting of Roman citizens) while the wings were manned with auxiliary troops and troops that the socii (allies) provided. Here you can find more information on how Rome used an extensive network of socii to govern Italy without having to garrison most of the Italian peninsula.
The legions in the center of the Roman battle formation (the wings being manned with auxiliary and socii troops) were expected to break the enemy by putting enough head-on pressure on the enemy`s battle lines. Encirclements were not common.
In the following, I will focus on the troops in the center of the Roman battle formation, the Roman legion. But during the time of the manipular system, a Roman legion did not consist of somewhat uniformly armored men like that would be the case in the Late Republic.
Hastati, Principes, Triarii – the 3 lines of battle
Instead, the 3 groups of Roman infantry (not counting the Velites who were used as skirmishers) were the Hastati, the Principes, and the Triarii.
Those differed in equipment and experience. And these differences gave them different roles on the battlefield.
The first line of battle was formed by 10 maniples (120 men each) of Hastati, the second line by 10 maniples (120 men each) of Principes, and the third line by 10 maniples (at only 60 men each) of Triarii. The distance between these lines was usually much less than 200 m (218 yds). The maniples of the first two lines had gaps of 18 m (20 yds) between themself and the neighboring maniple while the Triarii formed one consecutive line.
The space between the individual maniples of the first two battle lines gave these units greater room to maneuver themselves into better positions and in case the situation presented itself it could be used to open up the formation to cover more ground so that the soldiers in the rear ranks of the line could also interfere in the fighting.
These individual tactical decisions were independently from the high command made by the senior of the two centurions who commanded the maniple (each maniple consisted of 2 centuries, each commanded by a centurion).
That degree of tactical freedom that centurions as leaders of a maniple had was unknown to most enemies of Rome and one of the reasons why the Roman army was so successful. Here you can find out more about the other reasons that made the Roman army so successful.
Ok, so there were three lines of infantry and a line of light skirmishers in front of them. But how did these three lines interact with each other?
How did the Hastati, Principes, and Triarii interact in battle?
While the Roman army positioned itself on the battlefield and the Hastati, Principes, and Triarii formed their lines the Velites, the lightly armored skirmishers, were already engaging the enemy.
The job of the Velites was to test the strength of the enemy’s formation by throwing javelins and to keep the enemy skirmishers from bothering the Roman troops while the main forces took positions. As soon as they were engaged by anything other than hostile skirmishers the Velites retreated through the gaps between the maniples of the first and second Roman battle lines.
During the actual battle the Velites would mostly aid in defending parts of the battlefield that could not be manned by heavy infantry (for example when there was a swamp or a group of rocks on or right next to the battlefield) or assist with taking care of the wounded.
As soon as the Velites had retreated the first Roman line of battle formed by 10 maniples of Hastati advanced on the enemy.
So normally I would now talk about how the Hastati fought, how they used their javelins to break up the enemy formation, and then finish them off with their swords, the Gladius. But as I mentioned, the 3 lines of battle were differently armored. And that had to do with how the 3 lines of battle interacted with each other.
Because of that, I decided to talk about how the Hastati (and also the Principes) fought in the next paragraph. For now, I would like to jump over the actual fighting part and begin with the usual situation that the Hastati had not been able to defeat the enemy force.
The Hastati, the first line of battle, were not expected to defeat the enemy. Instead, they were expected to fight for some time, weaken the enemy while keeping their casualties low, but then retreat and allow the more experienced and better armored Principes (the second line) to finish the job.
While the exact distance between the 3 lines of battle is not known we have one source talking about the distance between the lines at the battle of Zama where Hannibal was finally defeated. Sources indicate that the Roman lines at the battle of Zama were 200 m (218 yds) apart from each other. The source also mentioned that that distance was unusually large.
So we can assume that the Roman lines of battle were usually much less than 200 m (218 yds) apart from each other.
But back to why it made so much sense to send in the less armored and less experienced Hastati first.
By sending in the younger, less armed, and most importantly less experienced Hastati first you weakened the enemy while keeping the better armored and more experienced troops in reserve to finish the job. Now one might say, wouldn`t it be smarter to first send in the more experienced and better-armored men? And in case of a riskless victory that might very well be true. But in case of a hard battle, it was much better to first send in the less experienced men.
I mean just imagine you are a Hastati.
You are in your twenties you have a little experience but you are nowhere close to the experience (and the level of armor) that the Principes have. So let`s now assume that the Principes would have been sent in first and failed at their job. Then you, knowing that the enemy has just defeated more experienced and better-armored troops than you, would now have to try your luck…needless to say that that would not have been good for morale!
Ok, so the Hastati have done their duty. They have fought without suffering too many casualties. Here you can find out more about the combat mortality rate of Roman soldiers and how that rate drastically differed depending on whether the battle ended in a victory or a defeat.
As soon as the Hastati had done their duty they would retreat through the spaces between the 10 maniples of Principes that formed the second line of battle. These more experienced and better armored Principes were now expected to win the battle.
In case the Principes failed it was up to the Triarii, the most experienced soldiers to either win the battle or at least function as a barrier behind which the defeated Hastati and Principes could reform and then re-engage.
So to sum it up: The manipular system worked in the way that the enemy would be faced with three lines of gradually better armored and more experienced soldiers.
But how did the individual soldier fight? Let`s find it out!
How did Roman soldiers fight?
While the 3 lines of battle (the Hastati, the Principes, and the Triarii) drastically differed in the degree to which they wore armor at least the first two – the Hastati and the Principes – fought in a very similar way (that was also used by Roman legionaries after the introduction of the Cohort tactics in 107 BC).
The fighting style of the first two lines of battle was influenced by the Pilum, a javelin designed in a way it could not be thrown back at the Roman soldiers. While the Triarii who formed the third and last line of battle used a thrusting lance (hasta), both Hastati and Principes carried two pila (javelins).
As soon as the Velites had retreated behind the Hastati a signal, usually by a trumpet, was given and the 10 maniples of Hastati advanced on their enemy. The Principes in the second line of battle would follow them at a distance of less than 200 m (218 yds).
As soon as the Hastati (or Principes) were only 15 m (16 yds) away from the enemy they would collectively throw their first javelin, and the second volley followed at a distance of 7,5 m (8 yds). While the enemy formation was still shocked by the two closely followed volleys of javelins the Hastati (or Principes) pulled their swords and entered close combat.
And while the Hastati didn`t wear much body armor compared to the Principes and Triarii, their large shields, the scutum, that covered them from shoulder to knee still protected them pretty well. As a result, the mortality rate of Roman soldiers was relatively low, more on that here.
In close combat, the Gladius, a sword that was ideal for stabbing but could also effectively be used for slashing, was a brutal weapon causing severe wounds. Here you can find out more about the Gladius, its weight, and how (and against what body parts) it was best used.
As soon as the Hastati had done their job they retreated through the gaps in the second line of battle (as described above). Then it was time for the Principes to win the battle by using basically the same method the Hastati had used. The only difference was that the Principes were wearing shirts of chainmail, the so-called lorica hamata, making them even more resilient.
In case the Principes failed at breaking the enemy it came down to the third and last line of battle, the Triarii. And the Triarii, more on them, their age, and their social background here, were not only the most experienced soldiers, they were also differently armed and deployed.
Unlike the Hastati and the Principes, the 600 Triarii in a legion were armed with thrusting lances (hasta) and formed one continuous, usually 3 men deep, line.
It is assumed that they had two jobs.
First, they were the last line of battle that was only sent in when the Hastati and Principes had failed. But the thrusting lances and the deployment in one continuous line also allow speculations that these battle-hardened veterans might have also been there to prevent their younger, less-experienced comrades from fleeing.
And while that second job is pure speculation the first one is historically secured. There was even a phrase: The Roman saying „res ad triarios rediit“ means as much as now it is up to the Triarii (the most experienced soldiers forming the third and last line of battle) to win the day. It means that the last reserves had to be mobilized in a desperate situation.
So there we have it, the manipular system and how the 3 lines of battle interacted with each other. The manipular system was highly effective because the division into several maniples gave the army greater tactical flexibility than the phalanx could.
Here you can find out more about how the phalanx worked and the tactical limitations that were the result.
However, during the Marian reforms, the system of organizing the heavy infantry in 3 groups was given up, and while the names Hastati, Principes, and Triarii were maintained to mark the seniority of centurions the armor and weapons of Roman soldiers were standardized.
Aside from that the maniple as the tactical unit was replaced by the cohort that consisted of 3 maniples.
The Cohort tactics – used ever since 107 BC
On the turn from the Middle to the Late Republic, Rome was faced with new enemies. Especially Germanic and Gaul tribes troubled Rome, more on that here.
When faced with the tactics of Gallic and Germanic armies the maniples (tactical units of 120 men) proved too small. So the cohort, a tactical unit comprised of 6 centuries (= 3 maniples) and with an ideal strength of 480 men (1/10 of the entire Legion) replaced the maniple as the tactical unit in the aftermath of the Marian reforms in 107 BC.
Another result of the Marian reforms was that the difference between Hastati, Principes, and Triarii regarding the equipment was scrapped. Additionally, the age and wealth requirements for serving in the legions were also scrapped. Here you can find out more about the new requirements for recruits willing to join the Roman legions, the Praetorian guard, or the Auxiliary troops.
From 107 BC forward the Roman legionaries were (more or less) uniformly armored and equipped. Here you can find out more about the armor and weapons that Roman soldiers used after the Marian reforms.
However, the way the individual soldier fought remained the same.
When the Roman battle line was 15 m (16 yds) away from the enemy they threw their first pilum, a light javelin. After they had come even closer a second volley hit the enemy from a distance of 7,5 m (8 yds). After that, the soldiers, the so-called miles, drew their swords and entered close combat while the enemy formation was still disorganized and shocked from the two pila-volleys.
That system was extremely effective and the simplification into one somewhat standardized type of infantryman (the so-called „miles“) instead of 3 different groups of infantrymen certainly also helped.
As a result, the Roman army was a highly successful war machine. However, there were also several other reasons aside from the battlefield tactics that made the Roman army such a formidable fighting force, more on these reasons in my article here.
And here you can find out more about the diet that the Roman soldiers ate.
Take care of yourself because you deserve it. You really do.
Until next time
Johannes Kromayer: Heerwesen und Kriegsführung der Griechen und Römer (München 1963).