How Did a Legion of the Roman Army Function?


By Gregory S. Aldrete, Ph.D., University of Wisconsin Green Bay

Continuity and professionalism in the Roman army were not provided by senior officers but junior officers who known as centurions. Since they were promoted from the ranks, they were very experienced and were among the best soldiers.

This is a marble Roman artwork of 2nd century BC.
Most Roman legions were kept in shape by the centurions. (Image: Louvre Museum/Public domain).

Centurions: The Backbone of the Roman Army

Legates and tribunes – the top-ranked officers in a legion – were political appointments, and changed very rapidly in every legion of the Roman army. This meant that the centurions were the ones who ensured professionalism. There were 60 centurions in every legion of the Roman army, and there was a strict hierarchy of seniority among them. It went from the most junior to the most senior centurion who was called primus pilus whose literal meaning is the first spear. The equivalent of the centurions in the modern US army will be sergeants.

Centurions were the ones who got things done and provided training to men and supervised them. Each centurion carried a vine stick to show his authority although it was more than just a symbol. He would beat the soldiers with this stick if and when he was displeased with them. A well-known centurion had the habit of beating soldiers so hard that the stick would break, and then he would shout “Bring me another”. He was thus nicknamed “Bring me another.” His legion was part of the great mutiny of Rhine legions in 14 AD and during the unrest, he was lynched by his own soldiers who were resentful towards him.

Weapons of the Roman Army

Every legionary of the Roman army had two main weapons. The first was a gladius: the famous Roman short sword. It had edges on both sides and could be used to cut. But it was most deadly when thrust with an intention to cause deep lethal injuries. It had been made for close combat and had a design that can kill most efficiently. It was not a flamboyant type of sword and was not made to show off; on the contrary, it was most practical. 

Illustration depicting a Roman centurion.
Roman centurions were the true leaders of the legions. (Image: Charlotte Mary Yonge/Public domain)

Every legionary also carried two spears that were called pile. Their heads were made of narrow steel shafts so that they would bend after impact. This did not allow enemies to pick them up and throw them back at the Romans. During the battle, the legion of the Roman army would move to a close-range, would throw their spears simultaneously, and then take out their swords and move forward, and cut their enemies to pieces.

Discipline and organization were the reasons that the Roman military system was able to defeat much bigger armies which fought with much less coordination. The Romans fought as a closely-knit group where each member supported and protected the other instead of fighting as individuals.

A golden eagle on a pole was given to every legion. As eagles and thunderbolts were important emblems of the God Jupiter, this was a very powerful icon. The soldier carrying the eagle was known as aquilifer, and it was a post of honor that was most sought after. With the passage of time, these eagles became symbols for the legions themselves. A legion of the Roman army could not suffer a worse disgrace than letting the enemy capture its eagle.

For the religious rituals of the legion, the eagles along with the other standards acted as the focus. Whenever a legion was camping, these standards were put at the center of the camp, in front of the commander’s tent on a raised platform. The legion performed their prayers and sacrifices below them.

A number and a name were given to every legion of the Roman army. The name sometimes indicated the place where the legion was raised. For example I Italica, or the III Gallica. In other cases, legions were named the person who had raised the legion, like II Augusta. The names given to other legions were explanatory or frightening. For example the VI Victrix, ‘victorious’, or XXI Rapax, “predator”, etc.

Learn more about the Roman army.

The Marching Camp

A significant feature of Roman legions was the marching camp. When a legion of the Roman army was traveling through an uncertain land, every night the soldiers would build a detailed camp. A series of roads would be cleared. Two main roads would form a cross that would divide the camp into four quadrants. The other roads would be designed as a grid.

Roman surveyors copied the design of these camps while building new cities, and the origin of the street grid of many modern European cities can be traced back to these legionary one-night camps. A five foot wide and three foot deep ditch surrounded these camps, behind which was a six foot high earth wall.

Image showing punishment of decimation in ancient Roman military.
Decimation by clubbing was a common punishment for a legion that did not fulfill its duties. (Image: William Hogarth / Public domain)

Perhaps the most important feature of the Roman army was its discipline. Soldiers were expected to perform their duties above everything else. They were inflicted with harsh penalties if they failed to perform their duty. The death penalty was awarded for offenses like disobedience or falling asleep while on watch duty.

This is a transcript from the video series The Roman Empire: From Augustus to the Fall of Rome. Watch it now, Wondrium.

Punishment by Decimation

A particularly Roman institution that illustrates this attitude was called decimation. If it was found that a whole unit, whether it was a century or a whole legion of the Roman army, had not performed its duty, the Romans had a special method of awarding a penalty for this. One out of every ten men was selected to receive punishment by way of a lottery. These ten percent of soldiers were then clubbed to death by the rest of their colleagues.

This is the real meaning of the English word “decimation” which is often misused. The remaining soldiers were given the sentence of sleeping outside the camp and eating barley in place of wheat. Though it may appear shocking, decimation was actually carried out on multiple occasions, mostly when a unit was thought to have shown cowardice in front of the enemy.

The critical points of the success of the Roman military were its organization, discipline, and professionalism. It became a model for a number of armies in the future. 

Learn more about Rome’s first emperor.

Common Questions About the Legions of the Roman Army

Q: What the ancient Roman legions named for?

The ancient Roman legions were named descriptively, or for their places of raising, or for the people who raised them, or commemorated a victory or were just a ferocious name, such as Legio XXI Rapax, Legio X Equestris; Legio III Cyrenaica, etc.

Q: By which Roman legion was Jesus crucified?

It was an auxiliary unit named Cohort I Sebastenorum that crucified Jesus. It must be said that the auxiliary units consisted mainly of 800 non-Roman soldiers. They provided support to the Roman legions and were also known as Cohorts.

Q: Who was the top officer of a legion of the Roman army?

The leader of a legion of the Roman army was called a Legate. Usually, the emperor appointed a senator for this position. He held the position for 3 to 4 years although he could keep it for a longer duration also.

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