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A Roman legion and its general.

The Roman Legions: The Organized Military Force Of The Roman Empire

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There is no doubt that the magnificent and long history of Rome was to a large extent dependent on its strong and highly developed army. From its earliest emergence, through the Roman Kingdom, Republic, and Empire, the successes of Rome were always dictated by the skill and size of its army. And the most crucial development of that army were the Roman legions. From Britain and Gaul to Syria and Egypt, the expansion of Rome was built on the power of the Roman legions. For some citizens of Rome, a soldier’s career within a legion was a sure source of income. For others, it was a ladder to success and prominence through which even an emperor’s title could be gained. History has shown us that the Roman legions were a key part of all of Rome’s successes and downfalls, and that is exactly why we are going to examine the workings of this legendary military unit.

The Earliest Forms of Roman Legions

The term  legion has become a very common word to us all, but we rarely stop to examine its original meaning. In Latin, a legion was known as  legio, denoting a military conscription and levy, and ultimately stemming from the word  legere, to choose. The early history of Rome is not a clear as its later periods of development. However, even before the emergence of the Roman legions proper, the early army of Rome was fairly organized.

A Roman centurion leading his men into battle

A Roman centurion leading his men into battle. (vukkostic / Adobe Stock)

Up until at least the 2 nd century BC, most units were separated into groups of one hundred men, called the centuries. For military purposes, these centuries could be grouped together to form a disciplined and formidable force. The title of the centurion, a commander of such a force, survived throughout Roman history and dates to this early period.

It is clear from the very beginnings of Rome that Roman leaders placed a huge emphasis on armed forces. They were also clearly aware of the importance a strong army played in politics and diplomacy. For this reason, serving in the army of Rome was “advertised” as a life duty, and a distinguishing feature of every able bodied and honorable citizen of Rome.

The Roman legions came to the forefront in the period of the Roman Republic. With each passing decade, it became increasingly obvious that the Roman army was involved in larger military operations and more frequently. Rome expanded its borders most often through warfare, and thus its army developed quickly and grew.

In the earliest days of the Republic the entire Roman army was separated into two legions. That way each of the two consuls in office at the time could control one legion each. But this changed rapidly when a much larger number of men and legions were called upon in 494 BC.

The expansion of the Roman army legions in 494 BC occurred during the dictatorship of Manius Valerius Maximus. Under his rule the “ First secession of the plebs” was ordered and the three tribes neighboring Rome rose up in revolt. To deal with the threat of the revolting Volsci, Aequi, and the Sabines, the dictator raised ten legions, totaling close to 45,000 men. This is the first time that such a large number of men were conscripted for the Roman army. Consequently, Roman’s legions became an effective and reliable military organization.

The Honing of a Deadly Sword: The Legion Takes Shape

But all this was still in an evolving state. Legions were formed but for a short time only. There were the four original legions during the mid-Republic era: Legion I to IV, with two assigned to each of the two consuls. But when a new military campaign or a threat required a greater number of men, further legions were raised as needed. This conscription method can be considered an efficient and affordable way of structuring an army without having to pay extra soldiers in times of peace.

The types of units in a legion varied in each period of Rome’s history as the methods of warfare evolved over the centuries. Early on, the biggest focus was on the cavalry. Known in Rome as the Equites, the cavalry was considered the most prestigious and deadly of all units. Cavalry positions were often reserved for the notable and upper-class young men of Rome as a way to rise to prominence in both political and military circles.

The position of the light infantry, or the velites, was left to the poor classes of Rome and formed the big part of the early legion. Since Roman soldiers were largely responsible for equipping themselves, the velites could not afford proper equipment. Rome’s light infantry was great at skirmishing and ranged warfare, relying on light javelins. They were offset by the largest part of a legion, the heavy infantry. Heavy infantry soldiers would gradually evolve to be a crucial part of the legion, the picture of the Roman soldier that we all know today. The heavy infantry was mostly comprised of citizens who were neither high born nor poor, essentially the “middle class.”

Roman foot soldiers, carrying javelins, on the march

Roman foot soldiers, carrying javelins, on the march. (Manfred Richter/ Adobe Stock)

Being the largest group in a legion, the heavy infantry was classed by experience. The triarii were the veterans and the most reliable and tested troops, reserved for extreme situations. The principes were the second line in the battle and had moderate experience. Lastly, the hastati, made up of raw and inexperienced recruits with next to no combat experience, formed the front line.

Rome’s legions were famously reorganized during the well-known Marian Reforms. These reforms, which occurred in the late Republic period, resulted in the tactical and more evolved organization of army units. After the reforms, a legion proper numbered around 4,500 men in total and was separated as follows. At the legion’s core were the 10 cohorts, a primary Prima Cohorta and 9 ordinary ones, with an additional 500 cavalry soldiers. The Prima Cohorta was twice as strong, the core of other legions only had six centuries. A single century was comprised of 80 men, or 10 contubernia (singular contubernium). The contubernia was the lowest unit formation and consisted of 8 soldiers, 1 mule, and all the equipment they required. Each of the centuries carried its own standard or “banner”. This new legion formation was highly effective and easy to maneuver in the field. And it was these strategic advantages that made the Roman legions superior to other fighting forces. It also resulted in many victories for Rome.

The Permanent Roman Legions Created By The Marian Reforms

The Marian Reforms also introduced another crucial advantage for the leaders and citizens of Rome. A legion was no longer an “on demand” military force but a permanent professional military unit. The new legions were comprised of all classes of citizens, including the poorest ones. Thus, a military career became a viable option for poor men as a way to earn good pay and distinguish themselves. Furthermore, the Marian Reforms greatly increased the size of the Roman army, allowing it to field large forces at any time, and to lead military campaigns on several fronts.

However, this military system placed a big emphasis on individual generals and other commanders, whose reliability and popularity with the legion’s soldiers could give them an extra advantage in crucial moments. Thus, a legion had a lot of power that it could leverage even in political areas. The most famous example of this power is Gaius Julius Caesar, whose “Crossing of the Rubicon” and the subsequent Roman civil war were fully supported by the legions under his command, who were loyal to him first and the state second.

The reforms that Gaius Marius brought to the Roman army created the ideal image of a Roman legion that would last for a long time. This general and statesman introduced key rational and strategic changes that made the legion a highly effective military unit. Becoming a soldier at that time was a viable career choice and a sure way to Roman citizenship. Although the average length of service for a Roman soldier was 25 years, many nonetheless took up the call. Moreover, every legion career soldier could rise in rank through exceptional acts of bravery and courage. This evolved army organization, itself a highly developed system, was a huge part of the successes attributed to Roman army legions as the empire grew.

Each new legion had its own number, and its own name and symbol. Often, these symbols were related to a crucial achievement or event in the legion’s past. All of this gave each legion a certain “identity” and notoriety, making them famous and providing the men who served in them a great sense of honor and pride. During the Civil Wars, when Rome developed from a republic to an empire, some generals gave their legions their own number. This gave rise to twin numbers, and so-called Gemina legions. Augustus Germanicus, for example, commanded several Legio X’s. He later changed the number of his legions from 50 to 28 for political and economic reasons. That number shrunk further to 25 after one of the most disastrous defeats of the Roman army: the defeat at the Battle of the Teutoburg Forest.

The incredible range of weapons the Roman legions had at the Battle of the Teutoburg Forest, which was a disastrous defeat for Roman against the German tribes

The incredible range of weapons the Roman legions had at the Battle of the Teutoburg Forest, which was a disastrous defeat for Roman against the German tribes. (Carole Raddato from FRANKFURT, Germany / CC BY-SA 2.0)

The Worst Defeat in the History of the Legions

Also known as the Varian Disaster, the Battle of the Teutoburg Forest was an enormous loss for Augustus Germanicus and, by extension, the Roman Empire. It occurred in 9 AD, when the Roman general Publius Quinctillius Varus was foolishly led into an ambush by his own officer, Arminius. Arminius was a Roman citizen with Germanic origins who sought to betray the Romans. He led them into the thick Teutoburg Forest where the disastrous ambush took place.

Three legions – XVII, XVIII, and XIX – were utterly annihilated by a coalition of Germanic tribes. It was an absolute defeat and massacre that left a deep scar on the Roman army and the reputation of the legions. General Varus committed suicide when he saw the annihilation of his forces. And Augustus himself is said to have been so distraught upon hearing the news that he came close to a complete breakdown. He started hitting his head against a wall, repeatedly shouting: “ Quintili Vare, legiones redde!” (Quintilius Varus, give me back my legions!).

The loss of life for Rome was unimaginable that day. Close to 20,000 men lost their lives and many were sacrificed, alive, to the Germanic gods.

The Most Famous Roman Legions Under Julius Caesar & Augustus

As Rome’s borders expanded through the centuries, the conquered peoples gradually became assimilated and could become Roman citizens. This made the army multi-ethnic, and subsequently, the legions were nicknamed by the region from which they were levied. Julius Caesar notably created several legions to use against the Gauls in his Gallic Campaign. Below are the 28 most famous legions that were active during the rule of Caesar and Augustus.

1. Legio I Germanica
2. Legio II Augusta
3. Legio III Augusta
4. Legio III Gallica
5. Legio III Cyrenaica
6. Legio IV Macedonica
7. Legio IV Scythica
8. Legio V Alaudae
9. Legio V Macedonica
10. Legio VI Victrix
11. Legio VI Ferrata
12. Legio VII Macedonica
13. Legio VIII Augusta
14. Legio IX Hispania
15. Legio X Gemina
16. Legio X Fretensis
17. Legio XI Claudia Pia Fidelis
18. Legio XII Fulminata
19. Legio XIII Gemina
20. Legio XIV Gemina Martia Victrix
21. Legio XV Apollinaris
22. Legio XVI Gallica
23. Legio XVII Castra Vetera
24. Legio XVIII Castra Vetera
25. Legio XIX Castra Vetera
Legio XX Valeria Victrix
27. Legio XXI Rapax
28. Legio XXII Deiotariana

Caesar in the Gallic Wars from the Story of Caesar and Cleopatra tapestry series

Caesar in the Gallic Wars from the Story of Caesar and Cleopatra tapestry series. (Justus van Egmont / CC0)

Each of these legions was stationed in a different part of the, by then, enormous Roman Empire. Each legion was responsible for maintaining power on Rome’s borders, and preventing the incursion of barbarian tribes. They became permanent around the time of Augustus. Each legion had its own base and most of them were stationed on Limes lines - Roman military roads fortified with watchtowers and forts. Throughout the life of the Roman Empire, the legion became synonymous with its success and military prowess. The Roman legions remain to this day a textbook example of a high-functioning, highly efficient, and perfectly developed military unit.

From a military perspective, the Roman legions were almost perfect. But they eventually became a power to manipulate by would-be Roman emperors and power-hungry generals. The legions were often used in coups and as a powerful tool of asserting power and gaining leverage. Even so, they remained a vital component in the complex mechanism that was the Roman Empire, the key tool that helped it become one the most powerful empires in classical antiquity.

Top image: A Roman legion and its general.                         Source: vukkostic / Adobe Stock

By Aleksa Vučković


Keppie, L. 2002. The Making of the Roman Army: From Republic to Empire. Routledge.
Le Bohec, Y. 2013. The Imperial Roman Army. Routledge.
Various, 2015. History of the Roman Legions. Self Published.



Pete Wagner's picture

The question is, with their sudden emergence as a regional power, taking over, raping and enslaving, and renaming the ancient Greek gods, and having a more Persian look than the locals, was Rome established as actually a second Sumerian (black-headed people) colony?  They looked similar (unlike the aboriginal villagers), and their ruthless, war-like, power-lusting behavior was similar.  

Nobody gets paid to tell the truth.

Aleksa Vučković's picture


I am a published author of over ten historical fiction novels, and I specialize in Slavic linguistics. Always pursuing my passions for writing, history and literature, I strive to deliver a thrilling and captivating read that touches upon history's most... Read More

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