How the Roman Army Worked

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Podcast Transcript

For centuries, the Roman Republic and the Roman Empire were able to conquer and force their will on other people around the Mediterranean Sea.

The success of Rome was built on its army, and its army was able to sustain its dominance for so long because of its system of superior organization and logistics. 

It was this system which allowed them to excel in ancient warfare for so long.

Learn more about how Roman armies worked and what made them so successful on this episode of Everything Everywhere Daily.

Before I get into how the Roman army functioned, I should note that the Roman military was not a static thing. Rome, in its various iterations, was around for a long time, and during that time, there were changes that were gradually made in how the army was organized. 

Furthermore, army logistics differed depending on where the army was and what sort of environment they were in. How you scrounge food will be very different in a desert than it would have been in a forest. 

So, take this with a grain of salt. What I’ll be going over was typical, but not necessarily universal, during the Roman period. 

So, with that, let’s start with the organization of the Roman army. The base unit of the Roman military was the legion. 

A legion would have consisted of anywhere between 4500 to 5800 men, depending on the period. During the republic, there might have been 4200 foot soldiers and 300 cavalry. Later, during the imperial period, there could have been as many as 5,600 infantry and 200 auxiliary troops. 

Below the legion, there were cohorts and centuries. A legion with 4800 men would have had ten cohorts of 6 centuries, each consisting of 80 legionaries.

The organization of legions was standard, which allowed for legions to be quickly disbanded and merged with little interruption. If a legion had to be merged with another one, everyone would know their roles in the new legion. 

The legion commander was known as a legate, or in Latin, Legatus legionis. This was the equivalent of a general. 

During the Imperial period, there might have been a legate above that which was the commander of multiple legions. This would have been the Legatus Augusti pro praetore, or the Imedial Legate. 

Both of these positions were held by someone of senatorial rank. 

Beneath the legate would have been a younger man known as a Tribunus laticlavius. This person would have been second in command in a legion but not necessarily second in command during a battle due to their lack of experience. This was a position for well-connected young Roman men. 

Below that was the camp prefect, who was usually a veteran soldier of lower social rank. 

Below him were various lower tribunes, who were very young men just starting their political careers. They would have been given specific administrative roles.

Below that was Centurion, who did much of the actual work in a legion. They headed up the various centuries. The top centurion and the leader of the first century in the first cohort was known as the primus pilus. 

Each of the six centuries in a cohort corresponded to one of the lines they would form in battle. 

Second in command in a century would be the optio, and a century would also have a tesserarius, who was the guard commander. He oversaw guard duty and the distribution of passwords.

The smallest unit was the contubernia, which consisted of eight men. These men ate and slept together, sharing the load for carrying their collective gear. 

Beginning in 104 BC, every legion used an eagle as its standard. Every legion had a soldier known as the aquilifer who was responsible for the eagle and carried it into battle. 

Losing an eagle was an extreme dishonor, and soldiers in a legion took great pride in protecting their standard. 

Punishments were often handed out and could be quite severe. They could range from fines and demotions to beatings and even death. Soldiers sentenced to death would often be executed by Fustuarium, which was when their comrades would beat them to death. 

The equipment each legionary had was also relatively standard. You would get a helmet, shield, segmented armor, a spear known as a pilum, a short sword known as a gladius, and a dagger known as a pugio. 

After the military reforms of Marius, on which I’ve done a previous episode, the quality of Roman military equipment actually went down, as it now had to be mass-produced and provided by the state rather than each soldier buying his own gear. 

In addition to armor and weapons, each legionnaire had to carry cooking equipment, trenching tools, a cloak, and a limited amount of food. By and large, each legionnaire was responsible for carrying all of their personal gear. 

As far as food goes, the average soldier wouldn’t have been very well fed, at least in terms of the quality of food. About 60 to 75% of their diet consisted of grain, either in the form of bread or a gruel known as puls. Puls was often served with olive oil and salt. Later in the imperial period, cheese also became a staple of their diet. 

There would usually have been very little meat consumed, simply because of the cost of providing it for so many. 

The primary beverage for a soldier was a drink known as posca. It was a beverage made out of wine, vinegar, and water. The biblical accounts of Jesus being given vinegar on the cross was probably actually posca that was consumed by the Roman soldiers. 

Posca had a low alcohol content so it could hydrate without being intoxicating. Drunkenness was a serious crime in a legionary camp. 

Legions were designed to be mobile units. They could move from one place to another to counter threats as needed. 

Legionnaires, as I menioned before, were responsible for carrying their own gear. Their gear was mostly contained in a leather sack and hung from a pole known as a furca.

Their footgear was a type of sandal/boot known as a caligae.

In it they would walk on average 20 to 25 miles or 32 to 40 kilometers a day, depending on weather and terrain. Ideally, the 20 miles would be marched in 5 hours. 

Every single night, the legion would establish a camp when it was moving. A Roman encampment was no small thing. 

A team of scouts would usually ride ahead of the legion to find an open, level pace to for the camp. Once the troops arrived at the site, they would begin construction on the camp for the night. 

The camps were a standard design across all legions. Each camp was in the shape of a square. When the soldiers arrived, some would be put on guard duty and the rest would begin digging a trench around the camp with the dirt from the trench being used to create a berm. The trench was approximately three feet deep and five feet across. 

Each side of the square would have been about half a mile long on each side.

If possible, timber would be used to create a fence on the top of the berm. 

It is estimated that it took over 2200 men to set up the camp, and it could be done in 3200 to 5600 man hours, or just a few hours with that many people.

Based on what they actually spent their time on, Roman soldiers were more diggers than fighters. It was why they carried axes and picks along with their weapons. 

Legionnaires were always kept busy doing something, because they when they became idol, troubles would start.

There are several places around the world where you can still see the outline of these Roman camps, most notable is the near the Dead Sea, where the Romans besieged Masada. 

The next day, or a few days after, the camp would be broken and the process would start again. 

When a legion moved, it wasn’t just soldiers. There was actually a lot more to it. 

Using a somewhat realistic scenario, let’s say that four Roman legions needed to move from the lower Danube to the upper Rhine, a distance of about 1,600 kilometers or 1,000 miles. 

Each legion would have 5,000 men. In addition to transporting the soldiers, each legion would have 600 horses or mules to transport its siege weapons and other gear. All of the pack animals would require fodder if they didn’t want to spend a large part of the day grazing. 

Multiply that by four for all four legions. 

However, that is only part of the story. In addition to the Roman legion, there would probably have been an equal number of auxiliary and mercenary troops that traveled with them. 

In addition to that, there might have been double the number of non-combatants and camp followers. 

Roman soldiers were not allowed to marry, at least after the period when standing armies were created. However, that didn’t prevent women from following the legion and developing relationships with some of the men. These relationships were often overlooked for the sake of morale. 

Likewise, there would be merchants, slaves, and tradespeople who would follow the legion to perform services. Many people simply followed the soldiers to loot whatever they left behind from conquered enemies. 

So the total number of people who traveled when four legions had to move wasn’t 20,000, but it was probably closer to 100,000.

Populations were much smaller back then, and agricultural productivity was much less as well. One hundred thousand people marching through your region could be devastating if you had to provide all the food. 

Providing support for a legion was something that had to be done across the entire empire. Food, equipment, and clothing had to be transported, often across long distances, to support the troops. 

As you can probably guess, with the food and marching, not to mention the fighting, life as a Roman legionnaire was difficult. 

Who served in the legions and who was allowed to serve changed over time. 

During the first part of the republic, only Roman citizens who owned property were allowed to serve. 

After the Marian reforms, it was opened up to any citizen, regardless of land or wealth. 

Later, during the imperial period, this was further expanded as citizenship was expanded to everyone in the provinces. By the end of the Western empire, most people serving in the legions weren’t even Italian.

Service in the legion wasn’t a short-term commitment. Legionaries usually had to serve for 16 to 25 years and, if required, sometimes longer. 

The pay for a legionnaire was at first set to 225 denarii a year. This was eventually raised to 300, and eventually 500 as the currency was debased. 

There were also expenses for food and gear, which were deducted from a soldier’s annual pay. 

However, there were other possible upsides. If they conquered an enemy, soldiers would often receive some share of the booty that was captured. 

Also, many legionaries who served their full tour of duty would be given land in conquered territories where they could establish farms. 

For example, the town of Merida, Spain, was originally called Emerita Augusta, which meant the veterans of Augustus. The lands surrounding the city were given to men who served under Augustus. 

For a lucky few, they could rise through the ranks to have positions of authority within a legion. Perhaps not a legate or a tribune, but enough to earn more than the average soldier. 

Everything I’ve touched on in this episode simply deals with the organization and structure of a Roman Legion. I haven’t even gotten into how the Romans fought or the tactics and weapons they used. 

The rough system that I’ve described was one of the reasons why Rome was able to remain dominant for so long. Unlike many of their enemies, they had a system. They didn’t just do things willy-nilly. When the system ceased working, they changed it, like with the Marian Reforms. 

It was the Roman Legion system that allowed Rome to dominate the Mediterranean for over 500 years.