The length of service in the Roman army (Legionaries, Auxiliaries, and Praetorians)

While the battles in which Roman soldiers fought and the generals who commanded these battles are well known the circumstances under which the average Roman soldier lived are far less well known.

In the course of my series of articles about the lives of the average Roman soldier, I try to shed some light on these men who were so essential for the rise of Rome and who still get overlooked so easily. So today I would like to talk about the length of service in the Roman army, how it differed depending on the type of unit and how it developed over time.

For more information on the lives of the Roman soldiers, I would also like to recommend you my list with the other articles of that series at the end of this article.

Augustus was the first to create a standing army and to fixate the length of service. Between 13 BC and 5 AD, a Roman legionary served 16 years in active duty and 4 years in reserve, which was changed to 20 years of active duty in 5 AD, raised to 22 years of active duty in 6 AD, and reduced back to 20 years shortly after. Auxiliaries served 25 years while Praetorians only served 16 years. A general rule is that the higher the prestige of a unit the shorter time of service.

Let`s now take a closer look.

But before we look at the length of service during the time of the Roman Empire I would like to offer some insight into the much less regulated and fixated length of service during the time of the Roman Republic.

The Length of service in the Roman army until the end of the Republic

When it comes to the length of military service one can differentiate between the time of the Roman Republic that started when the Romans expelled their (Etruscan) kings, more on why they did that here, and the fall of the Roman Republic in 27 BC that coincides with the erection of the principate, the rule of Augustus.

During the early Roman Republic, military service was seen as the (unpaid) duty of every Roman citizen between the age of 17 and 46 who was wealthy enough to afford to buy his own weapons and armor. These men could be recruited for a total of 16 campaigns.

Now that had several benefits to the state like the low cost of maintaining a militia army in comparison to a standing army. But it also had severe disadvantages for both state and the individual soldiers. You can find out more about these disadvantages that would eventually lead to the ruin of the Roman middle class in my article here.

Long story short, due to impoverishment the number of wealthy Roman citizens eligible for recruitment declined throughout the Roman expansion. As a reaction, the army was opened to men who did not own their own piece of land and who were now depending on the state (or better their generals) to provide them pay (more on that here) and retirement (more on that here).

So over the course of the Roman Republic, the soldiers changed from militiamen to professional soldiers who were still only recruited for individual campaigns.

As soon as a campaign was over these perfectly trained soldiers would suddenly find themselves unemployed and without a home to return to. These veterans were actually one of the major factors in the fall of the Roman Republic since they could easily be manipulated by cunning politicians like Caius Julius Caesar (or Augustus).

So there was no fixed length of service for Roman soldiers during the time of the Roman Republic since soldiers were recruited for each campaign individually. During the early Republic, men could be recruited for up to 16 campaigns and later the professional soldiers would also enlist for individual campaigns to make a living.

It wasn`t until the rule of Augustus that started in 27 BC that the length of the military service was organized and fixated.

Now that obviously bears one question: Why was Augustus so keen on changing the army of the Roman Republic, professional soldiers who would only be recruited (and paid) for individual campaigns into a standing army that would even have to be paid during times of peace.

Why did Augustus introduce a standing army with a fixed length of service?

When we think about the question of why Augustus created a standing army instead of an army of professional soldiers who were only recruited and paid for individual campaigns we have to take a look at the time Augustus grew up in.

The late Roman Republic, the time during which Caius Octavius who would later be known as Augustus, grew up was shaped by Civil Wars. Not only did Caius Julius Caesar and Gnaeus Pompeius Magnus, more on how Roman names worked and what they meant here in my article, wage a Civil War, there were also other rebellions like the second Catelinarian conspiracy or prior to that the civil war between Lucius Cornelius Sulla Felix, more on the meaning of each part of the name here, and Gaius Marius.

All these wars and rebellions during the crisis of the Roman Republic between 133 and 30 BC could rely on a large base of unemployed and desperate veterans who could easily be convinced by promising them a solid retirement.

For more information on the retirement of Roman soldiers and why such a powerful instrument was left in the hands of the Generals and not of the Roman State I would like to recommend you my article here.

Augustus knew that to prevent another General from using unemployed and desperate veterans to rise to power (remember, that is exactly how Augustus himself rose to power) he knew that he would not only have to provide secure pay and a retirement to his soldiers but that it would also be smart to station them as far away from the centers of power as possible.

Because of that Augustus did not only create a standing army with a fixed length of service but did also station the bulk of the military in the border provinces. Apart from keeping the potentially dangerous armies at a safe distance that had another benefit.

To prevent himself from ending like his adoptive father Augustus did his best to not appear like the singular ruler of Rome (that he was in reality). Just like his adoptive father he refused the title of king, mostly for historical reasons, more on that here. But he also returned the governance over some of the provinces, to be more precise the secure provinces away from the borders to the Senate.

That had a massive benefit. By returning the rule over these provinces to the Senate Augustus made sure that the impression of him renewing the political system of the Roman Republic was kept up. But since the bulk of the military was still stationed in the border provinces that were governed by Augustus he still kept all the power in his own hands.

So he could pretend to have restored the political system of the Roman Republic, more on that and the institutions and offices within the political system of the Roman Republic here, while simultaneously having all the power.

But enough about the way that led up to the establishment of a standing army and the fixation of the length of service.

Let`s now actually look at how long a Roman soldier had to serve in the army!

How long did Roman soldiers serve in the army?

The question of how long a Roman soldier served in the army during the time of the Roman Empire is actually harder to answer than one might think. Not only are there several general problems (like a certain inaccuracy when it comes to birth dates of soldiers) that we will talk about later, the length of service also depended on the prestige of the unit. Additionally, the length of service also changed over time.

A general rule of thumb when it comes to the length of military service during the time of the Roman Empire is that units with high prestige like the Praetorian guard had a shorter military service than units with lower prestige (like the Auxiliaries or the navy). Additionally, the length of service increased over the course of the Roman Empire.

Let`s take a look at the 3 general types of units and their individual length of service and how that length of service changed over time.

How long did Roman legionaries serve in the army?

The legions were the backbone of the Roman army in both the time of the Roman Republic and the time of the Roman Empire. To be eligible for service in the legion a man had to be a Roman citizen, have a clean reputation (neither himself nor his father could for example be a slave merchant), and had to meet high physical and certain intellectual requirements.

Do you wonder about the extent of these intellectual requirements and the general process of the recruitment of Roman soldiers? You can find the answers in my article here!

Between the years 13 BC and 5 AD a legionary served 16 years in active duty and another 4 years as a veteran. These veterans formed a reserve and could be called upon arms in case of need. After the legionaries had ended their 16 years of active service and the 4 years in reserve they were called „emeritus“ (= he, who has finished his time).

In the year 5 AD, the 16 years in active duty and 4 years in reserve were simplified to 20 years in active duty and raised to 22 years in 6 AD.

In the year 14 AD every Legionary was expected to serve at least 20 years. But some of these men had actually served 30-40 years and that caused some unrest between these men with extremely long times of service and the men who had „only“ served 20 years. That especially caused displeasure since all men would receive the same retirement, more on the retirement Roman soldiers could expect and how it differed depending on the prestige of a unit in my article here.

After 14 AD the length of service in the Legions was briefly shortened to 16 years but was soon again raised back to 20 years. That was then raised to 23-26 years during the second century AD.

The reasons for why the length of service was raised is not known. But it seems possible that the high standards that were expected from recruits, more on these requirements here, became harder and harder to meet. And the longer soldiers served the fewer men had to be provided with a retirement which obviously also saved money.

So it is safe to say that a young Roman who enlisted could at let`s say the age of 20 could expect to spend most of his life in the army. That combined with the fact that Roman soldiers were prohibited from marriage, more on the reasons for that here, created a family-like bond between the soldiers.

And that bond that was further promoted by the living arrangements under which Roman soldiers lived and fought was the backbone of the high discipline that would distinguish the Roman army. For more information on how that high level of discipline was connected to the idea of the soldiers living in a military family instead of a real family, I would like to recommend you my article here.

So after talking about the Roman legions, units made up of Roman citizens, let`s now talk about the units that were not made up by Roman citizens and, because of that, had a lower prestige.

How long did sailors & auxiliary troops serve in the Roman army?

Both the navy and the Auxilary troops mainly consisted of men without Roman citizenship and, because of that, had a lower prestige (and lower pay), more on that here.

The transfer of legionaries into the auxiliary troops was actually a common punishment for minor offenses that did not justify the full extent of the harsh Roman military justice system. You can find more information about the different types of punishments and how these punishments in combination with rewards kept the discipline up in my article here.

Since Auxilary troops and the navy had a lower prestige than the Roman legions they, following the already formulated rule of thumb, had a longer length of service.

Under the rule of Augustus (27 BC to 14 AD), the soldiers of the auxiliary troops just like the sailors of the navy served 25 years. That was raised to 26 years in the middle of the first century AD. Emperor Caracalla who ruled from 211 to 217 AD raised the time of service to 28 years.

So the Auxilary troops (and the sailors and soldiers of the navy) had to serve a lot longer than Roman legionaries. Now one could think that since they served longer they would be rewarded with more pay and a higher retirement than Roman legionaries.

Well, not exactly. Not only did Auxilariy troops make less money while having to accept the same deductions from their pay like Roman legionaries, more on that here, in contrary to their counterparts the auxiliary troops would also not receive a gift of land or money but only the Roman Civil Right, more on that here.

How long did Praetorians serve in ancient Rome?

The Praetorian guard had the highest prestige of all the units in the Roman army. Coincidentally the Praetorian guard also had the strictest requirements to join, more on these requirements and how some of them were tied to the earliest stages of the Roman expansion in my article here.

Due to the high prestige of the Praetorian guard, the members did not only get higher pay and retirement than other Roman soldiers, they would also only have to serve for 16 years.

Here you can find out more about the pay of a soldier of the Praetorian guard and what kind of buying power his pay had.

So now we have taken a look at how different units had a different length of service and how that length of service changed over time. But I have mentioned that determining the exact length of service is actually quite difficult.

Let me explain…

Problems with the definition of the length of service

There are multiple problems when it comes to determining the exact length of service of a Roman soldier.

The first and most obvious problem was that the date of birth was rarely registered in the official Roman birth register. So when a man was recruited his age was usually rounded up to the next 5. For example, a recruit who was somewhere around 23 at the time he enlisted would be registered as 25 years old.

Additionally, recruitments were performed every year while releases from the Roman army were only performed every second year. That meant that some men had served their mandatory time but still were not released for another year.

For more information on the recruitment of Roman soldiers, I would like to recommend you my article here.

The next problem was that some soldiers were kept from leaving even when their time of service was over, we already talked about some of the soldiers of Augustus who served 30 to 40 years, while others were released before their time of service was officially over.  Both were usually connected to the current situation. In case of hard war and a lack of experienced soldiers, men were kept from retiring since they could not be replaced by similarly experienced soldiers.

So when we look at the length of service that has been presented in the article we have to remember that these numbers were not set in stone and could vary due to the mentioned problems with the determination of the exact length of service.

I hope you found our trip into the length of the ancient Roman military service interesting.

In case you want to find out more about the living conditions of the average Roman soldier I would like to recommend you the following two articles from my series about the lives of Roman soldiers.

The article here talks about the diets of Roman soldiers including the famous Posca, the drink that was handed to the crucified Jesus, while the article here talks about the reasons why Roman soldiers were not allowed to marry (and which alternatives these men had to marriage).

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

Until next time

Yours truly

Luke Reitzer


H.J. Höper: Alltagsleben römischer Legionäre (1985).

M. Junkelmann: Die Legionen des Augustus: Der römische Soldat im archäologischen Experiment (1986).