Mercenaries in Ancient Rome – Everything you must know!

The Roman war machine was one of the most effective fighting forces of history and enabled Rome to rise from a small town on the banks of the Tiber river to a global power. But when we think of the Roman military, then we usually imagine the Legionaries and potentially also the Auxiliary troops. However, mercenaries are certainly not the first thing that comes to mind when thinking about the Roman army.

But did the Roman army use mercenaries? And to what extent?

Caius Julius Caesar already successfully used mercenaries during the Gallic Wars. His Germanic mercenaries, who served as cavalrymen, were extremely helpful when it came to ending the rebellion of Vercingetorix. Mercenaries were then used in large numbers in Late Antiquity since it was cheaper and easier to hire experienced mercenaries who brought their own equipment than to recruit, equip, and train Roman soldiers.

Speaking of the armament of a Roman soldier. Here you can find out more about the weapons and armor each Roman soldier carried.

But let`s now look at the use of mercenaries by the Romans and how the use of mercenaries changed over time.

There are reports about the use of mercenaries during the time of the Roman republic. One of these reports is called „Commentarii de bello Gallico*“.

The „Commentarii De Bello Gallico“* was written by Caius Julius Caesar himself. In these books, Caesar describes the Gallic Wars through his own eyes making them not only a great source for the question of mercenaries in the Gallic Wars but also allowing us to experience the Gallic Wars through the eyes of one of the greatest generals of all time. Here* you can find a translated version of Caesar`s original texts.

Caius Julius Caesar had recruited Germanic mercenaries from the lands east of the Rhine river during the Gallic Wars (58-51/50 BC). These men served as cavalrymen and were quite helpful during the crackdown on the rebellion of Vercingetorix.

Ok, but why did Caesar hire mercenaries as cavalry and not raise his own Roman cavalry?

Romans weren`t good horsemen. So they preferred to focus on fighting as heavy infantry and either hire their cavalry or recruit auxiliary troops who then served as cavalry.

Here you can find out more about the recruitment of both legionaries and auxiliary troops and why many non-Romans were keen on serving in the Roman Auxiliary troops.

However, during the time of the Roman Republic and the early Empire these mercenaries were still only hired to supplement the main forces. The bulk of the Roman forces was still made up of the legions and the auxiliary troops.

That changed as time went on. And in late antiquity, Rome had to rely more and more on hiring mercenaries instead of recruiting their own troops.

Ever since the end of the 3rd century AD, Rome was more and more forced to hire mercenaries instead of recruiting its own troops. One reason for that was that the number of potential recruits had gone down significantly as a result of the Crisis of the Third Century (235-284 AD). It was simply no longer possible to recruit enough soldiers for the wars at more and more distant borders of the Empire.

Additionally, it was also much cheaper and easier to hire experienced local mercenaries who even brought their own equipment than to recruit, equip, and train Roman soldiers who then had to be transported to distant battlefields. Hiring local mercenaries was simply easier and cheaper.

Do you want to find out more about the recruitment of Roman soldiers and the requirements a man had to meet? Then please feel free to check out my article here.

However, the large-scale use of mercenaries in late antiquity was a double-edged sword.

On the one hand, the mercenaries provided high combat power at a time when the Roman recruitment pool was no longer sufficient to satisfy the demand for new soldiers. On the other hand, the loyalties of the mercenaries were questionable and often changed in the worst moments.

A good example of that can be found when Emperor Theodosius I crossed the Alps in the late 4th century and marched into Italy to finish off his rival Arbogast.

Arbogast had ordered a unit of Germanic mercenaries to attack emperor Theodosius from behind. But instead of fulfilling their orders, the mercenaries preferred to negotiate with Theodosius. And as soon as Theodosius I had given the mercenaries the written guarantee that he would pay them a nice sum of money, the mercenaries left Arbogast and switched to Theodosius.

And that pretty much sums up the main downside of using mercenaries throughout history. But the use of mercenaries by other great generals is a story for another time.

Here you can find out more about the use of mercenaries in the army of Alexander the Great.

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

Until next time

Yours truly

Luke Reitzer


Caius Julius Caesar: Commentarii De Bello Gallico.*

James Clarckson: Migration, mobility and language contact in and arround the ancient Mediterranean (2020).*

Chris McNab: The Roman army: The greatest war machine of the ancient world.*

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