The Nitpicker’s Guide to Ancient Warfare: The Romans

By David Flin

This series of articles is the first draft of what will hopefully be a book published by Sgt. Frosty Publications

The Romans

Imperial Roman legionaries in tight formation, a relief from Glanum, a Roman town in what is now southern France. Photo by wikimedia user 'Rama' and shared under the CC BY-SA 2.0 fr licence.

This is one where everyone knows the military structure. The legions. The trouble is, things that “everyone knows” are often simplifications. This tends to be true here.

Hollywood portrayals of Rome tend to imply that Rome was a homogenous society. There are even some historians such as Niall Ferguson (who is notably not an historian of the Roman period) who make the rather absurd claim that Rome was originally homogenous, that this enabled it to expand, which led to it becoming diverse and hence weak, resulting in its fall. This is, to put it politely, unadulterated nonsense put about to push a current political viewpoint.

Rome began as a frontier town on the edge of several different cultures in Italy, and it immediately began to incorporate the culturally and linguistically diverse people of pre-Roman Italy into both its army and its citizen body.

The Romans conquered, subjugated, and incorporated a wide variety of people in a manner intended to wring the maximum military benefit out of the conquered peoples. The side effect of this was to filter into Roman society all manner of diverse peoples. In 212AD, the Constitutio Antoniniana extended Roman citizenship to all free people in the Empire.

Getting that little piece out of the way, we can turn to how the Roman society and the Roman military interacted. We start with the obvious fact that the military was centred around the Legions, a professional standing army.

Legionnaires served for 25 years; very different from the previous general practice of enlisting for a single campaign. In order to cut down on tendencies for legionnaires to desert or have strong local ties, they were sent far from their homeland. Inevitably, this resulted in the ties of cohesion being to the Legion.

Furthermore, being a professional army, it could have a standard of coordination and skill far beyond that available to part-time soldiers.

Almost immediately, an additional system emerged for incorporating non-Romans into the army. In addition to incorporating subjugated people into the legions and “Romanising” them, non-Romans were used, called auxilia (literally, helpers). These first appeared during the Civil Wars, with Julius Caesar placing heavy reliance on Gallic cavalry to support his legions. At first, the auxilia were a small part of Roman armies, but by 23AD, they made up half of the total strength of the Roman army. This proportion seems to have then remained constant.

At the end of their 25 years service, a Roman legionary received a parcel of land or its money equivalent, and often became a prominent member of society. Romanised.

That is the basis of Roman society and of the Roman army. It’s more complicated than that for both cases, but this isn’t a PhD dissertation.

We’ve got professional soldiers, in a legion far from home for 25 years, with status and Roman citizenship at the end of it. The cohesive force is clearly going to be towards the legion.

This was demonstrated most clearly in 69AD, the Year of Four Emperors. Galba, Otho, Vitellius, and Vespasian. The legions were instrumental in making each of these emperor, one after the other. Galba was acclaimed emperor by his legion in early April in a revolt against Nero, and became emperor in June 68AD. As emperor, he managed to upset a lot of his supporters, and was murdered in January 69 by Otho with the help of the Praetorian Guard. Otho became emperor.

Meanwhile, also in January, Vitellius had been acclaimed by the legions of the Rhine in January 69. He won the First Battle of Bedriacum in April. Otho committed suicide, and Vitellius was appointed emperor.

However, he only had the support of the German legions. Vespasian, legate of Syria, made a bid to be emperor, and received the support of the legions of the Danube. The Danube legions defeated the German legions at the Second Battle of Bedriacum and, in December, Vitellius was killed and Vespasian became emperor.

Not that this was the end of the civil war, as the legions fought amongst each other for another year. The civil war only actually came to an end because there was no longer any living alternative to Vespasian as emperor.

Which all went to prove that the legions were primarily loyal to themselves, not necessarily to the emperor. And, as Romanisation started to fade, they weren’t particularly loyal to Rome either.

That is the potential problem of a long-term, standing professional army. That is why regimes do their best to ensure that a professional standing army is strongly loyal to it. You get things like oaths of loyalty and awards and constant reminders of their duty to the state. It’s always a bad sign when a professional standing army takes an oath of loyalty to a specific individual rather than the state or an institution of the state.

The actual structure of the legion is well-enough known that it does not need to be explained here in detail. In brief:

The early Roman Republic found the Greek phalanx formation too unwieldy for the terrain of central Italy. Each maniple consisted of 120 men in 12 files and 10 ranks. Three maniples and supporting officers made up a cohort of 420 men. Ten cohorts made up the heavy infantry section of a legion, but 20 cohorts were usually combined with a cavalry force and other supporting arms to make an army 10,000 strong.

A price to pay

While a professional standing army is usually very efficient militarily, and is very effective at defeating much larger numbers of part-time soldiers, it comes with a price. That price is cost. The cost of equipping and paying the soldiers is significant, but is small in comparison to the cost of having a large number of “able-bodied men of fighting age” not be available for economic activity. To be fair, the legions did build roads and castles, but that is minor, truly trivial against the loss of economic activity that these prime potential workers are not doing farming or mining or breeding horses or trading or processing material or ...

The foregone economic cost of a professional standing army is significant, and the larger the army, the more significant the cost.

In addition to this, taxes will be required for the upkeep of the army. The larger the army, the greater the tax burden.

A large standing army is a luxury that only a very rich society can afford. This point needs emphasising. Without a rich economy, a professional standing army is an unaffordable luxury. A Saxon fyrdsman or a Viking raider, when not engaged in war, is a productive member of society. A Roman legionnaire, to all intents and purposes, isn’t.

Of course, this means that the society is wealthy, which means that it is attractive to raiders in poorer lands just beyond its borders. The society will have to either deploy significant defensive forces on the borders – making those forces isolated from the centre of the society and thus less connected with that society – or it can try and expand the border to bring the troublesome area under its control – which simply moves the border further out and requires more troops to defend it.

This is where the trope of an eternal Roman Empire, constantly expanding, falls apart. Expanding makes maintaining the empire harder; not expanding makes maintaining the empire harder. Sooner or later, something will give. A fall can be delayed, but not denied.


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David Flin is a writer and owner of Sgt. Frosty Publications. His books can be found there.