Military capacity of the Roman Republic

Hello everybody,

I'm currently making some research for a timeline where the Gallic Wars end very badly for Caesar. I'm wondering how many Legions Rome could realistically muster to bar Vercingetorix from entering Italy, and/or attempting to retake Narbonnensis Gaul.

At this point (52 BC) Caesar had 12 Legions at the battle of Alesia (raised either from Italy or Hispania, if I'm correct). If we assume those are lost, and we add the 7 Legions Crassus lost the year before in his disastrous expedition against the Parthian, who is left to fight?

My guess is, they should be at least 2 Legions ready in Italy, because it's what the Pompey and the senate had when Caesar crossed the Rubicon. But I also found that up to 50 legions were raised by the various protagonist of the civil war (sometime for a very short period, and probably not very well trained, I suppose)

What do you think?

PS: if needed, we're talking about post Marian reform legions, so from 5200 to 6000 soldiers, depending on the number of auxillia.

This book should have the information you need:

https://www.questia.com/library/119072043/italian-manpower-225-b-c-a-d-14

I'll check that, thanks a lot. I'm nearly done with the first part of the TL.

Depends on what sort of time scale you are talking about. Legions, especially useful Legions couldn't be conjured out of thin air. So the Civil War total of 60 Legions would take years to be reached no matter how dire the situation. That said there were enough discharged veterans around and enough eager teenagers that Rome could easily have assembled 7 or 8 Legions of decent quality very quickly if a threat arose.

Thoresby said:

Depends on what sort of time scale you are talking about. Legions, especially useful Legions couldn't be conjured out of thin air. So the Civil War total of 60 Legions would take years to be reached no matter how dire the situation. That said there were enough discharged veterans around and enough eager teenagers that Rome could easily have assembled 7 or 8 Legions of decent quality very quickly if a threat arose.

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And even then, we have no reason to believe they were 60 full strength legions. Most of them were likely at most half strength.

That has the problem that the Gauls were mostly unarmored, the biggest problem imaginable because the Gauls got cut up alot more than the Romans in combat.
I should point that wearing armor was hot and annoying; I've worn chainmail in mock battles.

Maybe if you have the Gauls realize as early as you could, the score could change.

The Gauls won and sacked Rome because the Romans had a neocon elected whom worked even worse than our Shrubbies for us.

slydessertfox said:

And even then, we have no reason to believe they were 60 full strength legions. Most of them were likely at most half strength.

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You're wrong on that. The Romans frequently merged units in order to bring them up to full strength, for example at Philippi we know that of the Liberators two Legions were at full strength and they had just over 80,000 men spread among 17 Legions suggesting an average of 4750 which is not much short of the 5,120 that was a the ToE strength of a Legion at this point.
In fact at the time of Philippi we have a combined total of 36 Legions in Greece, another 8 Liberator Legions in East, another 9 Triumvir ones in Gaul and Spain plus 2 Legions in Italy and "some troops" in Africa, probably about a Legion in total but spread out. So in total at that moment there were 56 Legions under arms. Let's say that on average they were all a bit under strength at 4750 like the Liberator Legions at Philippi and you are looking at 266,000 Legionaries Republic wide.
Add to that the in Greece there were an additional 50,000 Auxiliary horseman and an unknown number of Auxiliary foot soldiers and archers but possibly 100,000 in total for both sides. All the Legions around the Republic would also have had attached Auxiliaries so on the same ratio as in Greece you're talking about 75,000 Auxiliaries in the rest of the Republic.
So 266,000 Legionaries, 150,000 Auxilaries in Greece, 75,000 in the rest of the Republic and you have a total of just under 1/2 a million soldiers across the Republic. Now that's two years after the murder of Julius Caesar caused a remobilisation but it shows you roughly what the Late Republic was capable of.

When Caesar entered Italy in 49 BC, he immediately recruited 14 legions (XVII-XXX) for the upcoming Civil War to add to the 12 (V-XVI) he had under arms at that point.

So it was evidently possible to quickly raise new forces in Italy during that timeframe.

jkay said:

The Gauls won and sacked Rome because the Romans had a neocon elected whom worked even worse than our Shrubbies for us.

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Talk about your anochronisms.

Depends on what sort of time scale you are talking about. Legions, especially useful Legions couldn't be conjured out of thin air. So the Civil War total of 60 Legions would take years to be reached no matter how dire the situation. That said there were enough discharged veterans around and enough eager teenagers that Rome could easily have assembled 7 or 8 Legions of decent quality very quickly if a threat arose.

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It's the conclusion I've reached too.

That has the problem that the Gauls were mostly unarmored, the biggest problem imaginable because the Gauls got cut up alot more than the Romans in combat.
I should point that wearing armor was hot and annoying; I've worn chainmail in mock battles.

Maybe if you have the Gauls realize as early as you could, the score could change.

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They were still on "every warrior brings his stuff" model: the wealthy had scale armour and a nice sword, the modest farmer had no more than a bronze tipped spear and his everyday clothes. Anyway, I think the biggest problem was more discipline and coordination rather than equipment.

When Caesar entered Italy in 49 BC, he immediately recruited 14 legions (XVII-XXX) for the upcoming Civil War to add to the 12 (V-XVI) he had under arms at that point.

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Immediately? I'm quite sure it's Octavian who raised that many, and in a longer time frame.

Thoresby said:

You're wrong on that. The Romans frequently merged units in order to bring them up to full strength, for example at Philippi we know that of the Liberators two Legions were at full strength and they had just over 80,000 men spread among 17 Legions suggesting an average of 4750 which is not much short of the 5,120 that was a the ToE strength of a Legion at this point.

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60 full strength legions is 307,200 men. Even more if you count auxilaries. By the time of Augusts' death, there were 25 legions, or 125,000 men approximately (not counting auxilaries). Now, I know a lot of legions were disbanded between 42 BCE and 27 BCE when the Roman army size under Augustus was brought to those levels, but I have a hard time believing in the feasibility of disbanding 182,000 soldiers in 15 years. Especially considering the triumvirs had a hell of a time just disbanding them men they disbanded in 42 BCE-hell, that itself almost brought down Octavian itself. Then you have to consider the amount of legions was shrunk in part by Augustus merging many legions together.

jkay said:

The Gauls won and sacked Rome because the Romans had a neocon elected whom worked even worse than our Shrubbies for us.

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Please don't introduce contemporary political flamebait into historical discussion threads.

The Roman Republic was the greatestmilitary power in the Western World by the 3rd Century BC.

Were did all that mobilization potential go in the centuries afterwards?

MrGreyOwl said:

I'm wondering how many Legions Rome could realistically muster to bar Vercingetorix from entering Italy, and/or attempting to retake Narbonnensis Gaul.

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Looking at Caesar's commentaries on the Civil War will give a good indication of how quickly troops can be raised. Pompey has ten legions ready to defend Italy at the start of the Civil War [1.6]. Two of those are pre-war units, but the rest seem to have been newly-raised. On the other side, Caesar raises and completes two legions on the march to Brundusium, not including the twenty cohorts that had defected to him [1.25] which Ahenobarbus had raised from Alba and the Marsi, Pelignians, and neighboring states [1.15]. There's a potential problem in the form of double-counting: Pompey only took five legions from Italy to Greece [3.4], so presumably many of the remaining troops went over to Caesar. However, for a serious emergency it doesn't seem unreasonable that they could raise a force at least equal to Caesar's within a short space of time.

slydessertfox said:

60 full strength legions is 307,200 men. Even more if you count auxilaries. By the time of Augusts' death, there were 25 legions, or 125,000 men approximately (not counting auxilaries). Now, I know a lot of legions were disbanded between 42 BCE and 27 BCE when the Roman army size under Augustus was brought to those levels, but I have a hard time believing in the feasibility of disbanding 182,000 soldiers in 15 years. Especially considering the triumvirs had a hell of a time just disbanding them men they disbanded in 42 BCE-hell, that itself almost brought down Octavian itself. Then you have to consider the amount of legions was shrunk in part by Augustus merging many legions together.

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How on earth is that difficult to imagine? Consider the US Civil War. The Antonian Legions were disbanded in the same way that the Confederates were demobilised, i.e. go home and we'll forget you were on the wrong side, and the Octavian said to his own troops here's a demob bonus* for anyone who want's to leave and and anyone who wants to stay under arms you're heading to the Rhine.


*Paid for by the loot of Egypt.

Dain said:

Were did all that mobilization potential go in the centuries afterwards?

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- the emperors did their very best in order to demilitarize the society for a better inner security.
- the service of a marian legionair was shorter. Rather about 12-16 years than 20-25 years. So there were a lot of veterans in their best age in Italy
- during the empire veterans settled mainly in the provinces and were consequently recruited from there. Italy had not that much veterans anymore.
- the mighty roman landlords opposed succesfully against recruitment of their peasants
- the inhabitants of the more civilized provinces in later centuries were not longer willing to serve in the army; the romans even called them inappropriate and prefered guys from other provinces (Illyricum, Cilicia, ...).

Thoresby said:

*Paid for by the loot of Egypt.

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THIS!

Without the egyptian treasury Augustus would have been in deep trouble.

robcraufurd said:

Looking at Caesar's commentaries on the Civil War will give a good indication of how quickly troops can be raised. Pompey has ten legions ready to defend Italy at the start of the Civil War [1.6]. Two of those are pre-war units, but the rest seem to have been newly-raised. On the other side, Caesar raises and completes two legions on the march to Brundusium, not including the twenty cohorts that had defected to him [1.25] which Ahenobarbus had raised from Alba and the Marsi, Pelignians, and neighboring states [1.15]. There's a potential problem in the form of double-counting: Pompey only took five legions from Italy to Greece [3.4], so presumably many of the remaining troops went over to Caesar. However, for a serious emergency it doesn't seem unreasonable that they could raise a force at least equal to Caesar's within a short space of time.

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On paper, Pompey might have had ten legions, although the fact that he didn't dare meet Caesar's one legion in battle suggests that they weren't actually at battle-ready standard yet. I'd guess either that they were still mostly administrative cadres and hadn't been able to find many recruits yet, or that they hadn't had time to train their men. (Or both, of course.)

Fabius Maximus said:

On paper, Pompey might have had ten legions, although the fact that he didn't dare meet Caesar's one legion in battle suggests that they weren't actually at battle-ready standard yet.

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Actually, the Commentaries strongly suggest that Pompey's inability to meet Caesar in battle wasn't due to his fear or his troops' training. For a start, your point about "one legion" is incorrect. Though Caesar crosses the Rubicon with just the Thirteenth [1.7], he calls his remaining troops from winter quarters [1.8]; he has two legions and eight cohorts shortly after the outbreak of war [1.11], campaigns in Picenium with the Twelfth and Thirteenth [1.15], and when besieging Corfinium has the Eighth, Twelfth, Thirteenth, and twenty-two cohorts of new levies raised from Gaul [1.18]. The latter are presumably those mentioned as being recruited in Ariminium in 1.11, suggesting how quickly the training process was.

Secondly, reading the Commentaries illustrates how Caesar's strategic mobility allows him to swallow up most of Pompey's outlying detachments, scattered across Northern Italy, in the opening moves of the campaign. There's five cohorts at Iguvium [1.12], a garrison at Auximum [1.13], ten cohorts at Asculum and six at Camerinum [1.15], Domitius's twenty cohorts [1.15] and seven cohorts at Sulmo [1.18]. Assuming a minimum of two cohorts at Auximum, that's 50 cohorts or five legions, meaning half of Pompey's original force has vanished before he's even moved his two veteran legions from Apulia [1.14, 1.24]. Note that this estimate of strength fits well with Pompey only having five Italian legions in Greece [3.4] despite summoning all available levies to join him [1.24].

This explains why Pompey decided to leave Italy: not because his troops aren't ready, but because they're inferior in both quality and quantity despite being fully trained. Not only does Caesar's force at Corfinium have numerical parity with Pompey's remaining troops, but it has three veteran legions to Pompey's two and will increase both margins when the Gallic legions arrive. To confirm that the problem wasn't training, Caesar dispatched Domitius's defecting troops to secure Sicily almost immediately after they came over to him- something he wouldn't have done, given that he had veteran troops on hand, if they weren't capable of doing so.[1.25]

MrGreyOwl said:

I'm quite sure it's Octavian who raised that many, and in a longer time frame.

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The original quote is correct: Caesar raised 14 legions in 49, plus an additional seven in 48.