WI Large scale civil war in the 3rd century CE

In various posts, it´s become clear that, during the Crisis of the Third Century, there were many rebellions and uprisings. Many of them occurred within the Roman Army and took the form of elevating usurper emperors, which never changed anything in the long run (and probably also wasn`t meant to).
Others didn`t, and they were bent on some sort of change (although of different kinds): the Agonistic Christians in North Africa, the Bucoli in Egypt, various "latronicia" in Italia, the Bagaudae in Gallia. Religious persecution, declining living standards and structural socioeconomic changes especially in the countryside (sliding towards the unfree colonate) were common roots, and, unsurprisingly, some items recurred on the agendas of the various rebel groups, e.g. land redistribution, debt cancellation, and the chance to follow their own religious rules undisturbed.
Being isolated from each other by space and time, lacking capable leadership and/or an overarching coherent framework, none of them achieved anything; the weakened Empire, although simultaneously faced with various external threats, too, still managed to hold them all down. Only a few decades later, religious freedom would be decreed from above, and another century later, the landholding Roman aristocracy lost most of their properties to invading Germanic tribes anyway - but those who had rebelled in the 3rd and 4th centuries (and before and after) would not benefit from that.

I am somewhat stuck with my timeline ("Res Novae Romanae"), that`s why I come to you with this question:
Let´s assume that several of the above groups, and more, rise more or less simultaneously, and that a part of the educated elite (both civic/urban and military) plays their vanguard, with one or two leading guys formulating a reform/revolution agenda with broad appeal to the OTL politically apathetic plebs (let´s think of Kleisthenes of Athens or the Gracchi as a historical antecedent/model).
- How far could a conspiratory network/confederacy/alliance realistically stretch, in terms of geography?
- Which places would be most likely to be rebel strongholds, which places would be least likely?
- How strong would a rebel alliance have to be to tip the balance of power in their favour and prevent a reconquest by the old establishment?
- If the rebellion / revolution is not put down, how long does it take to gain complete control over a cohesive territory?
- If the old elites manage to hold onto power somewhere, how will they adapt to the changed situation?
 
...and if the revolution fails: What are the consequences for Roman imperial policies in the following decades? Is Constantine`s embrace of mainstream Christianity butterflied away?
 
A very good question, and I will give my best efforts to give a good answer.

Well during the crisis of the third century, people tended to be more local focus, that being one of the reasons why the legions would revolt, so a revolt of that kind would be in a single geographic area (ex: Gaul, Hispania, Italia, etc... you get the drill).

The most likely places to rebel would be the ones under foreign attacks. If the Empire is attacked at the Rhine and the Persian frontiers, the Emperor would be only able to be in one of the conflicts, making the troops in the other border felling abandoned and then, if they achieve a military victory, they would elevate their general to the purple, because in their eyes he would be more interested in protecting their lands than the original Emperor. Places were peace was common would have less reasons to revolt, given that then the Emperor would attack them.

About the elites, at this time the effective control of the army was in the hands of the professional equestrian elites, especially the ones from illyria, so you don't need the elites for a successful revolt, but you desperately need the army officers, and they defended the status quo.

About your third question, it all comes down to what area revolts, but no matter how strong they are, eventually they would break into several factions, for supreme control. In the end, even if they manage to keep together, the army might have other ideas about, who should rule.

In your fourth point, you ask how long it would that for them to achieve control over an area, and given that the provinces already had the infrastructures I think that it would be very fast. For most people it would only be a change in the governor, and the rest would be the same.

The old elites, would pretend to support the new leadership, but if their power/wealth is threaten then they would plot to bring the regime down. Their actions would go from selling secrets to the enemies, to bribe the legions to bring them down, etc...

If the revolution fails it would be business as usual. The Emperor would be more interested in fighting the next enemy or killing the next usurper, than to be interested in the reasons for the revolt. And the people from the other side of the empire would be more preoccupied with their own problems.

For most the Empire gave them relative peace and stability, and the ones more interested in revolt would be the ones that wanted power or wanted to put their relative group in power.
 
Thanks for your comprehensive reply, Karolus!
I acknowledge the key position of army commanders, and in the case of military revolts, they obviously occurred along threatened borders (which was where most troops were stationed in the first place).
But there were also social and religious rebellions which often occurred in comparatively safe locations: the Bucoli rose in Egypt, which, except for the very South, wasn`t threatened by anyone; the Gallic Bagaudae had their strongholds in inland Armoricum and Aquitaine, where marauding Franks in the 3rd century seldom reached, neither overland, nor by sea. The latronicium of Bulla Felix was in the Latin Italian heartland. The Agonistici roamed in Africa, where there were a few Berber incursions, but otherwise things were quiet.
What do you all think about the peasant population as a political-military factor? They must begin as untrained and unarmed hordes - on the other hand, they are the vast majority of the population and, in a defensive position, they can sustain themselves. In Classical and Medieval China, peasant rebellions brought down many dynasties and established new ones, why not in some parts of the Roman Empire?
Also, what about gladiators on the rebel side? (I know I`m thinking too much about Spartacus...)
 
What do you all think about the peasant population as a political-military factor? They must begin as untrained and unarmed hordes - on the other hand, they are the vast majority of the population and, in a defensive position, they can sustain themselves. In Classical and Medieval China, peasant rebellions brought down many dynasties and established new ones, why not in some parts of the Roman Empire?
Also, what about gladiators on the rebel side? (I know I`m thinking too much about Spartacus...)

Given that at this time politics were interlinked with the military, the peasants had to have weapons, and that is a problem because:

The Roman Law position on the ownership of weapons contradicts itself and is very hard to understand, so some of the sources i see claim that the ownership of weapons was illegal, expect if your job demand you should have means of protections. And while the Codex Justinianus is very supportive of an individual’s right to self defense, it's position on the treatment of the private possession of weapons is mixed.

So lets admit that the peasants can own weapons, they will be unable to produce enough of them to face the legions. Even in a defensive position, the Legions were experts in capturing fortified positions, so the rebels had to find an amazing defensive place and it wouldn't hurt for them to have a 10-1 advantage.

Now the second problem. The peasants didn't really cared about who ruled the Empire, as long as they keep peace in their area. The peasants wanted protections, most of the times, not revolt. Don't forget that in the 3rd century revolt, instability and war were common in the Empire, and the peasants wanted peace, not war, and they didn't cared who gave it to them.

About the gladiators, you probably chose the worst time for them. The third century was a time were Emperors lacked money to gladiator games, and so they were in Decline. Actually I bet most gladiators were conscripted into the army.

Most of the revolts that happened were either unhappy peasants, bandits or religious extremists. And like i said most people didn't cared of who ruled, or what was his religion or politics, they had enough problems with trying to feed themselves and paying the taxes, they only wanted peace and stability and revolt would bring non of that.

But if you need a revolt for your TL, my suggestion would go to the groups that never became an integral part of the Empire, Jews and religious extremists.

P.S. If you want to see more on roman weapon ownership, that may come in handy to explain how they got their original weapons, https://www.saf.org/journal/16/TheR...ePossessionofWeaponsintheCodexJustinianus.htm
 
Once again, thanks a lot, Karolus; a lot of food for thought.

One (hopefully last) question:
If one or two legions joined / supported a revolt, and they`d find that they needed a lot more manpower (and perhaps ships for their navy, too) to hold out against the (rest of the) Empire: How fast could ordinary peasants / serfs be trained to become functioning soldiers in land forces or on warships respectively?
 
One (hopefully last) question:
If one or two legions joined / supported a revolt, and they`d find that they needed a lot more manpower (and perhaps ships for their navy, too) to hold out against the (rest of the) Empire: How fast could ordinary peasants / serfs be trained to become functioning soldiers in land forces or on warships respectively?

It was during the crisis of the third century that the military equipment of the legions begun to change from the gladius and the scutum to the spatha and the oval shield. The reason of that change was because it was easier to use the new equipment, the recruits had to go trow lower training times so you could have reinforcements readier in time.

So if two legions, lets say in Britannia, revolt and manage to get support from the plebes, as long as they have money and equipment they would be able to prepare a big number of soldiers.

About the warships, the equipment and training would be identical, for romans the navy was just another arm of the army like the cavalry, so they could train large number of men very easily, the problem would be to get enough trained sailors to man the ships.

So given the circumstances you gave, I think that in Britannia if the rebels keep a strong navy, and they can, they would have enough time to train a large number of soldiers. With old style equipment to have a battle ready cohort you would need one to two months, to ensure that they get used to the gladius and the way to use it, but with new equipment (spatha, oval shield) at the worst it would take one month to have a battle ready cohort, given that at this time their training would be more focus on teaching them to keep discipline, than into teaching them the how to use their weapons.
 
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