Hadrian's Consolidation - reboot

Ctesiphon, Regnum Parthorum, may 164

Hecatee

Donor
Ctesiphon, Regnum Parthorum, may 164


The battle had been bloody, more than bloody even, murderous. Emperor Marcus Aurelius himself had had to take out his sword and wield it in anger, as had the shahanshah Vologases IV. Now one of them rode his horse on the battlefield, blood spattered on his armor, surrounded by his surviving bodyguard. The other lay at the heart of a mound of dead and wounded warriors that marked the most hotly contested ground of the battle, the spot where the ruler of an empire had fallen.

The Roman army had come south from both the Tigris and Euphrates and joined a few days’s walk above Ctesiphon, concentrating all the might of the Roman Empire : a good fourth of the total imperial forces, some 80 000 men, arrayed for battle against the remaining might of the Parthian empire.

Chosroes had been given overall command of some 150 000 men, with no less than 40 000 horsemen. But numbers were deceptive here as many of the horsemen were young second or third sons without the training and experience of their deceased elders. Loses among the parthian nobility had been horrendous during the previous years with the defeats at Arsamosata and in a number of smaller battles taking the best of the light horsemen and too many of the cataphractoi. The situation was no better with the infantry : the Immortals’ regiment, picked infantry of the empire, had less than a third of its original soldiers surviving the campaign.

Desperate measures had been taken. The wall of Gorgan had been depleted of most of its garrison, despite the threat of the nomadic tribes of the great northern plain : the road toward the heart of the Parthian plateau was open to the barbarians and devastation would follow if the troops brought to Ctesiphon did not succeed in turning away the westerners…

Marcus Aurelius contemplated the death and destruction around him, his face a neutral mask to hide his sentiments, a mix of deep sadness and elation, of worry and pain. So many dead. His cavalry almost annihilated, the praetorian guard gutted with more than half its picked elite force dead, his own commander of the imperial bodyguard, Titus Aelius Borysthene, dead in the thick of the fight that had turned the battle.

Chosroes had convinced Vologases to try a last, desperate operation. Concentrating the last of the heavy cavalry in a single heavy fist, they had charged directly toward the roman imperial entourage, bursting from the center of the parthian lines while the rest of their cavalry kept the Romans and Armenian cavalry to the sides of the battlefield. The heavily armored men then pushed into the roman center, brushing away the infantry under their sheer weight of their armoured Nisean mounts, the largest horses known in the world.

The legionnaires had not been enough to stop the momentum of the charge and the praetorian had been engaged but their desperate defense was not enough and the emperor himself, against the wishes of his high command, had ordered a counter charge. Running in the gap between the back of the legions and the praetorian guard, he’d taken a lead position at the head of his bodyguard, a number of his highest military advisors at his side. The wedge formation had taken the parthian snake of the left flank and penetrated deep in the line where Marcus Aurelius and his bodyguard had fallen on Vologases and his own protectors. The two emperors had exchanged a few blows before being separated by the flow of the battle, but legend would say that it was Marcus Aurelius himself who’d slayed the Parthian King of Kings. It had been Borysthene who’d accomplished the feat, causing the fight to increase in ferocity as the Parthians attempted to bring the corpse of their leader back to their lines. The noblest Parthians fell around the body, many dying not from wounds but from the weight of the bodies that fell upon them, be it horseflesh or men’s.

Yet it was too late. The infantry had reformed and now pushed against the cavalry from all sides, not giving the Parthians the room to take any momentum. The roman imperial entourage went through the Parthian lines and exited on their right flank before going back to their initial position, with Marcus Aurelius’ cloak well in sight to prove to those of his soldiers who looked that he was still alive although he’d received a number of cuts, luckily minor, during the fight. Gallenus tended to them while the emperor was still on horseback looking at the disaster happening in front of him as the roman infantry made contact with the underwhelming parthian infantry who was already beginning to flee as rumors about the death of the Shahanshah began to flow on the battlefield.

While some fled toward the walls of Ctesiphon, most would flee east and try to put the river between them and the romans, who were in no shape to pursue given the losses in cavalry. Beside all wanted to be there for the sack of Ctesiphon…

For Marcus Aurelius the victory was total, too total even : he was not sure whom would try to negotiate peace now, as so many of the Satraps had fallen at the side of their lord. What should the goals of the war be now that so much had been won but that peace seemed unreachable ?
 

Md139115

Banned
If Parthia collapses utterly, that’s going to cause a great deal of butterflies. It might even prevent the rise of the Sassainids. Perhaps the Huns and other step tribes will turn South into Persia and India rather than attacking Eastern Europe?
 
I wonder how much territory the Romans are willing to take on at this point. While it might hypothetically be possible for them to re-establish Trajan's province of Mesopotamia, given the apparent decimation of the Roman armies in the east, that would seem a bit too large to digest. On the other hand, this seems like a perfect opportunity to cement Roman dominance in the near east.
On the other hand, if they try to set up some sort of friendly government, they will have to find some way to weaken it so far as it could not pose too large a threat in the future while at the same time being able to ensure trade with the east and a proper defense against eastern barbarians. It also can't hep that there won't be a whole lot of nobles to negotiate with now that they've essentially slaughtered them all.
Either way, the Romans are really only constrained by what they are willing to take on. I'll be very interested to see where this goes.
 
Good God! That was intense!

With much of the Parthian army and king fallen, we might see an internal crisis occur over succession. With that, Parthia might not fall from Rome, but by civil war.
 

Hecatee

Donor
To clarify the battle and the situation :

- Roman cavalry lost more than half of its force
- Roman infantry is almost intact except for two legions that held the center
- Roman praetorian guard lost half its forces
- Marcus Aurelius suffered minor wounds
- Vologases IV and his top general Chosroes are dead
- 70% of adult (above 15) male Parthian aristocracy is dead, wounded or prisonner
- Rome controls every land west of the Tigris down to Ctesiphon but not yet down to the sea
- Parthian defenses against nomadic tribes is weakened to the point they can't hope to stop a tribe
- Formed Parthian forces still existing are mostly infantry and mostly (beside some garrisons) in modern day Iran. About 60 000 men, mostly levies, are wandering in southern Iraq and western Iran after they fled the battlefield. Most are going home...
- Plague is coming from the East, currently in eastern Iran. Up to 30% death rate in affected areas (OTL Antonine plague)

Now for the future, ideas not yet formalized and which may change later :

- Rome will take everything west of the Tigris, and have a port directly on the arabian gulf around modern day Basra
- Rome will found a number of fortresses on the Tigris, which will become a new permanent border
- Rome controls, via client kingdoms, the Caucasus which is for all purpose and until further notice closed to barbarian raids
- Iran is about to become a mosaic of statelets for at least a few decades until a power manages to unify the region. Said power might not be a local...
- The land Silk road is disrupted due to the instability in Iran
- The plague will not spread out of Iran due to total disruption of trade and the fact the Romans don't let anyone cross the Tigris border
- Nomadic tribes will take new roads south and east. What I'm not sure yet is whether to have early Mughals or to curb them earlier ? Or blunt them at the Indus and leave India east of the river as it was ?
- While further in the future (almost a full century...), the issue of Goths and Huns is already butterflied away : while the Goth will go south they won't have OTL successes due to the Roman border and the Pontic kingdom being stronger. The hunnic pressure on the Goth will also be diminished by the fact that the tribes will have other targets
- China will be an actor in all this because all those troubles will mean more information exchange (as they try to understand why the land silk road has shut down) and thus potential for direct contact with the Romans...
- The closure of the land silk road may develop China's interest in sea trade
 
To clarify the battle and the situation :

- Roman cavalry lost more than half of its force
- Roman infantry is almost intact except for two legions that held the center
- Roman praetorian guard lost half its forces
- Marcus Aurelius suffered minor wounds
- Vologases IV and his top general Chosroes are dead
- 70% of adult (above 15) male Parthian aristocracy is dead, wounded or prisoner
- Rome controls every land west of the Tigris down to Ctesiphon but not yet down to the sea
- Parthian defenses against nomadic tribes is weakened to the point they can't hope to stop a tribe
- Formed Parthian forces still existing are mostly infantry and mostly (besides some garrisons) in modern day Iran. About 60 000 men, mostly levies, are wandering in southern Iraq and western Iran after they fled the battlefield. Most are going home...
- Plague is coming from the East, currently in eastern Iran. Up to 30% death rate in affected areas (OTL Antonine plague)

As for now, I predict that Rome will have to make changes in their current military strategy to rely less on the cavalry. For the Parthians, I predict that nomadic barbarian tribes will flock to Parthia. Not only that but with a majority of the aristocratic elite dead and disillusioned soldiers marching to a grim sick home, there will be absolute chaos and even a potential civil war. The Romans, of course, will be keen to take advantage of the chaos and might find an easier path.
 
I guess that the Persian and Roman situation would be compared to the OTL post Battle of Nehāvand... of course the Roman Emperor isn't planning advanced/expands to the Iranian Plateau however I guess that the Caspian Gates would be fortified/garrisoned.

Also would be supported some kind of puppet king... If could be found somebody that would be adequate and/or willing to do.
 

Hecatee

Donor
I guess that the Persian and Roman situation would be compared to the OTL post Battle of Nehāvand... of course the Roman Emperor isn't planning advanced/expands to the Iranian Plateau however I guess that the Caspian Gates would be fortified/garrisoned.

Also would be supported some kind of puppet king... If could be found somebody that would be adequate and/or willing to do.
Politically yes, although militarily much less so regarding the loss of life : its mainly the aristocracy that paid a catastrophic price because they managed to get their charge deep into the infantry but could not extricate themselves and the infantry did not break completely, the praetorian acting as an anvil on which the Parthian hammer shattered.

About the Caspian Gates, which ones are you thinking about ? (there is confusion between the ones preventing access into the northern Caucasus and the gap south of the Caspian sea). The kingdoms of the Caucasus, roman vassals, are now mostly freed from any fear of the Parthians thanks to the Roman forces while the south of the Caspian sea remains in Parthian hands (for now). In fact the borders of Armenia have not really changed in this war :

If you want to picture the border take the Tigris from the persian gulf up to the Great Zab river (midway between Mossul et Erbil, the first to become a legionary base and the second the main Parthian fortress in the area), follow the river and when it runs dry keep going until the lake Orumieh and then, on the other side of the lake, follow the road 16 to Tabriz (then probably a fortress but not a very important one) and then Ardabil (likely already a city too) and then a straight line to the Caspian : that's the border more or less.

1920px-Arshakuni_Armenia_150-fr.svg.png
 
About the Caspian gates I was referring to those, that at south, controls the access to central Persia and about the possible fortifications I was thinking if would be similar to the Great Wall of Gorgan the defensive forts built (centuries after) by the Sassanians...
 

Hecatee

Donor
About the Caspian gates I was referring to those, that at south, controls the access to central Persia and about the possible fortifications I was thinking if would be similar to the Great Wall of Gorgan the defensive forts built (centuries after) by the Sassanians...
Well it seems that the wall might have existed as early as the Parthians, that's why I mentioned garrisons taken away from there, it will not be in the roman sphere but remains Parthians so no new limes there :)
 
Great TL. I'm hoping the Romans don't expand into Mesopotamia, because barring major political reforms it's going to increase potential political instability in the future. An empire centred around the Mediterranean with easily accessible rivers to inland areas is possible to maintain in the long run. Controlling Mesopotamia which is far from Rome with no easy sea/trade links to foster unity is just a recipe for future ambitious generals to rebel, make a bid for the imperial throne, or set up a separate kingdom. I would expect the division of the Roman Empire to happen much sooner, civil wars to be much more frequent, Rome to become steadily less important as the centre of the empire which would lead to disunity.

Rome is already going to have its hands full with Northern Europe set to undergo an economic and population boom due to agricultural improvements like the heavy plough. Once Gaul and Britannia start to outstrip the Mediterranean economy in many ways, they will be less tolerant of imperial control. Add to that new provinces/territories to the East, and its hard to see the empire staying together in the long run without massive civil and political reforms.

Possible ideas

-Development of a centralized bureaucracy to levy indirect taxes as opposed to direct taxes to diminish general resentment towards Roman political control. Salt and iron taxes taken from the Chinese would help. It could also help reduce corruption by governors and help the empire more efficiently generate revenue if salt and iron officials are separate from the provincial governors/procurators and accountable directly to the emperor.

-To solve the monotheism vs polytheism conflict/problem in the long term and generate revenue: a jizya like tax. Those who refuse to make sacrifices to the emperor can pay an additional tax to demonstrate their loyalty. Not requiring sacrifices to the emperor would weaken political legitimacy as well as make polytheists resent the monotheists even more, furthering religious tensions. A jizya tax would mean those who refuse to make sacrifices are still submissive to Rome, satisfying the polytheists, while not inducing the monotheists to rebel by forcing them to go against their religion.

-To prevent ambitious generals/statesmen from rebelling and participating in civil wars as well as preserving Rome as the political centre of the empire: A legal requirement that all family members of high ranking statesmen/officials reside in Rome as essentially hostages.

-Eliminate all senatorial provinces: due to the nature of elections/bribery, senatorial provinces are often plundered to pay back debts taken by statesmen to win them elections.

-Cement the Senate as being the sole legal road to hold high military office. Make equestrians hold solely administrative positions. The reason for this is that it originally was the disconnect between the military establishment and the elite Senate/wealthy members of Roman society that led to the loss of legitimacy for the Roman state as well as civil instability. Once you create a military class with no allegiance to Rome's political interests and long term well-being, once you allow political outsiders to bid for the imperial purple just from military rank alone, you destroy the foundations of the political system as those outsiders seek to favour the military and undermine the system in order to stay in power. The OTL transition from Senators holding high political and military office to the equestrians being favoured by the emperors and their replacement of senators led to chaos and civil wars as Rome's political class lost legitimacy in the eyes of elites, soldiers, and provincial subjects.

-State bonds to avoid the currency debasements that lead to a massive breakdown in trade.

-A progressive land tax? A wealth tax on the value of all land holdings exceeding a current amount would lead Rome's wealthiest class to invest their capital into investments that would be more productive for the economy in the long run rather than buying up yet more land if they are penalized for holding too much land.
 
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Rome is already going to have its hands full with Northern Europe set to undergo an economic and population boom due to agricultural improvements like the heavy plough. Once Gaul and Britannia start to outstrip the Mediterranean economy in many ways, they will be less tolerant of imperial control. Add to that new provinces/territories to the East, and its hard to see the empire staying together in the long run without massive civil and political reforms.
I've heard this being said before but it makes no sense. Assuming just combined population the modern western Mediterranean states i.e. the North African ones, Italy, Spain and Portugal you have the economic advantage leaning towards them. Using modern GDPs which are the result of how our world went the western states plus the modern states of Illyrian at the very least equal France and Britain. Throw in the rest of the Mediterranean, the fact that I didn't count southern Gaul and all the changes of such a timeline I don't see how Britannia and Gaul will outstrip the entire Mediterranean economy.
 
I've heard this being said before but it makes no sense. Assuming just combined population the modern western Mediterranean states i.e. the North African ones, Italy, Spain and Portugal you have the economic advantage leaning towards them. Using modern GDPs which are the result of how our world went the western states plus the modern states of Illyrian at the very least equal France and Britain. Throw in the rest of the Mediterranean, the fact that I didn't count southern Gaul and all the changes of such a timeline I don't see how Britannia and Gaul will outstrip the entire Mediterranean economy.

Well OTL, the dominance of Northern Europe over Southern Europe/Mediterranean is well attested. It began with agricultural improvements like heavy plough, three field system, and horse collar/horseshoes. Suddenly it was Northern Europe, including Germany-France that was the centre of Europe's political gravity. Previously it had been the Mediterranean world dominating Northern Europe.

The heavy plough/three field rotation doesn't help the clay soils of the Mediterranean world (that don't see much summer rains) that much. If Gaul achieves twice the population of Italy for example, that's going to lead to control/legitimacy problems, as to how Rome can justify continued imperial control and being the political centre of gravity with Gaul being right next door possessing so many more people. OTL, France and Germany dominated Italy starting from the Middle Ages.
 
Another minor quibble. I'm not an expert on Parthia, but I feel there's no way the Parthians could have mustered 150,000 men in the defence of their capital. OTL the Parthians only mustered armies in the vicinity of 60,000 men against the Romans. Maybe 80,000 is possible, but 150,000 seems over the top. Their level of military organization just didn't match the Romans' centralized professional army size, they relied on feudal levies and powerful nobles would always withhold a certain portion of available men.
 
Well OTL, the dominance of Northern Europe over Southern Europe/Mediterranean is well attested. It began with agricultural improvements like the heavy plough, three field system, and horse collar/horseshoes. Suddenly it was Northern Europe, including Germany-France that was the centre of Europe's political gravity. Previously it had been the Mediterranean world dominating Northern Europe.

The heavy plough/three field rotation doesn't help the clay soils of the Mediterranean world (that don't see much summer rains) that much. If Gaul achieves twice the population of Italy for example, that's going to lead to control/legitimacy problems, as to how Rome can justify continued imperial control and being the political centre of gravity with Gaul being right next door possessing so many more people. OTL, France and Germany dominated Italy starting from the Middle Ages.
Yes, but this was OTL France and Germany. Not a France which is part of the same polity as Italy or a Germany who despite its population still has a much larger neighbour. OTL, where France had been unified for much longer, had France at 16 million in 1500 AD which, while larger than, Italy's 11 million wasn't double with Italy's internal warring and population depletions to be considered and the effects any POD could have. Even if France does outstrip Italy it won't outstrip the entire Mediterranian especially considering that during the Principate when this timeline is set Gaul was divided into 3 or 4 provinces (depending on if Belgica is Gallic) compared to Italy's one.
 
Yes, but this was OTL France and Germany. Not a France which is part of the same polity as Italy or a Germany who despite its population still has a much larger neighbour. OTL, where France had been unified for much longer, had France at 16 million in 1500 AD which, while larger than, Italy's 11 million wasn't double with Italy's internal warring and population depletions to be considered and the effects any POD could have. Even if France does outstrip Italy it won't outstrip the entire Mediterranian especially considering that during the Principate when this timeline is set Gaul was divided into 3 or 4 provinces (depending on if Belgica is Gallic) compared to Italy's one.

Yes but I believe the author hinted Rome was going to subjugate Germany by the end of the second century. What I'm trying to say is that within the empire, Gaul and Germania are going to exert huge influence that will compete for Italy's attention with the Mediterranean provinces + eastern provinces. This tension will be difficult to reconcile.

As for populations, there were times when France was nearly double that of Italy. It certainly has double the agricultural potential at least. But even if that doesn't happen, you have to admit the Mediterranean economy is going to be less important overall to the empire in the future compared to the internal economies of Gaul, Germania, Britannia, even Hispania and Dacia. Historically the Mediterranean economy was the thing that undergirded the unity of the Roman Empire. It's going to be more challenging to maintain that unity when the provinces develop more inner trade that doesn't rely on the Mediterranean as a conduit.
 
I wonder how much territory the Romans are willing to take on at this point. While it might hypothetically be possible for them to re-establish Trajan's province of Mesopotamia, given the apparent decimation of the Roman armies in the east, that would seem a bit too large to digest. On the other hand, this seems like a perfect opportunity to cement Roman dominance in the near east.
On the other hand, if they try to set up some sort of friendly government, they will have to find some way to weaken it so far as it could not pose too large a threat in the future while at the same time being able to ensure trade with the east and a proper defense against eastern barbarians. It also can't hep that there won't be a whole lot of nobles to negotiate with now that they've essentially slaughtered them all.
Either way, the Romans are really only constrained by what they are willing to take on. I'll be very interested to see where this goes.

Take enough territory to constitute a natural "defensible" border. Beyond that, establish puppet/vassal governments who pay tribute to Rome. Unless you have vast hordes of poor/unlanded/barbarians that you can resettle in these eastern provinces...vassal governments are a better bet.
 
Yes but I believe the author hinted Rome was going to subjugate Germany by the end of the second century. What I'm trying to say is that within the empire, Gaul and Germania are going to exert huge influence that will compete for Italy's attention with the Mediterranean provinces + eastern provinces. This tension will be difficult to reconcile.

As for populations, there were times when France was nearly double that of Italy. It certainly has double the agricultural potential at least. But even if that doesn't happen, you have to admit the Mediterranean economy is going to be less important overall to the empire in the future compared to the internal economies of Gaul, Germania, Britannia, even Hispania and Dacia. Historically the Mediterranean economy was the thing that undergirded the unity of the Roman Empire. It's going to be more challenging to maintain that unity when the provinces develop more inner trade that doesn't rely on the Mediterranean as a conduit.
I think the disconnect is what you mean when you say Mediterranean. You seem to be talking about mainly Italia in relation the other provinces and so yes the individual provinces may and probably will eclipse it in population. I'm talking about all the Mediterranean provinces from the Pillars of Hercules to Red sea which due to its scope and size will almost always be a massive population and economic centre for Rome. Just Italia on its own or mainly Italia is a different thing altogether.

Even if the Mediterranean isn't the only conduit it will most likely be the greatest one due to the size of all provinces on it and all the trade that will be going through it from the East and even the trans-Sahara. Gaul will also be connected through its south which was quite closely linked to Italia during the empire. Northern Gaul, Britannia and Germania will be population centres but their size depends on the events that occur and I admit that the heavy plough would revolutionise the Northern European states, in such an Empire all the province are likely to benefit from such, that's why Egypt and North Africa despite being high food exporters and must have provinces didn't immediately shift political power towards them.
 

Hecatee

Donor
Great TL.

Thanks ! I'm trying to keep it great so that no one needs to make it great again later on :p Thanks too for the great comments, to which I'll now try to reply in one structured message which I'll put in "spoiler" mode so that those who want to read the story without reading my take on things before time may do so.

First on the question of the size of the Empire and the future of the new conquests. It is indeed true that the empire is becoming too big and that communication (or the difficulties of communication) with some parts make it easier to revolt, especially in the East. Yet Rome will not let go of these conquests for two reasons :

1) It is the trajanic project that is being realized here, and the original trajanic plan did not support vassal states : even Armenia was turned into a province in 116 before becoming a roman vassal kingdom again under a cadet branch of the Parthian ruling family, which is still in place with its king newly reinstated in power by Marcus Aurelius.
2) Romans have a new access to the maritime trade of the east/southeast which is not as dependent on the trade wind patterns as the Egyptian-based trade. This has two effects : Egypt is less of a vulnerability (especially the always volatile Alexandria) to Rome and taxes will actually increase slightly due to the inter-provincial trade tax, which will now have to be paid more often than before (before : foreign trade tax when landing in Egypt and interprovincial trade tax when landing in Italy. Now : foreign trade tax when coming in Basra, one or two interprovincial taxes before it arrives on the Mediterranean, and once more when arriving in Italy)

Now the military threat from revolts is also diminished because the eastern legions will be more distant from each other than before and thus under more governors : no "uber governor" able to mass an army to overthrow the empire, and the distances also mean that now there is enough time to try to solve the issue of usurpator by other means, mainly assassination. While I still have to make a map of the new legions' distribution, a number of legions will be based on the new border, some will remain in Cappadocia and some will remain in Syria itself due to the Jewish problem, even if it has been largely settled in the Roman empire (and I've may not have stressed things enough in the last few posts but the Jews who fled into Mesopotamia have been savaged by the recent war, some fled further East but they are really a small people by now...)

Which leads me to the religious question. Which is simple : monotheism, in this world, is really really minor in comparison with OTL. First the Jews and Christians have had more major losses earlier than OTL, and the Jews have been mostly uprooted and sent to the wind much wider than OTL. Second, Manicheism has been dealt a huge blow by this war, something I've not touched upon until now : it seems to have been around this time that manicheism's central texts have been gathered by the imperial Parthian regime, which just broke down... So less organization, less centralization, less structure than OTL (one forgets how much an organized religion manicheism was). All this also mean the the idea of a tax on the "wrong" believers is not going to happen as it is almost a non issue and not honoring the emperor in the proper way is simply a capital offence.

About institutions. The move toward more role of the equestrian order in the civilian and military running of the empire was a huge trend already in the time of Hadrian, and I see no driver for change here. To the countrary the new institution of the Academia Militaria Practica and appended functions only go further in this direction. Don't forget that often centurions not promoted from the rank and file were of equestrian rank and many of those that were not at the beginning of their military career achieved this rank at the time of their retirement. The military also played an important role in the running of the provinces, for instance running a number of the toll that collected the trade taxes.

This being said, I see a gradual reinforcement of the administration and its professionalization, and this will play without the senatorial order. Those will be the richest men of the Empire and there power will essentially come from their access to the emperor, their judiciary role and their wealth. They will keep a cursus honorum that will culminate with provincial governorship, but I see an inflexion toward the judiciary and infrastructure building while the financial aspects of the job will go to equestrian in a parallel cursus. Corruption will thus evolve toward new actors and forms.

Note also that by this time elections are a joke and all the candidates are appointed by the Emperor, so this is no longer an issue.

About economy and taxation, you've suggested good ideas I might follow upon but I'm not in agreement with you for what regards demography. Rome was very efficient in bringing local elites into the roman political game, and so the senators from Gauls see themselves as Roman senators firsts, from Gaul second. Rome is undisputed center of the Empire for ideological and historical reasons and no one will change that. What an increase in population may bring on the other hand is an increase in revenue, transforming some deficit provinces into bonus provinces. It will lead to improvement in security and better infrastructures which will in fact increase the local attachment to Rome.

About the Parthian army : it is a maximum effort in a defensive situation with a mass levee of the every available men, including garrisons from lands the Romans have never seen or heard from, amalgamated into a huge (and unwieldy) mass intended to swallow the Romans and hold them in place for long enough so that the cavalry may break then. Yet this time the Romans have cavalry, a lot of it, and are able to neutralize the main Parthian shot (pun intended), leading to the fateful charge that destroyed Parthia's elite.
Note that even Rome's army (100 000 in theater, 80 000 on the battlefield) is immense and larger than any roman army used except those of Trajan, even Julian II's army only had a 60 000 strength.
 
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