Would giving far eastern Anatolia to the southern half Deal with thatThe Northern Empire gets super fucked here. It has to fight all barbarians everywhere and still has to worry about Persia as well.
I was thinking something along the lines of one empire against Germans and one against PersiansIt is hard to find a reason at all, why the romans should divide the empire in a northern and a southern part. The later division was already done between Octavian and Antonius by good reasons.
I prefer alternate histories with a rock-solid WHY and HOW, before asking what then could happen.
I was thinking something along the lines of one empire against Germans and one against Persians

Oh, that is a good map.This would be better IMO:
View attachment 256796
It's somewhat similar to the de-facto split during the Crisis of the Third Century.
Emperor #1 sits in Antioch. His job is to battle the Persians. He is the richest of the 3, with his main source of income being the large cities along the coast of the eastern Mediterranean and his export of Egyptian grain. He needs the money though, as holding the Euphrates is by far the most expensive Roman project. Secondary concerns are keeping the various princes in the Caucasus vassal to Rome and also making sure the Arabs keep quiet.
Emperor #2 sits in Naissus, which is nicely situated around the half-way point between the Black Sea and the Rhine, and also a bit into the interior. His job is to prevent anyone from crossing the Danube. The Senate in Rome is nice enough to manage Italy for him, as well as the grain supply in Carthage. Taxes from the cities around the Aegean are another major source of income for him, whilst Illyria and Thrace provide most of the manpower.
Emperor #3 sits in Augusta Treverorum, close both to Gaul, the Rhine and Britain. His job is to keep the Rhine secure. As demonstrated by Julian, the Romans can get a lot done if there's an emperor actively managing this sector. Secondary objective is keeping Britain safe. Gaul and Spain provide most of his income
EDIT: Raetia and Cisalpine Gaul can switch between Emperors #2 and #3 depending on the circumstances
Oh, that is a good map.
But my vision of the division of the Roman Empire is somewhat different.
I truly believe that you do not take my disagreement personally
I am sorry I cannot make a map now.
The Roman Empires:
#1 - the Balkano-Anatolian Roman Empire.
As the tin says - the Balkans + Anatolia. Similar to the Medieval Byzantine Empire which proves that this entity has natural borders and is very defensible. The main concerns are the Barbarians across the Danube and Persia. Armenia and some Caucasian entities are possible vassals if they are not vassalized by Persia at the moment.
#2 - the Egyptian-Syrian-Tripolitanian Roman Empire.
That is very defensible as well. The core is Egypt of course. Egypt defending itself against all the invasions has a truly remarkable history. The Mamlyuks holding against the Ilkhan Hulaguid Mongol Iran is my favorite example.
I gave Tripoli to this Roman Empire as a an important source of the Berber cavalry and additional finances.
* Roman Empires #1 and #2 are natural allies against Persia as they know that if one of the Roman Empires falls to the Persians, the other Roman Empire will be the next victim. But every Empire is able to hold against the Persians independently by itself probably loosing Anatolia or Syria to Persia for some time in the process.
#3 - the Italo-Illyrian-African Roman Empire
(the "African" here means coastal territories of the modern Tunisia and Algeria)
Of course the main concern of this Empire is the Northern European border.
#4 the Gallo-Iberia-African Roman Empire
(the "African" here means the coastal territory of the modern Morocco mostly)
The Rhine border is the obvious most important frontier.
#5 the British Roman Empire
that's simple. The smallest Roman Empire. Something like we had in OTL - the Britannic Roman Empire
the main concern is to survive, but having good navy and coastal fortifications it's possible
Your "Gaullic" Roman Empire does not have recourses to pay the legions holding the Rhine border against the Germanic peoples.Note that, for this purpose, i gave all of Western Africa to the Central Empire, because this way it can "blackmail" the Western empires into giving assistance on the Danube if an Attila emerges.
The idea of a monarch ruling one territory, after that him ruling another territory and after that he goes to one more territory is a good one.Essentially, everything rotates around the Central empire, even the minor imperial offices. There would be an order, or cursus honorum, to pursue before becoming Central emperor. Think of it as a more complex tetrarchy.
Hm, long term all the empires are going to be competitors, rivals, allies whatever. There will be even wars between them. It is not the perfect world we are living in.I agree mostly, but keep in mind that empire 1 and 2 are going to be rivals in the future.
I agree mostly, but keep in mind that empire 1 and 2 are going to be rivals in the future. Just like the ERE saw the WRE as a rival in the late IV century.
Not really rivals, but i suggest you to take a look at Stilicho's life. Court rivalry often weakened the state.
As you can see in the map, the division i suggest is to have the division to leave most of the power to the Central Empire, thus making eventual secession/rebellions less probable.
Also, by having a strong Central Empire you can expect it to extend its prerogatives over the other empires is times of relative peace, a thing that would allow empire-wide reforms and thus keeping the roman culture togheter.
Note that, for this purpose, i gave all of Western Africa to the Central Empire, because this way it can "blackmail" the Western empires into giving assistance on the Danube if an Attila emerges.
The Eastern Empire instead will have the resources to fend off the Persians without having to watch barbarians on the Danube. Also, it wouldn't have the resources to seize the Central imperial office, because of the Persians in the backyard.
Essentially, everything rotates around the Central empire, even the minor imperial offices. There would be an order, or cursus honorum, to pursue before becoming Central emperor. Think of it as a more complex tetrarchy.
I have another idea for a three-way split:
A Western Empire and Eastern Empire mostly like OTL, *except* for Egypt and the rest of Africa which form a Southern Empire.
The Southern Empire would probably be the richest of the three, but it would also be given the entire responsibility for keeping the Mediterranean safe from piracy - only fair, since the so much of its riches derive from grain exports out of Carthage and Egypt which go north to Europe.