Gaul Rising

This is an alternate timeline in which the Gallic Empire, which in our timeline was a short-lived breakaway state from the Roman Empire, manages to hold on to its independence.

Author's note: I would appreciate any suggestions you have. You can either post suggestions on the article's discussion page or my own talk page. I am also okay with you making minor edits, such as spelling or grammar corrections; but I would prefer that nobody other than me make major additions or revisions. Thank you and enjoy this timeline.

 Pacificus   Viridis 

The Crisis of the Third Century
For much of the Third Century, the Roman Empire was in a constant state of civil war.

It began in 235 AD, when Emperor Alexander Severus was murdered by his own troops, who felt he was not being aggressive enough in dealing with a Germanic invasion of Gaul. Alexander Severus' forces declared Maximinus Thrax the new Emperor. Thrax was not popular in the Roman Senate, so when Gordian, the governor of the province of Africa Proconsularis, rebelled in 238, the Senate proclaimed him and his son Co-Emperors. The rebellion failed, but the Senate appointed another pair of Co-Emperors as Thrax was preparing to march on Rome to punish the Senate. The Senate's choices were unpopular among the masses, so the masses declared Gordian's grandson Emperor. This led to anarchy in the city. Meanwhile, Thrax's invasion of the city failed, so his troops killed him out of dissatisfaction.

The downfall of Alexander Severus, the reign of Maximinus Thrax, and the rebellion of Gordian I and Gordian II were the start of a vicious cycle in which a general or provincial governor would rebel against the current Emperor, possibly gain the acceptance of the Senate, immediately have to deal with an external invasion or rebellion, and in many cases be killed by his own troops, who would then align themselves with a new contender for the throne. Generals turned their attention more toward fighting each other than protecting the Empire's external borders, which led to frequent invasions by barbarian tribes. Another problem that resulted from the constant civil war was severe inflation: each time someone would declare himself Emperor, he would promptly have a large supply of coins with his face on them minted to pay his troops. This state of affairs lasted for decades.

The Rise of Postumus
Marcus Cassianius Latinius Postumus was appointed governor of the Roman border province of Germania Inferior by Emperor Valerian during the 250s. Valerian ruled from 253 to 260 alongside his son, Gallienus. After Valerian died, Gallienus reigned alone. In 258, Gallienus appointed his son, Saloninus, a subordinate emperor.

In 260, Valerian was waging a campaign against Persia (which resulted in his capture and execution by the Persians) and Gallienus and his forces went to Pannonia to deal with a rebellious general. Postumus, Saloninus and Saloninus' mentor, Silvanus, were tasked with defending the Rhine frontier. They were stationed at Colonia Agrippina (Cologne).

Now on October 25, 260, Postumus and his forces intercepted an army of Juthungi (a Germanic tribe) that was returning home from a battle at Mediolanum (Milan). The Juthingi had lost the battle but nevertheless managed to carry off captives and other booty. Postumus's army defeated the invaders and then divided their loot among themselves. Saloninus, at the recommendation of Silvanus, ordered Postumus to hand over the loot to him. Postumus and his troops refused, and Postumus' troops declared him Emperor on November 2. Postumus and his army then laid siege to Colonia Agrippina. On December 9, Saloninus and Silvanus surrendered and allowed Postumus and his forces into the city, and were thereafter executed. Ever since then, December 9, 260 has traditionally been considered the date that Postumus' reign officially began.

Postumus was immediately recognized as Emperor in the Gallic provinces (except for Gallia Narbonensis), Germania Inferior, Germania Superior, and the Alpine province of Raetia. Within a year, the Britannian and Spanish provinces also aligned themselves with Postumus; and Gallia Narbonensis followed a year later. Postumus made Colonia Agrippina the capital of his realm and set up a system of government similar to that of Rome as it was before the death of Alexander Severus. The coins minted under his authority were of an unusually good quality for coins for those days. Rather than seeking control of the rest of the Roman Empire, Postumus focused on defending and bringing stability to the provinces he ruled; and he was indisputably successful at achieving this goal.

Gallienus had to leave Postumus alone for several years, as Germanic tribes were constantly invading the areas still under his control. He challenged Postumus for the first time in 265, sending Aureolus, a general loyal to him, to invade the breakaway provinces. The campaign failed as a result of carelessness on the part of Aureolus. Two years later, Gallienus himself invaded Postumus' realm, but this invasion also failed. Gallienus did manage to retake Raetia in the latter half of 266.

Point of Divergence
The point of divergence between this timeline and ours occurs in 268. Aureolus, who was at that time stationed in Mediolanum (Milan), openly defected to Postumus. Gallienus promptly led an invasion of Mediolanum.

What Happened in OTL
Postumus chose not to come to Aureolus' aid. Gallienus' forces laid siege to Mediolanum. During this time, Gallienus' senior officers murdered him and proclaimed Marcus Aurelius Valerius Claudius (Claudius Gothicus) Emperor. Aureolus surrendered to Claudius II, only to be executed thereafter.

Postumus' decision not to help Aureolus marked the beginning of the end of his rule. His armies became discontented with him, which is evidenced by a sudden decline in the quality of the coins issued under his authority in 268: he had more coins produced in an effort to buy the loyalty of his troops. One of his generals, Laelianus, declared himself Emperor. Laelinus was stationed in Moguntiacum (Mainz), so Postumus led forces that were still loyal to him to invade Moguntiacum. Postumus defeated Laelinus, but then forbade his soldiers to plunder the city. For this, they murdered him and proclaimed Marcus Aurelius Marius the new Emperor.

Thereafter, the territory Postumus had controlled fell into the same state of disorder that the Roman Empire as a whole had fallen into more than thirty years before. Postumus' realm became increasingly weak; and in 274, Roman Emperor Aurelian reconquered what was left of it.

What Happened in This Timeline
Postumus decided to lead a campaign to Mediolanum to help Aureolus out. The combined forces of Postumus and Aureolus managed to repel Gallienus' campaign. Gallienus' senior commanders, who wanted him dead anyway, murdered him and proclaimed Marcus Aurelius Valerius Claudius the new Roman Emperor.

The Remainder of the Reign of Postumus
Postumus' victory at Mediolanum was an important one. The direct result of the victory was that he now had an ally in Aureolus and control of Mediolanum and the surrounding area. Postumus never intended to invade Rome; but he did anticipate that doing so could be necessary as a defensive action, and Mediolanum would be an important point from which to launch such an invasion should he deem it necessary. Also, Postumus would now be able to invade Raetia on two fronts, one being from the west and the other being from the south. The area also served as a buffer between Roman territory and Postumus' core territory.

Claudius II, the new Roman Emperor, had to immediately turn his attention to the Balkans and the Aegean Sea, where various Germanic tribes were carrying out a massive naval invasion. Claudius II was able to drive out the invaders after the Battle of Nassius. This was an important victory for the Roman Empire as it neutralized the threat of the Germanic tribes north of the Danube for more than a decade. After the victory, Claudius II took the title "Gothicus".

Shortly thereafter, an army of Alammani and Juthingi invaded Raetia. Armies loyal to Postumus came to the aid of the forces stationed in Raetia before Claudius II could arrive, and the combined forces successfully repelled the invasion. The governor of Raetia, in gratitude, aligned himself with Postumus.

Claudius II began planning to invade Postumus' realm, but he was forced to put his plans on hold in order to travel to Pannonia to deal with Vandal raids. Before he could engage the Vandals, however, he died of smallpox in January 270. He was succeeded by his brother, Quintillus, who in turn died and was succeeded by Aurelian by September 270.

Early Administrative and Constitutional Reforms
In 271, Postumus established a clear procedure for imperial succession. This was an important constitutional reform, because one of the original causes of the political instability in the Roman Empire was a lack of such a formally defined procedure, so the establishment of a formal process offered the promise that Postumus’ empire could remain internally stable long after his death. It was also significant because it gave the Senate some say in the process of imperial succession. The guidelines he established were as follows: the Emperor could designate a person to succeed him upon his death or abdication; and if the Emperor were to die or abdicate without a designated heir, the Senate would have the exclusive power to elect a new Emperor. In 274, he also gave the Senate the power to depose the current Emperor, provided that the Senate first come to an agreement upon who the new Emperor should be. The purpose of this second edict was to discourage armed rebellions against unpopular Emperors.

Postumus also began reorganizing the provinces under his rule during this time. At first, the changes he made were rather modest. In 271, he divided the province of Lugdenensis into smaller provinces. Then in 273, he formed two new provinces from parts of Aquitania. More significant reforms, including changes to the actual administrative structure of the provinces, would come later.

The Gallic War for Independence
Main article: Gallic War for Independence

Prelude
At the time that Aurelian became Roman Emperor, Postumus was still in a very good position. From his capital in Colonia Agrippina, he ruled over Gaul, Spain, Britannia, Raetia, and the majority of the northwestern Italian region of Transpadana (this was the area that surrounded Mediolanum). He had successfully defended his domain from external invasions. While the main empire was still tormented by civil war and external invasions, Postumus' empire was enjoying a state of stability and prosperity unknown since the death of Alexander Severus. Postumus' popularity had grown, especially after his battle against Gallienus at Mediolanum and the campaign against the Germanic invaders of Raetia that led to Raetia voluntarily rejoining his empire.

Yet Postumus' success was partially the result of mere luck. If Gallienus did not have to spend several years fighting off Germanic invaders, he could have confronted Postumus before Postumus had a chance to consolidate his authority. The invasion led by Aureolus in 265 mainly failed as a result of carelessness on his part. Gallienus had managed to defeat Postumus by retaking Raetia in 266, though Postumus reversed that defeat in 269. Postumus would not be in control of Mediolanum if Aureolus had not defected to him, and maintaining control of Mediolanum would have been more difficult for Postumus if Claudius II had not had to deal with the major Germanic invasion in the east. It was from Aurelian that Postumus would receive his first major challenge.

Aurelian did not take any action against Postumus until 275. For the first couple of years of his reign, he successfully contended with Germanic invaders. Then in late 272 and early 273, he turned his attention to recovering Egypt and the Asian provinces, which had become part of a breakaway empire similar to that of Postumus. Aurelian was able to bring the entire breakaway empire, known as the Palmyrene Empire, back under Roman rule in a matter of months. One action considered a key to his rapid victory over the Palmyrene Empire was that he had refrained from sacking the city of Tyana after taking control of it. As a result of the mercy he showed to Tyana, many other cities in the Palmyrene Empire opted to peacefully surrender. Aurelian conducted several other campaigns after this one, and then prepared to go to war with Postumus.

275
The war began in March 275, with Aurelian's armies invading Postumus' domain on three fronts: Baetica, Narbonensis and the Alpine provinces. Aurelian personally led the invasion of Narbonensis. At first, Aurelian's forces were successful on all three fronts.

By the middle of May, however, all three groups were losing momentum. The Alpine invasion actually turned out to be a complete fiasco, because Aurelian's spies had underestimated Postumus' defenses in the area. In Baetica and Narbonensis, the armies loyal to Postumus managed to slow down Aurelian's forces. The military itself in Postumus' realm was growing, because many people in those areas were strongly loyal to Postumus and voluntarily enlisting in order to defend him.

Postumus knew that fighting off Aurelian's all-out invasion would not be easy, so he decided to reach out to several Germanic tribes for help. He sent envoys to the Alamanni, Suevi, Marcomanni, and Quadi in late April. The envoys were instructed to propose an alliance between the tribes and Postumus' empire. The plan was for the tribes to invade Pannonia Superior, Pannonia Inferior, and Noricum; and in return, Postumus would consent to those tribes permanently controlling the territory of those three provinces, so long as they did not subsequently invade his territory. The Suevi declined the offer; but the other three tribes accepted, but only on the condition that Postumus develop and execute a workable plan for his own forces to invade another area under Aurelian's control.

In order to meet the demands of his potential allies, Postumus planned a massive invasion of Italy in May 275. In fact, he had already ordered some units to sneak into Italy, a few men at a time, between 271 and 273; so that he would have troops already in Italy should he ever deem any campaign in the Italian peninsula necessary. He decided this "sleeper army" would not be sufficient for a campaign of the size he was planning, however. He decided to send a large naval force to central Italy, order a land invasion from Transpadana, and have the sleeper army operate in the southern part of the peninsula. All three groups were to use scorched earth policies, and the invaders coming from the north and the center were to converge on Rome and sack it.

The invasion of Italy began on July 17, when the sleeper army began wreaking havoc in southern Italy. Postumus' forces began a seige of Rome on July 24, and broke into the city by August 19. The sack of Rome lasted until September 6, after which the forces under Postumus' command left and went on to plunder other cities in central and northern Italy. The invaders that entered Italy from the sea and from the north reached Raetia by November, although a quarter of them died along the way. The entire sleeper army was killed or captured in late September, just before it could escape to northern Italy.

The invasion of Italy was an important turning point in the war. It forced Aurelian to send some of his men to Italy and away from Postumus' empire, even to the extent of completely pulling out of areas that Aurelian's armies had already secured. Also, the success of the invasion caused the Roman military to begin losing faith in him; and in early October, Marcus Aurelius Probus and Faltonius Pinianus each declared themselves Emperor. It also convinced the Alamanni, Marcomanni, and Quadi that Postumus was worth supporting, and the three tribes began invading Pannonia and Noricum in late October 275.

Aurelian's soldiers and officers in Gaul and Spain continued to recognize him as Emperor, but they began losing confidence in him. One reason was because of how terribly Italy was devastated, and the other reason was because the campaigns in Gaul and Spain were progressing too slowly. The last straw came at the end of 275, when Postumus' forces and local resistance cells won back southern Spain from Aurelian in just a few weeks. When Aurelian's senior staff in Gaul learned of this, they decided that they had had enough of Aurelian. Aurelian's reign came to an end on December 27, 275: he was beaten, put in a cage, and deposed. Julius Asclepiodotus declared himself the new Roman Emperor, and his first act was to pull out of Gaul completely.

The Gallic Declaration of Independence
Up until this point, while Postumus had on the one hand refused to recognize the authority of the official Roman Emperors, and on the other hand made no effort to take over the entire Roman Empire; he had never actually declared his territory to be separate from Rome. This changed on January 14, 276, when Postumus issued the Declaration of the Independence of Gaul, Spain, and Britannia from the Roman Empire, which would be known commonly as the Gallic Declaration of Independence. The document declared these lands to constitute the Roman Empire of Gaul, which would be informally called the Gallic Empire.

The reasons stated in the Declaration for the Gallic Empire's secession were largely based on a "Two Romes" theory that had become popular among the people, although never endorsed by Postumus up until this point. According to the Two Romes Theory, the Gallic Empire had emerged as an internally stable and increasingly prosperous New Rome; whereas the remainder of the Roman Empire's territory constituted the Old Rome, which was still tormented by civil war, barbarian invasions, and economic hardships. The Declaration cited various successes of Postumus, various generals and provincial governors, and the people; as well as various failures of the Emperors and institutions of the Old Rome. Also, the Declaration stated that the Gallic Empire owed the Old Rome and its Emperors nothing, that the war had proven that the Gallic Empire was sustainable, and that reunification of the Gallic Empire with the Old Rome would be harmful to territories belonging to the Gallic Empire and not particularly beneficial to the Old Rome.

276
The Gallic Empire could have been at peace in 276. The Roman invasion of Gaul was done, central authority in the Roman Empire was breaking down, and Italy was in ruins. Yet the Gallic Empire continued to be at war with the Roman Empire during 276.

The reason for the continuation of the war was the Gallic Empire's alliance with the Alamanni, Marcomanni and Quadi. Although these three tribes enjoyed initial successes in their invasion of Noricum and Pannonia, Roman forces slowed them down; and by the middle of December 275, it was clear that the allied tribes were getting nowhere. Victorinus, who had remained in Raetia since he returned from Italy, asked Postumus to allow him to aid the Alammani by leading a campaign into Noricum. He received authorization from Postumus in early January. The invasion of Noricum began on January 9, 276. Thus, a new phase of the war began.

Victorinus' forces soon found themselves stalled in Noricum, so he asked Postumus for reinforcements. Postumus agreed to do so, even though this decision was poorly received by the people, the military, and the Senate. He also chose to personally lead the reinforcements, in an effort to boost their morale. The Gallic reinforcements began to move into Noricum on April 16. Thereafter, the Gallo-Germanic alliance steadily gained ground in Noricum.

Now after the sack of Rome, a republican government had emerged. As news of this development spread, republican factions came to power in other towns and cities that had been devastated during the Gallic invasion: some joined the new Roman Republic, while others chose to remain independent. For a while, Ascleiodotus and Probus ignored the republican states, but both chose to crush the republican movement after republican uprisings began occuring in areas that had been under their control.

Asclepiodotus and Probus easily overran the republican states during June 276. Unfortunately for both of them, their forces clashed several times. One such incident in the town of Lavinium (OTL Pomezia) that began on June 26 soon got out of hand, and resulted in a war between Asclepiodotus and Probus. By October, Probus gained the upper hand in this conflict. By November, Asclepiodotus realized he was going to lose northern Italy to Probus, so he fled Corsica. Then on November 25, Asclepiodotus was murdered, and Flavius Antiochianus took over the remainder of his realm. The conflict effectively had effectively ended by late December: Probus was firmly in control of northern Italy, and Antiochianus was not actively challenging him.

Gallo-Germanic gains in Noricum were slow but steady between May and November of 276. This was partially because Asclepiodotus could not send reinforcements to Noricum because he was contending with first the republics and then Probus. In October, however, Asclepiodotus had ordered all his forces in Noricum to move to Italy to fight Probus. Not all of the units complied, but enough of them did to make it possible for the alliance to make significant gains in November. The November Offensive ended when the allied armies reached the territory controlled by Pinianus.

277
After the alliance's momentum was stopped, it did not take long for Postumus to realize that he was now facing stronger armies than before. He also anticipated that Roman forces would be coming back toward Noricum soon, more numerous and less likely to be diverted than before. Also, he had maintained contact with Colonia Agrippina ever since he began his campaign, and he knew that both the Senate and the people were steadily losing patience with him. He had also been informed that Pinianus' forces had broken a long stalemate with the Quadi and retaken several towns during November. In other words, Postumus knew that his situation was fragile.

Postumus met with his generals and the leaders of the Alamanni, Marcomanni and Quadi in late December 276. During this conference, he proposed that the alliance try to get the Suevi to join them. After several days of negotiations, all three Germanic tribes agreed to Postumus' proposal. Then in January 277, the Suevi leaders met with the allied leaders and agreed to enter the war after several days of talks.

Suevi forces did not actually arrive in Noricum until late March, however. Before then, Roman forces managed to retake parts of Noricum. The allied forces were able to reverse this counteroffensive within a month after the Suevi joined the war. The alliance reached the Arrabo River (OTL Rába River) by the end of April. For over five weeks thereafter, there was a stalemate.

A new front was opened up in early June. A large number of allied troops had been sent from Noricum, around Pannonia, to the area on the opposite side of the Danube from southeastern Pannonia. On June 9, the allied forces crossed the Danube, and proceeded to seize territory. Then a month later, allied forces on the west side of Pannonia broke through the Roman lines and began to take large swathes of Pannonia Superior.

During August, the generals and soldiers who had up until this point recognized Probus and Pinianus were beginning to lose faith in their respective leaders. In the Balkans, Lucius Flavius Aper rebelled against Pinianus. Probus' realm, a general stationed in northern Italy and then the governor of Africa Proconsularis defected to Antiochanus. Pinianus and Probus found themselves in conflicts with Aper and Antiochianus that were not quickly resolved, so they did not send the necessary reinforcements. This allowed the Gallo-Germanic alliance to continue to gain ground in Pannonia. Finally, the alliance took Sirmium (OTL Sremska Mitrovica) and Bassianae, the last two cities in Pannonia under Roman control, during October. Once both cities had fallen, the allies were in control of all Pannonia. On October 24, 277, in a speech before troops from each of the five parties in the alliance, Postumus declared that the alliance was victorious.

Return to Colonia Agrippina
The truth was that the war with the Roman Empire was not over, even though the Germanic tribes that the Gallic Empire had allied with had taken control of all of Pannonia and Noricum. It was probable that one or more factions in the Roman Empire would launch a campaign to retake Pannonia and Noricum, and also probable that such a campaign could happen very soon. In spite of this, Postumus wrote a letter to the Gallic Senate stating that the war had ended, that he intended to return to Colonia Agrippina in the near future, and that he intended to begin ordering the Gallic troops to return home.

Postumus himself crossed the Gallic border on December 30, 277 and triumphantly entered Colonia Agrippina on January 22, 278. Some Gallic soldiers began returning home at the same time, but they were only a minority. The majority of the Gallic forces would remain there for several years. In the letter Postumus wrote to the Senate before returning to the capital, he did say that "some" of the Gallic soldiers would have to stay in Pannonia and Noricum for an extended length of time. He had euphemistically written that the purpose of their continued presence would be to "assist our Germanic allies in consolidating their control over Pannonia and Noricum", which meant that the Gallic forces were to help the Germanic forces fight off any Roman campaign to retake the conquered area and put down any rebellion staged by the locals.

Post-War Gallo-Germanic Relations
After the war ended, the leaders of the allied tribes began trying to get their civilian populations to migrate to Pannonia and Noricum. The Alamanni were the first to start the migration process. Their leaders started summoning their civilians in September 277, a few weeks before the war ended. Quadi civilians began moving into northwestern Pannonia in November 277. The Suevi and Marcomanni civilians did not begin migrating until March 278.

Postumus maintained close contact with all four tribes after the war. He promised the Alamanni safe passage through Raetia. He also ordered Victorinus, who remained in Pannonia until 279, to provide the tribes with advice in setting up states in the conquered provinces. Postumus also encouraged the leaders of the allied tribes to form alliances with other Germanic tribes, because he anticipated that the political climate in Gaul would prevent him from being able to come to their aid again.

Postumus and Victorinus hoped that the Germanic settlers would create Roman-style political entities. This was not to be. The new orders in Pannonia and Noricum were heavily influenced by Germanic law. Alamannia and Quadium were essentially oligarchies. Suevia could hardly be called a state at all: it was really a confederation of independent subgroups of the Suevi tribe. Marcomannia was nominally a monarchy, but it was really a council that was in control of the new nation; and many subnational rulers gained considerable levels of autonomy. In Alamannia and Marcomannia, the Roman bureaucracy was largely left intact. In Quadium, it was modified. In many places in the Suevian Confederation, it was completely dissolved in favor of new administrative structures.

The Pannonian War and the Norican War
In December 278, a new war broke out in Pannonia. After the Gallic War for Independence had formally ended, the civil war in the Roman Empire continued. In the east, Pinianus had managed to prevail over Aper by July 278. He was now seeking to take Pannonia back. The majority of the Gallic soldiers who had gone to Pannonia during the previous war were still there; and they, the local Suevian army, and a few units from the other three tribes fought back against the Romans.

For several months, the allied forces in Pannonia were just enough to keep the Romans from getting anywhere. Then forces affiliated with Antiochianus invaded Alamannia in March 279. The Alamannian leaders sent a delegation to Colonia Agrippina, to ask Postumus to send troops back into Pannonia and Noricum. The Alamannian leaders knew that the Senate and people of Gaul would not tolerate another direct war with the Roman Empire, so they instructed their delegates to ask that the requested Gallic troops be deployed to the interior of Pannonia and Noricum to maintain order there, thereby freeing up Germanic soldiers to fight the Romans. Even this was unacceptable to the Senate. Postumus denied the Alamannian request and told the delegates that Alamannia and the other three Germanic states would have to fight off the Romans without any Gallic forces that were not already there.

The Pannonian War had ended by July 279. Pinianus had failed to retake any territory in Pannonia, and now he was facing another rebellion, this time from a general named Publius Aelius Aelianus. Thereafter, the allies sent additional troops to Alamannia to fight Antiochianus' forces, who had managed to make modest gains. For a couple of months, there was a stalemate. Then in September 279, the allies discovered a weakness in the Roman lines, broke through, and then began pushing Antiochianus' armies out of Alamannia. By December, all of Alamannia had been retaken.

Antiochianus began to lose support after his invasion of Alamannia failed. Some of his generals changed their allegience to Probus; while others began to rally behind a new candidate for the throne, a man named Lucius Valerius Messalla, the governor of Africa Proconsularis. Meanwhile, Pinianus, realizing his rule was coming to an end, peacefully surrendered to Aelianus in exchange for being allowed to retire. By 280, there were four major contenders for the Roman throne. All four made eliminating each other their first priority. No Roman faction would cause trouble for the Gallic Empire or its Germanic allies for many years.

Administrative Overhaul
In 278, Postumus spent several months formulating a significant modification of the Gallic administrative structure. He formally announced his reform plan to the Senate on August 13, 278, and the Senate ratified it on August 21.

The administrative reform had several features:
 * The province of Tarraconensis was to be split into six provinces, the eastern part of Lusitania was to be made into a new province called Vettonia, and the eastern half of Narbonensis was to become a new province called Massiliensis.
 * The relationship of the provincial governors to the military was to be modified. In the past, governors had been in charge of all military forces within their respective provinces. Hereafter, governors would retain control over a percentage of the forces within their respective provinces (such a percentage would vary by province and be determined by the Emperor), but many of the units in each province would be transferred to the command of a new type of official called a dux. The provinces would be grouped into military districts, with two or three provinces in each district; and within each military district, the dux would be responsible for the military forces over which the provincial governors did not retain command.
 * The classification of the majority of the provinces was to be changed from imperial to senatorial. The difference between the two classes of provinces was who appointed the governors: governors of imperial provinces were appointed by the Emperor, and governors of senatorial provinces were appointed by the Senate. When the Gallic Empire initially seceded from Roman rule, only Baetica and Narbonensis were senatorial; whereas now, only Germania Superior, Germania Inferior, Raetia, Massiliensis, Belgica, Transpadana, the Alpine provinces, Britannia Inferior, and three of the new provinces in northern Spain were to be imperial.
 * Changes were to be made to the civil service. In particular, the imperial postal service (which had been formed from the local branches of an identical Roman institution at the start of Postumus' reign) and the department dealing with correspondence between Colonia Agrippina and officials stationed elsewhere in the empire were to be enhanced.

Whereas the purpose of the earlier political reforms was to provide an alternative to armed rebellions against the Emperor, this new reform package was intended to make attempts by provincial governors to rebel more difficult. The partitioning of the larger provinces meant that the governors of the new provinces would have fewer troops under their command, and the introduction of the duces would further reduce the number of troops under the command of each governor. At the same time, the governors would retain some authority over the military forces in their respective provinces in order to prevent the duces from becoming too powerful. The civil service reforms were meant to ensure that the empire would be as integrated as possible. Postumus' reason for reclassifying the majority of the provinces stemmed from a belief that he had held for several years: that the Gallic Empire's future lay in a degree of co-operation between the Senate and the Emperor.

Another important event in the history of Gallic law came fourteen months later. In October of 279, Postumus asked several scholars to carry out a project of codifying all the laws of the Gallic Empire. Their task was not completed until after Postumus' death.

Death
Postumus designated Victorinus as his successor late in 278. Victorinus had proven himself to be a skilled general ever since Postumus began his rule. There were several other fine generals in the Gallic army: Postumus chose him mainly because of his role in the Gallic War for Independence.

Postumus' health began to deteriorate in early 279. In October, he recalled Victorinus to Colonia Agrippina to prepare him to take control of the empire. Victorinus arrived at the capital on January 11, 280. During the following months, Postumus heavily involved Victorinus in the administration of the empire.

On May 17, 280, Postumus tripped and fell after leaving a Senate meeting. He suffered a head injury as a result of that fall, and died on May 20, 280.

The Great Roman Civil War
Main article: Great Roman Civil War

The civil war that began in the Roman Empire in the summer of 276 continued long after the Gallic War for Independence, the Pannonian War, and the Norican War ended.

280 began with four generals fighting each other for control over what was left of the Roman Empire; namely Probus, Antiochianus, Aelianus, and Messalla. 280 ended with the elimination of Probus and Antiochianus from the war. Messalla gained control of all the territories that Antiochianus had ruled and most of those that Probus had ruled. Messalla's strategy was to use diplomacy to persuade generals and provincial governors to join him. Once Messalla had gained enough support, he launched an assult on the core of Antiochianus' realm. The campaign was successful, Antiochianus committed suicide, and Messalla took control of all of Antiochianus' territories in a matter of days. Less than two months thereafter, Probus was ousted and his regime was taken over by several of his generals, who agreed to side with Messalla.

During 281, Messalla fought to wrest control of the provinces of Dalmatia and Asia from Aelianus. For most of the year, he made little progress: by September, he had only managed to take control of a third of Dalmatia, the Dodecanese, and the area surrounding a small bay in Asia. In September, however, he sent more troops to Dalmatia, which enabled him to take over the majority of the province in a matter of weeks. At roughly the same time, Messalla's forces began to steadily gain ground in Asia.

Another development that took place in 281 was that the governor of Cappadocia, frustrated by the complete breakdown of central authority in the Roman Empire, refused to recognize any of the contenders for the purple. From Aelianus' point of view, the Cappadocia had seceded from the Roman Empire in everything but name. Aelianus launched a large invasion of Cappadocia, but Cappadocia managed to resist Aelianus.

The war finally ended in 282. During the spring, the governor of Lycia and Pamphylia abandoned Aelianus for Messalla. This enabled Messalla to win several important victories in Anatolia. This in turn prompted defections by several generals from Aelianus to Messalla. Meanwhile, Cappadocia was withstanding Aelianus' invasion fairly well, and the border province of Osroene began to rebel against Roman rule. All these events depleted Aelianus' remaining forces. Finally, on May 6, Messalla's forces won the Battle of Pergamon, which convinced all of Aelianus' remaining generals and provincial governors to recognize Messalla. Aelianus himself surrendered on May 30, thereby bringing an end to the war.

After the war ended, Aelianus spent two months under house arrest while Messalla figured out what to do with him. On August 6, Messalla met Aelianus in Thessalonica and presented him with a plan for sharing power. Messalla's plan, known as the Treaty of Thessalonica, nominally made Aelianus a secondary Emperor and gave him authority over most of Anatolia and the Balkans, but in reality was designed to make Aelianus Messalla's puppet. Aelianus signed the treaty because the only alternative was for him to be executed.

The Reign of Victorinus
On May 21, 280, the day after Postumus died, Victorinus addressed the Gallic Senate. He informed them that in accordance with Postumus' wishes, he would succeed Postumus as the new Gallic Emperor. The day after that, he announced his succession to the people. The funeral for Postumus was held the following day.

The Pannonia and Noricum Military Presence Scandal
By the time Victorinus became emperor, the Gallic Empire still had a military presence in Pannonia and Noricum. Victorinus knew that the military presence was becoming increasingly unpopular among the Gallic people, but he deemed it necessary to keep troops in Pannonia and Noricum for as long as possible to protect the nascent Germanic states. In an effort to delay political pressure to end the military presence, Victorinus recalled 400 soldiers, but then quietly sent 400 new soldiers to replace them. The recalled soldiers began returning home in October 280, and the replacement soldiers were sent to Pannonia and Noricum at the same time. Initially, Victorinus’ actions seemed to have served their intended purpose: both the people and Senate of Gaul were unaware of what had happened. At the same time, the rise of Messalla in the Roman Empire provided Victorinus with a justification for keeping troops in Pannonia and Noricum.

In the summer of 281, Victorinus recalled another 400 soldiers, but had 800 new soldiers quietly sent in. The net increase did not go unnoticed by the inhabitants of the Germanic nations. Unbeknownst to Victorinus, the Gallic military presence in Pannonia and Noricum was becoming unpopular among the people of those regions. After the new forces arrived, riots ensued, with the majority of the rioters being of Germanic ethnicity. Word of the unrest trickled across the border. Then on November 12, 281, the Gallic Senate received a letter from the king of Marcomannia, in which the king expressed displeasure with the increase in the military presence and demanded a substantial reduction. The letter was read on the Senate floor four days later. Victorinus, who was in the Senate chamber when the letter was read, was forced to admit his actions. The majority of the senators were furious. Word quickly spread to the people, and the people were equally angry.

On December 19, 281, the Senate informed Victorinus that it would vote on whether or not to depose him he did not recall at least two thousand soldiers from Pannonia and Noricum without replacement by March 1, 282. Thereafter, Victorinus quickly began recalling units. On January 8, 282, Victorinus appointed thirty close allies of his to the Senate. He did this because he was worried that the soldiers would not arrive in Gallic territory soon enough, and he knew that the Senate would be hostile to him anyway. Many senators saw stuffing the Senate as a new reason to depose him, even though the Senate knew to expect the recalled army units to begin arriving in Gallic territory by late February. The Senate voted on a motion to depose Victorinus on March 7, 282. The motion failed by a vote of 109 to 121.

Although the effort to depose Victorinus failed, the Senate remained hostile to Victorinus until early 283, when Victorinus expelled fifty senators who had persistantly opposed his agenda and replaced them with reliable partisans. Victorinus honored his promise not to replace the forces he had recalled from Pannonia and Noricum, but he did not recall any more troops until 285.

Domestic Policies
One thing that Victorinus inherited from Postumus was a project to codify all the laws of the Gallic Empire. After the committee had completed its work, Victorinus appointed himself to the committee to personally oversee revisions to the codification. The changes Victorinus made involved eliminating most of the republican vestiges the Gallic Empire inherited from the Roman Empire and giving official legal sanction to the office of emperor. The official title of the emperor was to be Princeps Civitatis (First Citizen). The Senate would still exist, and it retained the authority to depose the First Citizen; but it was still largely a puppet of the First Citizen, as the First Citizen had absolute control over its membership. After the revised version of the codification was completed, Victorinus submitted it to the Senate for ratification. The Senate ratified the codified laws on March 28, 283.

As First Citizen, Victorinus was the chief priest of the Gallic state religion. During the early 280s, Victorinus used this authority to inject Celtic themes into the state religion. One change he made was by promoting more frequent use of the Celtic names for deties worshipped by both the Gauls and Latinized people: for example, Mars was henceforward known as Letus, and Apollo became known as Grannus. Another change Victorinus made was injecting animistic themes into the state religion. Most other aspects of the state religion that were inherited from Rome were left unchanged.

During the late 280s, Victorinus began promoting trade with the Germanic tribes. It was primarily the state that conducted external trade, as private merchants had little interest in doing business with the Germanic tribes. The state paid craftsmen to produce goods that were then transported and sold east of the Rhine.

During most of his reign, Victorinus continued Postumus' policy of maintaining a relatively sound currency. The main exception was during the time that the Senate was challenging his rule: in an effort to buy the loyalty of the army, Victorinus ordered the minting of a large number of antoninianius coins to finance large pay raises for all army units stationed in and around Colonia Agrippina. These coins had silver contents of around half of that of a normal antoninianus. This resulted in inflation in northeastern Gaul.

Foreign Relations
Postumus had hoped for the Gallic Empire to eventually annex the Roman province of Mauritania Tingitana. Victorinus encouraged the governor of Baetica to try to establish economic and cultural links with Mauritania Tingitana, the intended purpose being to encourage Mauritania Tingitana to abandon the Roman Empire for the Gallic Empire. The Mauritanian people would not want anything to do with the Gallic Empire until long after the death of Victorinus, however.

Under Victorinus, the Gallic Empire continued to have amicable relations with Alamannia, Marcomannia, Suevia, and Quadium. Victorinus also began building diplomatic relations with other Germanic tribes. Meanwhile, the Quadian government began working to build a partnership with the Gepids and Iazyges, who lived east of Pannonia.

Victorinus withdrew the remaining Gallic troops from Pannonia and Noricum between 285 and 286, because it was increasingly clear that Rome's first priority was simply to recover from the worst civil war in its history. Also, during the late 280s, Victorinus began promoting trade with the Germanic nations and tribes.

The Death of Victorinus and the Election of His Successor
Victorinus contracted pneumonia in November 293, and he died on December 6 of that year. He had failed to name a successor, so the responsibility of selecting the new First Citizen of Gaul fell on the Senate. The Senate was by this time almost entirely filled with consistent allies of Victorinus, so the main candidates for the throne were men from Victorinus' inner circle. By January 294, four candidates that emerged were a senator named Gaius Pius Esuvius Tetricus; Ulpius Cornelius Laelianus and Lucius Desticius Bonosus, both generals and veterans of the Gallic War for Independence; and Marcus Gavius Carausius, the governor of the province of Germania Superior.

Issues
One issue that arose in the Senate after the death of Victorinus was the relationship the Senate would have with the new First Citizen. By the time of Victorinus' death, there were still senators who were willing to openly challenge Victorinus, although Victorinus was always able to stifle opposition by expelling troublesome senators and stuffing the Senate with his partisans. After Victorinus died, a group of senators who had challenged him on several occasions asked that the new First Citizen be willing to co-operate with the Senate and refrain from casually stuffing the Senate with his supporters. This faction came to be known as the Postumians, because they claimed that the constitutional structure established by Postumus had been eroded by Victorinus and needed to be safeguarded. A few of Victorinus' supporters sided with this faction: they recognized that any future emperor could do to them what Victorinus had done to his opponents. The majority of the senators who had supported Victorinus were content with the status quo, however; and those content with the status quo came to be known as the Princepists, because they supported the concept of a powerful First Citizen (Princeps Civitatis).

For many senators, a key factor in the decision of which imperial candidate to support was what kind of relationship each candidate was likely to be willing to have with the Senate. Tetricus was a senator, so many senators in the Postumian faction anticipated that he would be sympathetic to the Senate's interests. Bonosus, Laelianus, and Carausius each appealed to many of the Princepists, because all three of them had been on good terms with Victorinus. Since Bonosus and Carausius had never worked closely with the Senate, the Postumians did not expect either of them to be particularly interested in dealing with the Senate as an equal partner. Some of the Postumians supported Laelianus: even though Laelianus had never worked directly with the Senate, he had been friends with Postumus; so the Postumians who supported him believed that he would be sympathetic to Postumus' vision of genuine co-operation between the emperor and the Senate.

The relationship between the new First Citizen and the Senate was not the only issue. There were many senators whose main concern was which candidate would be the best military leader. All four candidates had served in the army, but Laelianus and Bonosus had far more distinguished careers than Tetricus and Carausius.

Another issue was the age of each candidate. Laelianus and Bonosus were 62 and 67 years old, respectively. On the other hand, Tetricus was 53 and Carausius was 36.

The Election
On February 14, all four candidates delivered speeches before the Senate, in which they described the policies they would implement if elected. Tetricus and Laelianus promised to refrain from stuffing the Senate with their supporters whenever doing so was convenient for them. Carausius, on the other hand, said that he considered it proper for the Senate to defer to the First Citizen's wishes. Bonosus stated that it was acceptable for the First Citizen to stuff the Senate with his allies, and that refraining from doing so was only a courtesy. When addressing the subject of military leadership, Laelianus and Bonosus both referred their roles in the Gallic War for Independence. Tetricus, who did not have as much military experience, promised to heavily rely on the advice of his generals; and he said that Laelianus and Bonosus were both too old and that Carausius' military career was unexceptional. Tetricus and Bonosus also promised to continue expanding diplomatic relations and trade with the Germanic states and tribes, whereas Laelianus and Carausius did not mention that issue.

The Senate scheduled the election for March 1. During the latter half of February, the Senate spent much of its time debating who to elect. According to the Senate's rules of proceedings, a candidate only needed to receive a plurality of the votes, not a majority. As the election approached, it was clear that none of the candidates would receive a majority of the votes. There were 250 senators; and during the week after the candidates addressed the Senate, it seemed that Tetricus would receive approximately 80 votes, Laelianus and Bonosus would each receive 60 votes, and Carausius would receive 50 votes. This changed on February 23, when Bonosus announced that he was ending his campaign and endorsing Laelianus. The majority of the senators who had intended to vote for Bonosus immediately threw their support behind Laelianus. The supporters of Tetricus and Carausius reacted by spending the final days of February discussing the formation of a coalition to defeat Laelianus. Meanwhile, Tetricus himself reached out to Laelianus' supporters to negotiate. On February 27, several of Laelianus' supporters agreed to vote for Tetricus on the condition that he would heavily rely on Laelianus and Bonosus for advice on matters concerning the military. The next day, several of Carausius' supporters agreed to vote for Tetricus on the condition that Tetricus would designate Carausius his successor immediately following his election; and when Tetricus was informed of this deal, he agreed to honor it, even though he personally disliked it.

The election for the new emperor was held on March 1, 294. Tetricus received 102 votes, Laelianus received 95 votes, and Carausius received 53 votes. As soon as it was announced that Tetricus won, Tetricus declared Carausius his successor. The next day, Tetricus gave a speech in Colonia Agrippina in which he announced his election as First Citizen and his appointment of Carausius as his successor.

The Reign of Messalla with Aelianus
After the Great Roman Civil War ended, the Roman Empire was devastated. Many cities in Italy, Africa, the western Balkans, and western Anatolia were ruined. Central and northern Italy were a wasteland: the Gallic army conducted a scorched earth campaign there in 275, and fighting between various candidate emperors had devastated the area many times over after that. The size of the Roman army had fallen by almost 19% since 275, from 240,000 men to 195,000; and over the same time period, urban warfare and scorched earth policies had claimed the lives of 400,000 civilians, food shortages led to an additional 650,000 civilian deaths, and other effects of the Gallic War for Independence and the Great Roman Civil War resulted in the death of another 100,000 civilians. Altogether, approximately 1.2 million inhabitants of the Roman Empire died between 275 and 282. Hundreds of thousands were also left homeless or otherwise in severe poverty. Also, the Great Roman Civil War had dramatically exacerbated the hyperinflation that had already been a problem for decades.

That was the Roman Empire that Messalla found himself in control of on June 1, 282. Messalla also faced a political problem: he had deemed it necessary to share power with Aelianus, but he believed that he could never trust him. Messalla spent his entire reign healing the lands that were still under Roman control, and working to prevent a climate of political instability like the one the empire had endured for decades would not return.

Reconstruction Program
Messalla set up a massive program to rebuild infrastructure and cities in the areas that suffered most during the war. The program was created while the war was still in progress, but it was not until after the war came to an end that substantial amounts of money and resources were channelled into the program. After the war ended, Messalla encouraged soldiers who resigned and returned home to join the local branches of the public works program.

The program was paid for by high taxes and further increases in the money supply (albeit at a slower pace than during the war). The public works program employed many men who might otherwise have had trouble finding work, and it was successful in rebuilding many cities, but the empire's economy remained stagnant for a long time.

The End of the Roman Senate
By the time the Great Roman Civil War ended, it was common knowledge among the Roman political establishment that the Gallic Senate had grown increasingly willing to challenge the authority of the Gallic Emperor. Messalla found this troubling. He feared that the news of the Gallic Senate's growing assertiveness would inspire the Roman Senate to be willing to challenge his authority. It seemed unlikely, as the Roman Senate had been stripped of all real power nearly three centuries before, and its evacuation of Rome during the Gallic sack of the city had cost it what little prestige it had left; but Messalla thought it best not to take any chances. Thus, Messalla disbanded the Roman Senate on January 4, 283.

After the Senate was dissolved, some senators were put on trial for various charges (usually trumped-up), and others were forced out of public life or demoted to low-level offices, but most were assigned new responsibilities and allowed to retain the title of senator. The term "senator" was redefined: instead of referring to a member of a legislative body, it now referred to a holder of any high-level office. Messalla himself took the title of Senator Supremus (Supreme Senator) in 285.

The Osrinian War
During the final months of the Great Roman Civil War, the eastern province of Osroene rebelled against Roman rule. The rebels seized control of the provincial capital, and then quickly convinced the Emperor of Persia to send troops to help them fight off the Romans. After the Persians arrived, they and the Osrinian rebels managed to drive the Roman forces out of most of Osroene.

Messalla opted to abandon Osroene completely. He knew that the Roman army and the people were tired of war, and would have little desire for a war against Persia over one province. He did intend to retake the province later, and he and Aelianus both stationed forces under their command in the provinces bordering Osroene after the civil war ended.

In January 286, Messalla decided that the time was right to begin a campaign against Osroene. He met with Aelianus in Dyrrhachium to discuss plans for the invasion. They planned to first double the number of soldiers present in the provinces bordering Osroene. Those units were all to attack Osroene on the same day. Before that was to occur, however, Messalla was to send five legions and twenty auxiliary units eastward from Syria Coele, and Aelianus was to send three legions and ten auxiliary units eastward from Syria Phoenicia: the plan was for some of those units to attack Osroene's southern border, and the majority of the units to invade Persia itself. Aelianus also offered to ask the king of Armenia for support, and Messalla permitted him to do so. The king of Armenia declined to get involved in the conflict, however.

The invasion of Osroene began on August 11, 286. It turned out to be a failure for Messalla and Aelianus. The two emperors did not know just how determined the Persian emperor was to hold on to his new ally. Persia had maintained a strong military presence in Osroene ever since 282. He had also made a mutual defense pact with the Arab kingdom of Lakhm in 284, thereby giving him even more strength against Rome. Thus, Persia was well-prepared both for an invasion of Osroene and for an attack on its own territory. The Roman forces crossing the desert were intercepted before they entered Persian territory and were forced to retreat. Most of the units that invaded Osroene were likewise driven away, although a few were trapped and wiped out or captured. Then, after the Persian and Osrinian forces repelled the Romans, they began invading Roman territory. By mid-October, the Persian and Osrinian armies had advanced all the way to the Mediterranean. Fortunately for the Roman Empire, the king of Armenia found Persia's and Osroene's rapid advance troubling, so he sent troops to aid the Romans. By early December, Rome and Armenia had pushed Persia and Osroene back to the Euphrates. Before the Roman and Armenian forces could advance farther, however, Persia attacked Armenia. Armenia was not strong enough to both aid Rome and defend itself, so it surrendered on December 14, 286. Aelianus and Messalla surrendered a week later.

A peace agreement was concluded by the end of January 287. The Roman Empire was to cede the province of Mesopotamia to Osroene. Armenia was to cede some of its southern territory to Persia. Both states had to pay reparations to Persia and Osroene: the reparations paid by Rome came mainly in the form of food, livestock, horses, and tools as Rome had little else to give; while the reparations paid by Armenia were mainly monetary in nature. Armenia was also sworn to neutrality in all future conflicts between Rome and Persia.

The Eastern Rebellion
During 287, the Persians and Osrinians collected goods from the Roman provinces of Syria Coele, Cilicia, southern Galatia, and northern Syria Phoenicia as reparations for the Roman invasion. All of these provinces were in the Dominium Caesaris (Dominion of the Caesar), the area ruled by Aelianus. In some areas, Persian and Osrinian troops were allowed a direct presence on Roman soil, and collected goods directly from the locals; while in other areas, Roman soldiers collected goods from civilians and then handed them over to Persian and Osrinian units. The Persian and Osrinian soldiers plundered the towns and cities they occupied directly without restraint; whereas in the places where Roman soldiers acted as intermediaries, the Roman soldiers usually left businesses and households with just enough to be able to start recovering.

The volume of goods that Persia and Osroene demanded was large enough that the transfer of those goods was a severe blow to the economies of those provinces. Many businesses had their tools confiscated, and were unable to operate until they could obtain new tools. Many farmers had all of their harvests beyond what they needed to feed themselves and their families confiscated; and had their plows taken as well, so that it would be harder for them to grow food the following year. During 287, approximately 54,000 people in the areas where the confiscations took place died of starvation as a result of food shortages. Also, many people who were desperate for food turned to crime, and food riots broke out in many cities; and crime and rioting led to another 8,000 deaths. The provincial governors had their own farms that were left untouched by either the Persians and Osrinians or Roman intermediaries, and they tried to distribute some of the food produced there to the people, but this did little to alleviate the food shortages.

The confiscation of goods by Persia and Osroene ended by the beginning of 288; but problems in Anatolia not only continued, but spread westward. Farmers and craftsmen still lacked various tools they needed to produce goods. Thus, the food shortages continued, as did crime and rioting. Then in May, Aelianus issued a decree that mandated the transfer of food and supplies from Lycia and Pamphylia, Bithynia and Pontus, and Thrace to the areas affected by confiscations. He also ordered transfers from northern Galatia to southern Galatia. This command was not well received by the people of the affected areas. In many areas, people tried to hide tools in order to prevent them from being confiscated. In many cities, riots broke out, the target of the rioters being local officials. In some cities, local officials defied Aelianus: some out of fear for their own safety, others out of sympathy for the people. Aelianus tried to appease the people by revising his command to provide for monetary compensation for the confiscated goods, but this satisfied few people.

Messalla Betrays Aelianus
Unrest in Anatolia and Thrace continued and grew increasingly severe for months. A turning point came in October. Messalla had never trusted Aelianus, and he decided to use the disorder in the east as a pretext to eliminate him. Messalla issued orders to units in Asia and Insulae (provinces that he directly ruled) to invade Thessalonica and arrest Aelianus. He issued similar orders to units under his command stationed throughout the Balkans. Messalla claimed that at best, Aelianus had simply lost control of the situation; and that at worst, Aelianus would use the problems in the Dominium Caesaris as an excuse to rebel against Messalla.

Messalla's forces began to attack Aelianus' forces in Macedonia in November 288. Aelianus had been preparing for Messalla to turn on him as early as August, so his forces were able to resist somewhat. Then on November 12, Aelianus renounced the Treaty of Thessalonica and declared his intent to overthrow Messalla. Unfortunately, there was little Aelianus could do. The Treaty of Thessalonica had granted Messalla authority over 40% of the military forces stationed in the Dominium Caesaris, and Messalla had kept large numbers of units in Asia and Insulae. Thus, Messalla's forces were able to surround Thessalonica by November 29. When Aelianus saw that the city was surrounded, he instructed the forces defending the city to surrender, and then hanged himself.

After Aelianus surrendered and committed suicide, three generals assumed provisional control over the Dominium Caesaris. They immediately turned their attention toward restoring order in Thrace and Anatolia. By March 289, the resistance had been brutally crushed. Civil officials and army commanders who had participated in the resistance were given show trials and either executed or imprisoned.

Replacing Aelianus
Even though Messalla had used the system established in the Treaty of Thessalonica as a means of controlling and eventually eliminating Aelianus, Messalla also intended for the succession procedure to be permanent. Therefore, after the death of Aelianus, Messalla announced that the Dominium Caesaris would continue to exist, a new Caesar would be chosen to rule the territory, and that new Caesar would succeed Messalla as Supreme Senator (the title which Messalla had made the official title of the Roman Emperor) after Messalla's death.

Messalla spent the first months of 289 considering who to appoint as Caesar. By March, one man he was seriously considering was Diocles Valerius (known in OTL as Diocletian). Diocles was a general who had served with distinction under Aurelian and Pinianus during the Great Roman Civil War. He was one of the first two generals stationed in Dalmatia to defect to Messalla after the fall of Antiochianus and Probus. Moreover, not only was Diocles both an exceptional and loyal military leader, but he was also a competent administrator. He had held multiple civil offices during the 270s and 280s, including four provincial governorships — one under Aurelian, two under Pinianus, and one under Messalla — and highest administrative position in the public works program between 285 and 287.

Despite Diocles' exceptional record, Messalla ultimately chose not to appoint him Caesar. Messalla considered Diocles too ambitious, and anticipated that Diocles would seek an opportunity to rebel. Instead, Messalla chose Marcus Aurelius Valerius Maximianus (Maximian), a general and a longtime friend of Diocles. Maximian was less educated and less distinguished as an administrator than Diocles, but he was a competent military leader, and he had never demonstrated any sort of political ambition. Messalla assumed that Maximian could compensate for his own weakness as a political leader by relying on Diocles' counsel.

Messalla appointed Maximian Caesar of the Dominium Caesaris on March 22, 289. Since Messalla trusted Maximian, he was willing to give him an actual degree of autonomy. On July 2, Messalla and Maximian met in Thessalonica signed a new treaty on the relationship between the Supreme Senator and the Caesar. The new treaty, known as the Second Treaty of Thessalonica, guaranteed Maximian a degree of actual autonomy. Messalla would only have direct control one quarter of the military forces in the Dominium Caesaris, Messalla's veto of laws or appointments made by Maximian could be overridden with the concurrence of three fifths of the governors of the provinces in the Dominium Caesaris, laws made by Messalla would only be binding in the Dominium Caesaris if they were approved by the governors of one fifth of the provinces therein, and any veto by Messalla of appointments made by Maximian to the regency committee could be overridden with the concurrence of only two fifths of the provincial governors from the Dominium Caesaris. Also, the borders of the Dominium Caesaris were expanded slightly: the province of Asia, previously directly ruled by Messalla, was divided into the new provinces of Ionia, Caria, and Phrygia; and Caria and Phrygia were placed in the Dominium Caesaris.

New Administrative Structure
During 290, Maximian and Diocles worked on a plan to overhaul the Roman Empire's administrative and military hierarchies. Their goal was to develop a system that would make it harder more difficult for army commanders or provincial governors to rebel against the emperor.

The plan was partially modelled on the Gallic administrative reforms that Postumus had enacted in 278. The plan of Diocles and Maximian called for most of the Roman Empire's provinces to be partitioned. These smaller provinces were to be grouped into military districts, each overseen by a military officer called a dux. As was the case in the Gallic Empire, some of the military forces in each province would be commanded by the governor, and some would be commanded by the dux. Yet Diocles' and Maximian's plan went even further: they proposed grouping the provinces into praetorian prefectures, each one ruled by a praetorian prefect. (The praetorian prefects were essentially the heads of the emperor's bodyguards, but Diocles and Maximian proposed for the office to be transformed into more of an administrative office.) Each praetorian prefect would have the power to appoint provincial governors, have command of some of the military forces in each province under his jurisdiction, and have administrative and judicial powers within his praetorian prefecture.

Maximian was able to implement part of the administrative reform plan on his own initiative within the Dominium Caesaris. He had almost complete authority over the portion of the military forces within the Dominium Caesaris that were under his command, so he was able to set up military districts, appoint duces to oversee the districts, and transfer command of a percentage of the military forces in each province from the governor to the dux without having to authorization from Messalla; and he did this between July 290 and May 291. The rest of the proposal did have to be approved by Messalla: Maximian did not have the authority to create new provinces, nor did he have the right to appoint praetorian prefects. Also, Diocles and Maximian intended for their administrative overhaul to be applied throughout the empire, but only Messalla could implement it outside the Dominium Caesaris. In February 292, Messalla issued an edict in which he announced his approval of the Diocles-Maximian plan and declared that it would be implemented in full. The edict was ratified by the required number of governors in the Dominium Caesaris by June 292.

After the new political and military subdivisions were established, Diocles began developing a second set of administrative reforms. (Maximian was far less involved in developing this plan than he was in the development of the first one.) This plan focused on overhauling the imperial bureaucracy. Diocles developed the expansion of some existing departments, including the Cursus Publicus (the postal service) and the department that oversaw the imperial treasury and handled taxation. He also proposed the creation of several new departments, including one responsible for drafting legal documents and keeping records, one responsible for handling the many legal petitions the Supreme Senator and Caesar received, and one to handle correspondance between government officials. Diocles also suggested that the public works program Messalla had created at the start of his rule be expanded.

Maximian accepted and began implementing most of Diocles' second administrative reform plan in 294. The civil service reforms were such that they could be implemented in the Dominium Caesaris without needing to also be implemented in the rest of the Roman Empire, so Maximian did not seek Messalla's approval carrying out the reforms.