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Messalla was born in central Italy on August 14, 241. He hailed from a branch of the Gens Valeria, a very old Roman family. His father, Lucius Valerius Poplicola Balbinus Maximus, held numerous civil and military offices during the mid-3rd century. Growing up, Messalla received the best education available in the Roman Empire.
Throughout the 260s, Messalla held a variety of low-level civil offices in Italy.
Great Roman Civil War
After Probus declared himself Roman Emperor, Messalla threw his support behind Probus. In January 278, Probus appointed Messalla governor of Africa Proconsularis after Probus' forces had taken over the province.
During 279, Messalla became disillusioned with Probus, and on November 1 of that year, he declared himself Emperor. During the few weeks that followed, several generals who who had become disillusioned with both Probus and Antiochianus defected to Messalla. On January 4, 280, the governor of Numidia joined Messalla. For several months, Messalla focused on governing the areas under his control, rather than gaining territory. He ordered all the units that had defected to him to come to Africa Proconsularis and Numidia. During the summer of 280, Messalla began sending out envoys to persuade generals and provincial governors to join him.
By September 280, most of the generals in central Italy had joined Messalla's side. Messalla then ordered those forces to invade Corsica, the core of Antiochianus' territories. By that time, Antiochianus' regime was already imploding; so when the invasion of Corsica began, many of Antiochianus' forces defected to Messalla. By the end of the month, Antiochianus had killed himself and Messalla had taken over all of his territories. The following month, Probus was overthrown, and Messalla assumed control of the majority of his territories.
After the downfall of Probus and Antiochianus, Messalla fought Aelianus for control of the Roman Empire's eastern provinces. Messalla's forces made gradual gains during 281. In 282, Messalla won several important victories that prompted provincial governors and generals throughout Anatolia and the Balkans to recognize him as emperor. Finally, Aelienus surrendered on May 30, 282, thus ending the Great Roman Civil War.
Rule as Emperor
Establishment of the Diarchy
During the war, Messalla offered Aelianus a power-sharing agreement in order to persuade him to surrender. Under the terms of the agreement, Aelianus would be a Caesar (a subordinate co-emperor). As Caesar, Aelianus would administer an autonomous region within the Roman Empire that would be called the Dominium Caesaris (Dominion of the Caesar), and he would succeed Messalla as the senior emperor. Aelianus rejected Messalla's offer.
After the war was over, Messalla decided to implement his power-sharing plan; although by this time, his main reason for doing so was a perceived need to appease former supporters of Aelianus who might otherwise have not defected to him. He had originally envisioned this system as one of genuine cooperation with Aelianus, but he modified the plan to make it a means of controlling Aelianus.
The power-sharing and succession plan, known as the Diarchy ("rule by two"), entered into force on August 6, 282, with the signing of the First Treaty of Thessalonica. The terms of the treaty were as follows:
- Messalla was to be the sole Augustus (senior Emperor) in the Roman Empire. Aelianus would be the sole Caesar.
- The Dominium Caesaris would consist of the provinces of Syria Phoenicia, Syria Coele, Mesopotamia, and Anatolia and the Balkans (except for Dalmatia, the Aegean Islands, the province of Asia, and Cyprus); and also Cappadocia and Osroene upon their reconquest.
- Authority over the military in the Dominium Caesaris was to be split between Aelianus and Messalla, with Aelianus having authority over three fifths of the military forces stationed in the area, and Messalla having authority over the other two fifths.
- Laws made by Messalla were to apply throughout the empire, and were to supersede any laws made by Aelianus. Moreover, Messalla reserved the right to nullify any law or gubernatorial or other appointment made by Aelianus; although Messalla's veto could be overriden by the unanimous concurrence the provincial governors within Aelianus' domain.
- As Caesar, Aelianus was to succeed Messalla as Augustus upon the latter's death or abdication. However, if Aelianus was found to be responsible for Messalla's death, this guarantee would be null and void, and Aelianus would be subject to removal from the office of Caesar and execution. A ten-member regency committee was to be organized. Its purpose was to investigate the circumstances of the death of the Augustus if it deemed necessary, and to exercise all the powers and duties of the Augustus until such an investigation was complete. Five of the committee's ten members were to be appointed by Messalla, and the other five by Aelianus (although Messalla reserved the right to veto any of Aelianus' appointments).
After Aelianus died as a result of the Eastern Rebellion, Messalla chose to retain the Diarchy and actually use it as a means of ensuring orderly imperial succession. He chose Maximian as the new Caesar. Several months later, Messalla and Maximian signed the Second Treaty of Thessalonica. The second treaty modified the Diarchy in several ways:
- The province of Asia was broken up into the new provinces of Ionia, Caria, and Phrygia; with Caria and Phrygia being placed in the Dominium Caesaris.
- The share of the military forces over which Messalla would have control inside the Dominium Caesaris was reduced from 40% to 25%.
- Laws made by Messalla would only be binding within the Dominium Caesaris with the approval of at least one fifth of the provincial governors therein. 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.
Rule with Aelianus
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 Disbandment 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. Overtime, Senator Supremus would replace Augustus as the most commonly used title for the senior co-emperor.
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.
Map of the Roman Empire and the surrounding areas immediately after the Osrinian War 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.
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.
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 and signed the Second Treaty of Thessalonica.
Rule with Maximian
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 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 proposed 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. Messalla did adopt many of Diocles' proposals between 295 and 297.
Around the same time that Diocles was working on his civil service reform plan, he was also preparing to submit a plan to reform the currency to Messalla. Under this plan, the denarius (and coins based on the denarius, such as the antoninianus) would be replaced with five new coins: a gold coin called the solidus, a silver coin called the argenteus (worth 0.1 solidi), a bronze coin named the follis (worth 0.2 argentei), a copper coin called the radiatus (worth 0.1 follii), and a smaller copper coin called the laureatus (worth 0.25 radiati). There would also be a division of authority to mint coins: authority to mint solidi would be reserved solely to the Supreme Senator; both the Supreme Senator and the Caesar would be able to order the production of argentei; follis coins could be minted on the authority of praetorian prefects, and the copper coins could be issued by provincial governors.
The plan was accepted by Messalla in 293. Within a year, the new coins began to go into circulation.
Starting in 301, Roman Emperor Messalla began a project to build trade and diplomatic relations with tribes in northern Arabia. His hope was to eventually gain at least one ally for Rome to counterbalance Osroene.
Roman Reconquest of Cappadocia
After the Great Roman Civil War ended, Messalla ordered all Roman military units to withdraw from the breakaway provinces of Cappadocia and Osroene. Messalla deemed it best to begin the process of rebuilding the Roman economy before attempting to retake either province. Messalla had intended to invade Cappadocia within two years of retaking Osroene; but after Rome's defeat in the Osrinian War and the resulting economic setback and civil disorder in the eastern provinces, Messalla put the plans to invade Cappadocia on hold.
Several times during the early 290s, Messalla and Maximian both attempted to persuade the governor of Cappadocia to voluntarily rejoin the Roman Empire. Their efforts were totally unsuccessful. Neither the governor nor the people had any interest in rejoining. It remained unclear whether the political stability that Messalla had worked to build would last, and the Roman economy was only barely beginning to recover. Also, the governor did not want to see Cappadocia dragged into a war between Rome and another state, and he especially did not want Cappadocia to suffer the consequences of Rome being defeated in any such conflict. From the Cappadocian governor's point of view, Rome simply had nothing to offer Cappadocia.
After it became clear to Messalla and Maximian that Cappadocia would not rejoin the empire willingly, they began preparing to invade the province. One thing this involved was rebuilding the Roman army. Fifteen years after the civil war, the Roman army still only had around 200,000 soldiers. Messalla and Maximian agreed that it would take a force of around 35,000 — a significant portion of the army — to overwhelm Cappadocia's defenses and then suppress any rebellions. In order to recruit new soldiers, the two emperors made various promises in exchange for service in the army, including land and political power in Cappadocia, and generous salaries. Also, Maximian and his praetorian prefects and governors began generating anti-Cappadocian propaganda. Yet none of these efforts were very successful: between 293 and 298, the size of the Roman army increased by only seven thousand.
In 298, Messalla made two changes to the new currency system. One was that henceforward, solidus coins would be minted only to pay soldiers. The other was that a new silver coin worth two argentei, called a siliqua, would be introduced, and it would be minted only to pay soldiers. At the same time, production of normal argentei was to be reduced by a moderate degree. This produced powerful financial incentives for men in their late teens and their twenties to enlist in the army. The change in the coinage policy resulted in 30,000 men joining the Roman army between 298 and 304. In 304, Messalla, Maximian, and several prominent generals agreed that the time was right to invade Cappadocia.
The invasion began in May 304, with 40,000 Roman soldiers participating. Messalla opted for a two-front invasion. 25,000 of the participating men would invade from the southwest, and the remaining 15,000 would stage a naval invasion from the north. Both groups were able to break through the Cappadocian defenses. After winning the initial battles, the Romans steadily gained territory. In October, the governor of Cappadocia surrendered and recognized Messalla's authority.
After Rome retook Cappadocia, the northern part of the province was given to the province of Pontus, and the eastern half was made into a separate province called Armenia Minor. The provinces were added to the Dominium Caesaris. The governor of Cappadocia and most of his important civil and military officials were allowed to retire.
Growth of Christianity In the Roman Empire
On the eve of the Gallic War for Independence, Christians made up around ten percent of the population of the Roman Empire. By the end of the third century, Christians accounted for around fifteen percent of the Roman population. Existing churches grew, and new churches were organized in cities where Christianity had previously lacked any presence. Traditionally, Christians had been concentrated in urban areas; but during the late third century, Christianity began to spread to smaller villages (albeit mainly those near cities).
The primary reason for this unprecedented growth of Christianity was that Christianity was seen as a source of comfort for people who had lost everything in the devastation caused by the Gallic War for Independence and the Great Roman Civil War, as well as those who had their possessions confiscated as a result of the Osrinian War. Similarly, the civil war and the slow recovery left many people disillusioned with the empire's culture and political system, and many people saw in Christianity an alternative to a system that they believed had totally failed. Another reason was that during the Great Roman Civil War, the contenders for the emperorship and the provincial governors focused primarily on military matters and almost completely neglected to organize and preside over pagan ceremonies (though Messalla and his Caesars and governors resumed this responsibility after the war); so for many converts, Christianity filled this religious void.
State Reaction to the Growth of Christianity
The dramatic growth of Christianity did not go unnoticed by the state. During the early 290s, several provincial governors began informing the emperors of declining attendance at pagan ceremonies. The trend concerned Diocles, who was a very conservative pagan.
Starting in 293, Diocles began writing letters to the emperors urging them to address the trend, arguing that the growth of Christianity meant the abandonment of the values that had in the past made the Roman Empire great. For a time, neither emperor agreed to enact anti-Christian policies, but did not explicitly forbid Diocles from acting on his own. In 294, Diocles began purging Christians from the army and bureaucracy within the praetorian prefecture of Haemus.
In 297, the governor of the province of Sicily, who had converted to Christianity two years before, began refusing to organize or host pagan ceremonies, which had long been one of the roles of provincial governors. This prompted Messalla to issue an edict affirming that governors, praetorian prefects, and the Caesar were the chief priests of the Roman state religion within their respective jurisdictions, and that those offices could not be held by anyone who would not fulfill the religious responsibilities thereof. At Diocles' urging, Maximian went a step further and issued a decree that those who did not worship the Roman deities could not serve as generals or duces in the army. During the few years that followed, several governors and one praetorian prefect besides Diocles carried out total purges of Christians from the army and civil offices. Then in 305, Messalla issued a law banning the proselytization of Christianity. Also during the 300s, several governors and praetorian prefects reduced Christians to second-class citizens.
Third Gallo-Roman War
On February 24, 305, the First Gallic Civil War began after months of tension between the Gallic Empire's Senate and First Citizen, Carausius. In September 305, Messalla decided to exploit the fact that the Gallic Empire was in a state of civil war. Rather than attack the Gallic Empire itself, Messalla decided to invade Gaul's allies, the four Germanic states in Pannonia and Noricum. The Roman invasion of Pannonia and Noricum began on September 22, 305. Messalla sent a large invasion force to the area, and the Pannonian and Norican states were caught off-guard. Because of this, the Romans were able to conquer all of Suevia by October 18 and a third of Marcomannia by the end of October.
In November 305, Arpagius, who had prevailed over Carausius in the Gallic civil war and become the new First Citizen, sent troops to Pannonia and Noricum to help fight off the invasion. He also sent troops to invade Corsica and Mauritania Tingitana. The war lasted until September 4, 307. When it was over, the Roman Empire had managed to retake the part of Pannonia and Noricum south of the Savus (OTL Sava) River, while the Gallic Empire had annexed Mauritania Tingitana.
The African Rebellion
For several years before the Third Gallo-Roman War, discontent with Messalla had started to appear in the African provinces. The people of the African provinces (especially Numidia and the Mauritanian provinces) were beginning to believe that Messalla had neglected them relative to the rest of the empire. After the war with Gaul, the dissatisfaction with Messalla grew rapidly in northwest Africa.
By March 308, riots targeting local Roman officials were happening in many cities in northwest Africa, and militias were beginning to form. During June 308, militias seized control of three cities in Mauritania Caesariensis and one city in Numidia. Some army units joined up with the militias, while others tried to crush the rebellion. On June 13, 308, Gaius Annius Anullinus, the governor of Numidia, declared himself Supreme Senator (senior co-emperor) and his son Caesar (junior co-emperor). After this, several legions quickly turned against Messalla.
Anullinus promptly sent two legions and three auxiliary units to invade Rome. These legions left Africa on June 28 and arrived in central Italy on July 10. The invasion of Rome took place on July 13. There was only one legion protecting the city, and with that legion outnumbered and caught off-guard, the city quickly fell to Anullinus' forces. Messalla managed to escape to Spoletum (OTL Spoleto). From there, he summoned troops to Italy, informed Maximian of his situation, and ordered generals loyal to him in Africa to invade Numidia. The invasion of Numidia began on August 12. On August 16, Messalla led a campaign to retake Rome. By August 17, Anullinus' forces had been driven out of Rome, and pro-Messalla forces were closing in on Cirta (OTL Constantine), the capital of Numidia. On August 20, a legion in Mauritania Sitifensis that had remained loyal to Messalla seized control of Sitifis (OTL Sétif), the provincial capital. By then, most of the pro-Anullinus forces in Numidia had capitulated. On August 21, pro-Messalla forces took Cirta and killed both Anullinus and his son.
Death and succession
Messalla was injured in the battle to retake Rome from Anullinus. The wound was treated, but it became infected. Messalla died from the infection on August 24, 308. The local officials quickly sent the news of Messalla's death to Maximian, who was in Thessalonica. Maximian received the news on October 10. Maximian's first act as Supreme Senator was to make his son Maxentius the new Caesar of the Dominium Caesaris. Maximian left Thessalonica for Rome on October 31, and he arrived on December 17.