The Gallic War for Independence was a war fought between the Roman Empire and the de facto independent Gallic Empire between 275 and 277. Initially, the war was just between these two parties, but it later expanded, with the Alamanni, Suevi, Marcomanni, and Quadi entering the war on the side of the Gallic Empire.
BackgroundThe chain of events that led to the war began in 260, when Postumus rebelled against Roman Emperor Gallienus and declared himself Emperor. In the immediate aftermath of his seizure of power, Postumus was recognized as Emperor in the Gallic, Spanish and Britannian provinces. Instead of actively attempting to gain control over the rest of the Roman Empire, however, Postumus was content with administering the provinces that were loyal to him. He proved to be a good ruler: the provinces that recognized him enjoyed internal stability and prosperity that had been unknown for decades.
The Roman Empire continued to be plagued by civil war, external invasions, and hyperinflation of the currency. Gallienus reigned until 268, when he was murdered by his own senior staff. He made several attempts to retake western Europe, but none of them were successful. After Gallienus died, Claudius II reigned for two years. He did not recognize Postumus, but his priority was fighting off a massive Gothic invasion in the Balkans and Aegean islands. After Claudius II died, his brother Quintillus reigned briefly, but then died and was succeeded by Aurelian.
Aurelian demonstrated that he was an effective ruler during the first few years of his rule. He fought off Germanic invasions, reconquered the breakaway Palmyrene Empire, actively combatted corruption, and improved the coinage. He did not recognize the legitimacy of Postumus' rule, and he spent much of 274 preparing to go to war with Postumus.
Aurelian began his attack in early March 275. Unlike Aureolus and Gallienus, who had only tried to invade by land from the east, Aurelian launched two naval invasions: one, led personally by him, would sail from Corsica to Narbonensis; and the other one, led by a reliable general named Aurelius Marcellinus, would sail from Mauritania Tingitana to Baetica. Aurelian also had another general under his command named Julius Placidianus lead a land invasion. At first, Aurelian's forces were successful on two of the three fronts. Half of the units consisted exclusively of cavalry, and were therefore more mobile than traditional units, which consisted of a mix of cavalry and infantry. They took large swathes of land in Gaul and Spain.
By the middle of May, however, progress had begun to stall for Aurelian's forces. The land invasion had proven to be a total failure. Postumus had built up defenses in Raetia and Transpadana to a greater extent than Aurelian's spies has estimated. Placidianus also made the mistake of choosing to bypass the areas where troops loyal to Postumus were most heavily concentrated. His hope was for them to rush through Transpadana and begin seizing territory after reaching the minor Alpine princes. Instead, those units found themselves trapped. Approximately half of the soldiers fighting for Aurelian were killed in a fierce battle. The majority of the survivors chose to go deeper into enemy territory. Meanwhile, Postumus and his generals had had time to organize their forces to counter the attacks in Gaul and Spain. Postumus had been creating cavalry-only units since 272, and he ordered his generals to reorganize some of their units accordingly. These units proved effective at countering Aurelian's units several times during late April. Aurelian had also underestimated the loyalty of the masses to Postumus. Under Postumus, the people had enjoyed fifteen years of uninterrupted stability and prosperity; whereas the rest of the Roman world had continued to suffer chaos for years. The majority of the people believed that they owed Postumus everything and owed Aurelian nothing. Since the invasions began, many fighting-age civilians in Gaul, Spain, and Britannia had enlisted in the army under Postumus' control. Right before the invasion, the military forces loyal to Postumus had about 60,000 soldiers; but that number increased by 3000 by the middle of May, and would increase further throughout the remainder of the year.
The Invasion of Italy
In late May, Postumus planned an invasion of Italy. One of his generals, Laelianus, was to lead a large naval force from southwestern Gaul to central Italy. Meanwhile, another general, Victorinus, would lead a land campaign south from Mediolanum. The plan was for both groups to converge at Rome and sack it. Also, there was a third army loyal to Postumus that had gradually sneaked into southern Italy, a few men at a time, between 271 and 273. Postumus had sent in this "sleeper army" so that he would have troops already in Italy should he ever deem any campaign in the Italian peninsula necessary. This sleeper army, commanded by Julius Saturninus, had maintained contact with Postumus' empire, and now Postumus decided it was time for them to act: their mission was to wreak havoc in southern Italy to make it so that Aurelian's forces could not be concentrated in northern and central Italy.
A group of four ships set sail from southwestern Gaul to southern Italy in the middle of June. Their mission was to provide instructions to the sleeper army. A few days later, Laelianus' forces set sail for central Italy. Three days after that, re-inforcements summoned by Aurelian arrived in southern Gaul.
The instructions to the sleeper army arrived in early July, and the group was fully assembled within a week. On July 17, they began to attack cities and towns in southern Italy. The march from Mediolanum to Rome began on July 18, and the naval invaders from southwestern Gaul landed on July 22. Laelianus' forces reached Rome by July 24 and began laying a siege to Rome. Victorinus' troops joined them on August 3. The invading forces could not simply enter the city because Aurelian had recently had a wall built around it. The invaders began digging siege tunnels on July 26. Aurelian learned of trouble in Italy by August 4. By August 19, two tunnels had been completed and the invaders poured into Rome.
The invasion of Italy exceeded Postumus' expectations. Postumus correctly anticipated that the invasion would make it necessary for Aurelian to send some of his troops back. He also knew that the sack of Rome would serve as a severe embarrassment to Aurelian: the city of Rome had not fallen to invaders since 387 BC (and almost symbolically, the last time Rome had been successfully invaded, it was by a Gallic tribe). Moreover, by the middle of September, word had reached both Postumus and Aurelian that the Senate had evacuated Rome on August 27. (Forcing the Senate to evacuate Rome was not part of Postumus' plan, but was a goal that the generals leading the invasion had agreed upon several days before the sack began.)
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 troops led by Laelianus and Victorinus made it to Raetia by late November, albeit with heavy losses. The sleeper army led by Saturnius was far less fortunate. The sleeper army had tried to make its way to a coastal town, sail to northern Italy, and then march home to Raetia. Before they arrived at their destination, troops under the command of Marcus Aurelius Probus intercepted them on September 26 and killed the majority of them, including Saturnius. The survivors did make it to the coast, only to find re-inforcements from Dalmatia and Epirus waiting. Most of the survivors realized that their situation was hopeless at that point and surrendered.
After Aurelian learned of the details of the sack of Rome, he sent half of the re-inforcements that had come to him in June to Italy to deal with the invaders. He also ordered Aurelius Marcellinus to send half his forces to Italy, even if it meant having to pull out of some areas that he had already secured. In light of the invasion of Italy, Aurelian's strategy was to neutralize the invaders of Italy and at the same time get to Colonia Agrippina as quickly as possible. Then, after doing those two things, he could devote as much manpower, money, time, and resources as he needed to restoring Roman authority over Gaul, Spain, and Britannia. Postumus had expected that Aurelian would try to take Colonia Agrippina as soon as possible, so he had already increased the defenses near the city.
The Germanic Invasion
Back during late April, Postumus had sent envoys to the Alamanni, Suevi, Marcomanni, and Quadi. 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 leaders of the Suevi declined the offer, but the leaders of the other three tribes accepted, on the condition that Postumus develop and execute a workable plan for his own forces to invade another area under Aurelian's control.
In Postumus' dominion, the alliance was generally accepted among both the people and military. He had garnered support for the alliance among the people and military of his empire by presenting it as a way to weaken the Roman Empire and a way to give the Alamanni an incentive not to invade the Rhine frontier. Not everyone approved of the alliance, though. Several Senators and generals predicted that the alliance would force Postumus and any successor of his to actively aid the tribes that he had made the alliance with, whereas Postumus assumed that he would not find himself having to aid his allies anytime in the near future.
In the middle of September, the leaders of the three tribes that had conditionally agreed to the alliance informed Postumus that they would invade Pannonia and Noricum, due to the success of the invasion of Italy. The allied tribes began their invasion in late October. Aurelian's empire was caught off-guard, so the participating tribes managed to take a fifth of both Pannonia and Noricum within three weeks. After this, the local Roman generals were able to slow the invaders' progress. News of this did not take long to spread, and the Vandals and the Gepids opted to take advantage of the situation: by late November, they had crossed the Danube and begun to invade the Balkans.
Aurelian Begins to Lose Support
Prior to his war against Postumus, Aurelian had reconquered the Palmyrene Empire, actively combatted corruption, and improved the coinage; and for this he had steadily gained popularity. The sack of Rome — and the invasion of Italy in general — was a severe blow to his popularity. The fact that it was mainly forces already stationed in Italy and re-inforcements from Dalmatia and Epirus who confronted the invaders did not help Aurelian. Probus declared himself Emperor on October 4; stating that his leadership in dealing with the invaders had proved him to be truly deserving of the purple, and that the course of the war had proved Aurelian unworthy. Just two days later, the governor of Macedonia, Faltonius Pinianus, who had not learned of the announcement yet, also declared himself Emperor. The initial success of the Germanic invasion was a second blow for Aurelian. It also gave Pinianus a chance to prove his worthiness of the purple. He made fairly good use of that opportunity by slowing down the progress of the Germanic invaders.
A more interesting development was happening in Rome. For a over a month after the sack ended, no outside authority had a significant presence in the city, as the armies were still having to fight off the invaders from Gaul. Also, most of the aristocracy and local officials had either been killed or fled the city with the Senate. This meant that it was up to the masses to restore order and begin the difficult process of rebuilding the city. Several factions sought to fill the power vacuum. Most of these factions offered rule by a single individual or a small group in the short run and a transfer of authority to whoever or whatever ruled the rest of the empire in the long run, a couple of factions aspired to eventually take control of the entire empire, and then there was one faction that intended to establish a new Roman Republic. By the middle of October, it was clear that the plurality of the residents of Rome had thrown their support behind the Republicans. On October 11, the free men who supported the Republican faction elected one hundred men to a new Senate. This new Senate assembled the next day, whereupon they proclaimed the Second Roman Republic and appointed two Consuls. A relatively small group of soldiers affiliated with Probus came to Rome on October 17 in order to integrate Rome into Probus' regime, only to be fought off by a militia that had been organized in late September.
The Downfall of Aurelian
Meanwhile, Aurelian's campaign in Gaul was progressing slowly. Ever since the war began, almost ten thousand Gallic, Spanish and Britannian civilians had volunteered to fight for Postumus, and the effects this swell in the size of Postumus' military were clear. Postumus had more troops to defend Colonia Agrippina with. Meanwhile, Aurelian's soldiers and officers had steadily become dissatisfied since they had heard of the attacks in Italy.
The last straw came toward the end of 275. A large number of Spanish and Britannian units had quietly made their way to southern Spain during October. When they arrived, they began coordinating with local resistance cells that had been created during the spring and summer. The plan was for the outside forces to invade the areas controlled by Aurelian's forces on four fronts, two land and two naval, while the locals would stage uprisings in towns and cities near the locations of the invasions as well as several major cities in the interior of the occupied territory. All parties were to begin well before dawn on November 24. The plan was largely successful. The external attack on the eastern land front found itself bogged down, and some of the internal uprisings were quelled, but Aurelian's forces had lost much of the territory in Spain that they had still controlled within just a week. By the middle of December, forces loyal to Postumus had retaken all of Spain.
Aurelian's senior staff in Gaul had already been considering whether to kill him and set up a new Emperor. As soon as they learned that the forces in Spain were rapidly losing, they decided that they could no longer tolerate Aurelian. They also decided that he deserved worse than to simply be assassinated. On December 27, 275, while Aurelian was sleeping, soldiers loyal to Aurelian's senior staff overwhelmed Aurelian's bodyguards, entered his tent, broke all four of his limbs, and then dragged him into a cage. At dawn, Aurelian was presented to his forces, at which point one of his generals, named Julius Asclepiodotus, declared Aurelian deposed and declared himself the new Roman Emperor. This third usurper declared that his first act would be to pull out of Gaul.
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.
The Gallic Invasion of Noricum
By the middle of December 275, it was clear that the Alamanni, Marcomanni, and Quadi were getting nowhere. Victorinus, who had remained in Raetia since he returned from Italy, asked Postumus to allow him to aid the Alamanni by leading a campaign into Noricum. He received authorization from Postumus in early January. The invasion of Noricum began on January 9, 276.
Victorinus took his troops to Juvavum (OTL Salzburg), which the Alammani had been trying to capture since December. When the Gallic forces arrived, they attacked from the southwest. (The Alamanni had been trying to enter the city from the north, northwest, and west.) The combined strength of the Gallic and Alamannian armies was just enough to overpower the Roman forces. By January 26, Juvavum was under Alamannian control.
The Gallic and Alamannian forces began moving south from Juvavum on February 3. Their next destination was Teurnia (near OTL Spittal an der Drau). They conquered several small towns along the way. When they were about halfway to Teurnia, however, they encountered heavy resistance. Army units loyal to Asclepiodotus had come to Noricum. At this point, generals and provincial governors throughout the remainder of the Roman Empire were deciding which of the three claimants to the purple to support. Asclepiodotus was racing for the support of the governors of Noricum and Pannonia Superior against Pinianius, with whom the governor of Pannonia Inferior had already aligned. Asclepiodotus' forces were enough to completely halt the progress of the Gallo-Alammanian forces. On February 24, Victorinus sent a message to Postumus requesting additional troops.
Postumus decided to send more troops to Noricum on March 12. Unfortunately for him, this decision was not well received by the Gallic people. Most people knew that Victorinus and his army were in Noricum, but they had assumed the war with the Roman Empire was otherwise winding down. (For some people, even Victorinus' campaign was unacceptable.) They were hoping that the newly independent empire's resources to be devoted to rebuilding cities and towns that had been damaged in the war. Soldiers who had recently returned home from fighting the Romans had looked forward to at least a few years of peace. There were also people who had objected to the alliance from the beginning because they anticipated that it would force the Gallic Empire to actively prop up the allied tribes long after defeating the Roman invasion.
Postumus' decision to send more troops to Noricum had more support among the higher-ranking military officers and in the Gallic Senate, but that support was a reluctant support, and there were many in those circles who disapproved. On March 17, a moderately important Senator called for the deposition of Postumus. The proposal failed: on March 20, the majority of the Senators voted against considering possible replacements for Postumus; although the next day, the Senate did issue an official statement condemning Postumus' decision to send troops into Noricum.
Postumus' strategy was to deploy a vast number of troops from the interior regions of Gaul and Spain to southern and central Noricum, which Victorinus' army and the Germanic armies had yet to take. Postumus hoped that this would allow a large portion of Noricum to be taken before re-inforcements could arrive. He also decided to leave Colonia Agrippina and personally lead the invasion force. His reason for doing so was to show the Gallic troops that he believed enough in the necessity of the invasion of Noricum that he was willing to risk getting killed in battle or captured by the Romans, thereby encouraging them to fight with the same dedication that they had fought with a year before.
The Gallic re-inforcements began to move into Noricum on April 16. Postumus sent one third of them through the middle of the province, and ordered Tiberius Bonosus to lead them. He led the other two thirds to Teurnia, which was in southern Noricum. Both groups took several towns near the border, but then were slowed by troops affiliated with Asclepiodotus.
On May 7, spies in the army bound for Teurnia discovered a gap in the Roman lines. Postumus began sending soldiers through the gap on May 9, a few at a time. The plan was for a large part of the Gallic troops to gather behind the Roman lines and stage a flank attack. Unfortunately, the Romans realized what was going on on May 17, and attacked the detachment before it was ready. Now some of his men had noticed that a considerable number of Roman soldiers had shifted positions, so Postumus learned that his plan had been foiled fairly quickly. When he learned this, he decided he had no choice but to order a forward charge toward the side of the Roman camp that was closer to the Gallic detachment. As the Romans responded to this forward charge, Postumus sent the rest of his troops to attack the center. After pushing through the center of the Roman formation, the Gallic army began to branch off, forming corridors in the Roman position. Ultimately, the forces led by Postumus won; but the surviving Romans managed to escape and join up with the Roman units that were confronting the Gallic units commanded by Bonosus. This enabled the Romans to stall Bonosus' troops for a while.
On June 1, Postumus' forces reached Teurnia. Meanwhile, the Marcomanni broke a months-old stalemate with the Romans and began gaining ground on May 27.
Confrontation with the Second Roman Republic
Now while Asclepiodotus was attempting to gain ground in Noricum, another problem was emerging in the areas under his control.
After the Second Roman Republic was established, news of the event did not take long to spread. Rome had not been the only city where a power vacuum had resulted from from the Gallic invasion; and during November and December of 275, republican governments emerged in several other towns and cities that had been devastated during the Gallic invasion. Most of these towns aligned with Rome.
Asclepiodotus and Probus had each made a couple of attempts to take Rome and the other republican cities, but after those attempts failed, they both decided that taking Rome could wait. It did not seem like the republican movement would spread very far and thus did not pose a threat to either of them. Both generals had left the Republic alone since January 276. In April, however, the situation began to change. Republican revolutions were beginning to occur in the dominions of both generals. The majority of these uprisings were taking place in Sardinia and the Italian district of Etruria, which had been governed by Asclepiodotus. There were also revolutions occurring in Sicily, which had been controlled by Probus. In early June, both generals decided that the republican movement had to be crushed only three days apart from each other.
The majority of troops Asclepiodotus sent to confront the republics had to come from Mauritania, because Asclepiodotus wanted the soldiers stationed in northern Italy to be available to be sent into Noricum. This meant that there would be a considerable delay before Asclepiodotus could actually go to war with the republican states. Only the Sardinian Republic could be dealt with immediately: Asclepiodotus just sent in troops from Corsica and the parts of Sardinia still under his control. Probus did not have this problem, because at that point, he happened to not be actively fighting Gaul, Germanic tribes, or Pianius or Asclepiodotus.
On June 6, Probus launched a massive land invasion of the Second Roman Republic. His forces took much of the republic's territory within three weeks, including Rome itself. He also deployed forces to overrun the Sicilian Republic. Meanwhile, the Sardinian Republic fell to Asclepiodotus on June 18. Asclepiodotus also sent some troops to take Arretium (OTL Arezzo), which was located on the northern edge of the Second Roman Republic's territory, on June 21. Then on June 23 and 24, troops from Corsica and Sardinia carried out a two-day campaign to retake the Etrurian Islands (OTL Tuscan Archipelago).
An Unwanted Clash
On June 26, the troops that Asclepiodotus had summoned from Mauritania arrived in Italy. Now some of those units landed in areas that had already been taken by forces loyal to Probus. The commanders of some of the units that landed in Probus' territory ordered their troops to simply withdraw to Sardinia in order to avoid a confrontation with Probus' troops. In the towns of Lavinium (OTL Pomezia) and Ostia, however, fighting broke out between the forces loyal to Asclepiodotus and those loyal to Probus. Exactly what caused the fighting was unknown. Asclepiodotus' forces managed to take control of Lavinium but were driven out of Ostia.
A similar problem was developing further north in Italy during the last few days of June and the first few days of July. As the armies of the two generals closed in on the last remnants of the Second Roman Republic, they clashed with each other frequently, as both armies often arrived at the same places no more than a couple of days apart. There were several cases where the army of one general drove the army of the other out of a town that the latter had just captured.
Word of the Battles of Lavinium and Ostia took eight days to reach Asclepiodotus, who had made Florentium (OTL Florence) his temporary capital, and six days to reach Probus, whose headquarters was in Syracuse. Each general was worried about what the other would do. Neither wanted to actively fight each other while the Gallo-Germanic invasion was going on, but such a confrontation was beginning to seem inevitable.
In fact, the point of no return was crossed by the forces stationed in and around Lavinium before instructions from either general could arrive. On July 1, Probus' forces attempted to retake Lavinium. They managed to get close to the town center. The forces affiliated with Asclepiodotus managed to hold out long enough for the commander to request backup from Sardinia, and these re-inforcements arrived. Asclepiodotus' troops had regained control of Lavinium by July 5, and then began moving into the surrounding areas two days later.
Probus knew that a prolonged conflict with Asclepiodotus would prevent either of them from effectively confronting the Gallic and Germanic invaders in Pannonia and Noricum, so he chose to throw almost his full strength against Asclepiodotus' Italian territories in order to quickly dislodge Asclepiodotus from Italy. Thereafter, his plan was to lead a large and relatively united army into Noricum and the two Pannonian provinces. Now while Probus had more men at his disposal, he faced a disadvantage in that many of them had to be summoned from Africa Proconsularis, Cyrenaica and Crete, and Egypt. While all those units were en route to Italy, Asclepiodotus managed to wrest the central third of the peninsula from Probus without having to divert troops from Noricum (this was because of the troops that had been brought in from Mauritania earlier). The majority of the armies from outside Italy did not arrive until the middle of September. After these armies arrived, they began fighting to retake central Italy and take northern Italy for Probus. It seemed like the conflict between Asclepiodotus and Probus would be long and bloody.
The Downfall of Asclepiodotus
By October, Asclepiodotus was finding himself in an increasingly bad situation. During the summer, the Alamanni, Marcomanni, and Gauls had steadily advanced through Noricum: Asclepiodotus had only managed to slow them down. Because of his problems in Italy, he was unable to send re-inforcements into Noricum. The governor of Pannonia Superior sided with Pinianus in early September.
Asclepiodotus lost several key cities to Probus during the first half of October, including two in Sardinia and one in Corsica. After this, out of desperation, Asclepiodotus chose to redeploy all the troops under his command in Noricum to the Italian front. When the instructions to leave Noricum reached the units there, the response was mixed. Some followed the orders, but others refused to comply and declared allegience to either Probus or Pinianus. When Asclepiodotus learned of this, he knew that the situation in Italy was hopeless, and he left Florentium for Corsica on November 4. He hoped to at least secure Corsica, Sardinia, Numidia, and the Mauritanian provinces for himself immediately and prepare to take over the rest of the Roman Empire in the long run. But even this was not to be: on November 25, Asclepiodotus was murdered by his own bodyguards.
After the death of Asclepiodotus, Flavius Antiochianus declared himself Emperor. He was recognized as such in most of the areas where Asclepiodotus had been recognized. However, he only received limited recognition from the commanders stationed in Italy who had previously answered to Asclepiodotus: some of them had already defected to Probus.
The November Offensive
Meanwhile, the temporary decrease in the Roman military presence in Noricum allowed the Gauls, Alamanni, and Marcomanni to gain more ground. At the beginning of November, the alliance was still struggling to take the southwestern quarter of Noricum, and had failed to move very far beyond Vindobona (OTL Vienna) in Pannonia Superior. By the end of November, they had taken all of Noricum except for Flavia Solvia (near OTL Leibnitz). They had also made more modest gains in Pannonia Superior.
The progress of the alliance had clearly come to another stop by early December, however. The allies had reached territories controlled by Pinianus. Pinianus had been firmly in control of the Balkans and Anatolia for a year, and he had avoided active conflict with the other contenders for the Roman throne.
Expansion of the Gallo-Germanic Alliance
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.
On December 18, 276, Postumus met with the Alamanni, Marcomanni, and Quadi leaders, and also Victorinus and Bonosus. They discussed the situation and how they could withstand the armies of Probus and Pinianus. Postumus said that he thought it would be a good idea to again reach out to the Suevi. The Alamanni agreed, but the Marcomanni and Quadi were not as supportive of the idea. The reason for each tribe's position had to do with apportionment of territory: the entire area that the Alamanni were promised (western Noricum) had been taken, so the Alamanni saw little chance that they would have to cede territory to the Suevi; but the Marcomanni and Quadi anticipated that they would have to forego parts of Pannonia that they had been promised. The Marcomanni and Quadi leadership did recognize that the alliance needed help, so they told Postumus that they were willing to renegotiate planned boundaries in Pannonia to accommodate the Suevi. The Gallic, Marcomanni, and Quadi leadership discussed new borders over the next three days, and reached an agreement on December 21. Representatives from Gaul, the Alamanni, and the Quadi were sent to the Suevi the same day.
On January 7, 277, the messengers from the alliance returned from the Suevi realm and announced that the Suevi leaders were considering joining the alliance and wished to meet with the allied leadership. The allies agreed, and a conference began on January 20. Initially, negotiations were difficult. The Suevi had a different proposal regarding how Pannonia should be divided. The Suevi asked for over half of Pannonia, as the Marcomanni had already won eastern Noricum and the Quadi were less numerous than the Suevi. Eventually, a compromise was reached. The Suevi were promised about a third of Pannonia. To address the Suevi's concerns that the Suevi were not being offered a sufficient share, one detail of the compromise was that the Suevi would have the "option" of expanding into Dalmatia, although the compromise did not explicitly call for the other parties to assist the Suevi in doing so.
Meanwhile, Roman armies loyal to Probus had finally gained undisputed control of northern Italy, and began to move into Noricum during the last week of December 276. At first, Gallic and Alamannian troops were able to keep the Romans away, but the Romans broke through the allied lines on January 18, 277 and began advancing toward Teurnia. More Romans came, and the Romans won several towns in southwestern Noricum. Teurnia fell to Probus' forces on January 26, the same day that the Suevi agreed to enter the war.
In eastern Noricum, the alliance managed to take Flavia Solvia on January 29. They also took Scarbantia (OTL Sopron) in Pannonia Superior on February 5. Troops from northern Noricum arrived in the southwestern part of the province in the second week of February. Because of the greater military presence in southwestern Noricum, the advance by Probus' troops was halted and part of Teurnia was retaken.
On February 27, however, the forces loyal to Pinianus invaded Flavia Solvia, and had fully retaken it by March 2. Pinianus had sent a massive number of units to the area. He intended for this force to create a corridor through the middle of Noricum after securing Flavia Solvia. For a while, it did work. Roman forces won several towns during March. Meanwhile, Probus' forces drove the alliance forces out of Teurnia again in early March.
By late March, however, Suevi units began to arrive in Noricum. After the Suevi joined the fight, the allied forces able to stall the offensives of both Probus and Pinianus.
The End of the War
The Suevi were one of the larger Germanic tribes, so they were able to provide many soldiers to the alliance. Within a month of the Suevi entry into the war, the gains made by Probus and Pinianus had been completely reversed. Probus' forces were driven out of Teurnia by April 12, and out of Noricum completely by April 21. The alliance retook Flavia Solvia on April 18. Allied forces also began to gain new ground in late April. By the end of the month, they had reached the Arrabo River (OTL Rába River).
During May and early June, neither the alliance nor the Romans made much progress. A new development occurred 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. Thereafter, the army split into two groups. Three fifths headed toward Mursa (OTL Osijek), which was on the Drava River; and the other two-fifths headed south toward Colonia Aurelia Cibalae (OTL Vinkovci), which was about twenty miles south of Mursa. Both cities were attacked on June 11. Mursa fell on June 14, and Colonia Aurelia Cibalae fell on the June 16.
By late June, the Gallo-Germanic forces reached Sopianae (OTL Pécs). Re-inforcements were sent to the city from the interior of Pannonia Superior, which was at that point still controlled by Pinianus. The eastern Gallo-Germanic army was driven away from Sopianae after a seven-day battle; but on July 3, the western forces managed to break through the Roman lines and take Poetovio (OTL Ptuj) three days later, and then easily took much of the surrounding area over the next two weeks because of the decreased military presence. The eastern invaders made a second attempt at Sopianae later in July and took it on July 19.
News of the Roman defeats in Pannonia spread through the Balkans and Anatolia, the areas that comprised the core of Pinianus' territory. By late July, the generals, soldiers, and civil authorities in these peninsulas were beginning to lose faith in Pinianus. Finally, on August 4, a general stationed in Moesia Inferior named Lucius Flavius Aper rebelled against Pinianus. The governors of Moesia Inferior, Thrace, and Bithnia and Pontus quickly joined him. Troops that could have been sent to Pannonia were instead sent eastward to put down the rebellion.
Probus was not faring much better. His forces had gotten nowhere since April. Discontent with him was growing. Meanwhile, Antiochianus, the successor to Asclepiodotus, was acting as Roman Emperor in Corsica, Sardinia, Numidia, and the Mauritanian provinces. Probus had seized northern Italy from Antiochianus by December 276, but had then left Antiochianus alone in order to concentrate on Noricum. On August 10, a general who had defected from Asclepiodotus to Probus declared allegience to Antiochianus. Five days later, the governor of Africa Proconsularis also defected to Antiochianus.
As the Romans turned against each other, the Gallo-Germanic alliance found it easier to gain ground in Pannonia. The conflict between Pinianus and Aper was not resolved quickly, so re-inforcements were not sent. Similarly, Probus had turned his attention to dislodging generals who had defected to Antiochianus. The alliance's last major challenge came in October. By that time, only Sirmium (OTL Sremska Mitrovica) and Bassianae remained under Roman control. Many troops were stationed in the vicinity of these two cities, so it took the allies sixteen days to take both of them. 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.