Great Roman Civil War (Gaul Rising)

The Great Roman Civil War was the longest and most destructive civil war in the history of the Roman Empire. This war was the climax of a long period of political instability in the Roman Empire. The causes of the war were the near-simultaneous but separate challenges to the rule of Emperor Aurelian by Probus and Pinianus, the emergence of Julius Asclepiodotus as a third contender for the Roman throne after his successful mutiny against Aurelian, and a clash between forces loyal to Probus and forces loyal to Asclepiodotus that quickly got out of control.

The Long Crisis of the Roman Empire
A turning point in Roman history occurred in 235 AD. That year, Alexander Severus was murdered by his own troops. His troops then proclaimed a general named Maximinus Thrax the new Emperor. Thrax was not liked by the Senate; so when Gordian, the governor of Africa Proconsularis, rebelled, the Senate was eager to back him. The rebellion failed, and Thrax prepared to march on Rome to punish the Senate. Ultimately, Thrax's invasion of Rome failed, so he met the same fate as his predecessor: murder by dissatisfied troops under his command.

Maximinus Thrax's reign set the tone for the next several decades. There had never been any formal procedure for imperial succession; and the rise of Thrax was seen by many generals and provincial governors as indicating that rebelling against the current Emperor was a perfectly acceptable means of becoming Emperor, and the message that was widely taken from downfall of Thrax was that any failure by the current Emperor or any claimant to the throne could be used as a pretext for rebellion. The following cycle dominated the next four decades: a general would gain broad recognition as Emperor, immediately have to contend a rebellion or external invasion, and in many cases be killed by his own troops, who would then align themselves with a new contender for the throne.

There were two problems that developed as a result of the political instability. One was that as Roman generals turned on each other, they had less manpower and resources to devote to defending the borders against increasingly dangerous Germanic tribes. Germanic invaders frequently raided cities throughout the empire. Another consequence of the political instability was a debasement of the Roman currency, resulting in hyperinflation: whenever a general would declare himself Emperor, he would promptly order the minting of a large supply of coins to pay his troops with.

By 260, the local authorities were beginning to take up the primary responsibility for defending their jurisdictions against external invaders. In the Syrian provinces, a general named Lucius Septimius Odaenathus was nominally loyal to Emperor Gallienus, but was in fact highly autonomous. (He died in 267, after which his wife, Zenobia, took over his realm and openly rebelled against the central government.) In western Europe, Postumus declared himself Emperor, thereby effectively founding the Gallic Empire (though he would not officially declare his dominion independent from Rome until 276).

The Gallic War for Independence
After Postumus rebelled, Gallienus made two attempts to regain control over western Europe. Both attempts failed. Gallienus' successor, Claudius II, did not recognize Postumus, but he could not challenge Postumus as he had to fight off a massive Germanic invasion in the Balkans and then died shortly thereafter. Similarly, his brother Quintillus only reigned a few months before dying, and thus did not have a chance to confront Postumus either. After Quintillus died, Aurelian succeeded him. Aurelian reconquered Zenobia's Palmyrene Empire from 272 to 273, and then he launched an invasion of the Gallic Empire in 275.

Aurelian's invasion did not go well. Aurelian underestimated the loyalty of the locals to Postumus: many civilians had enlisted in Postumus' army to fight for him, and this dramatically slowed the campaign down. Then Postumus launched a counterinvasion into Italy, which is remembered most for a brutal attack on the city of Rome and more generally for the use of scorched earth tactics in many parts of Italy. He also persuaded the Alamanni, Marcomanni, and Quadi to invade Pannonia and Noricum. The invasions of Aurelian's territories prevented Aurelian from sending reinforcements to Postumus' realm.

The slow progress of the invasion of western Europe, the counterinvasion of Italy, and the Germanic invasions of Pannonia and Noricum caused Aurelian to fall out of favor with the people and military of the Roman Empire. By the end of 275, Aurelian had been deposed, and Probus, Asclepiodotus, and Pinianus had claimed the Roman throne. Initially, each of the three candidates sought to avoid fighting each other, as they were still at war with the Gallic Empire and the Germanic tribes that had allied with it. Then in early 276, a populist republican movement in central Italy began to pose a threat to both Probus and Asclepiodotus, and both generals simultaneously decided to conquer the areas under republican control. Probus was able to take many of the republican cities and towns quickly, because he simply sent troops to central Italy from Sicily and southern Italy; whereas Asclepiodotus had to call in troops from Mauritania, who took several weeks to arrive. Many of the troops affiliated with Asclepiodotus ended up landing in cities and towns that Probus had already taken.

The Battles of Lavinium
The Great Roman Civil War is generally considered to have begun on June 26, 276, the date on which the Battles of Lavinium and Ostia began. On that day, troops that Asclepiodotus ordered in from Mauritania arrived in republican Italy. Some of those units landed in areas already taken by Probus. 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 in each town was unknown. The clashes resulted in Asclepiodotus' forces taking Lavinium and Probus' forces retaining Ostia.

After the Battles of Lavinium and Ostia, the commanders who had participated sent communiqués to Asclepiodotus and Probus informing them of the situation. Probus considered the possibility that the seizure of Lavinium was the result of a misunderstanding, so he ordered the troops stationed around Lavinium to try to resolve the situation peacefully. Similarly, Asclepiodotus hoped to avoid an active confrontation with Probus, so he ordered a full withdrawal from Lavinium. Unfortunately for both candidates, it took several days for the news of the Battles of Lavinium and Ostia to reach each of them, and another few days for their orders to get back to central Italy. This meant that the commanders in and around Lavinium on both sides were on their own for nearly two weeks. Asclepiodotus' commanders assumed that since Lavinium had been taken, he would want them to hold onto it; and Probus' commanders assumed that he would want Lavinium to be retaken as soon as possible. Thus, the Second Battle of Lavinium began on July 1, before either candidate even knew about the original incidents.

The Second Battle of Lavinium lasted until July 5. This battle resulted in Asclepiodotus' forces retaining the town. Probus' forces moved in on July 1. By the end of the day, it was clear to Ascleiodotus' local commander that help would be needed, so he sent for reinforcements from Sardinia. Probus' forces steadily advanced during the next two days. Then on July 4, the reinforcements from Sardinia came, and had driven Probus' forces out of Lavinium by the end of the following day.

June 276 – January 277
On July 7, 276, forces affiliated with Asclepiodotus began to move out of Lavinium to take the surrounding areas. Then on July 8, Probus' orders regarding the situation in Lavinium reached the local commanders. The commanders quickly sent out a reply explaining that Probus' orders were not relevant to the current situation, and that he had been forced into a war with Ascleiodotus. Similarly, when Asclepiodotus' orders reached the front lines on July 11, his commanders sent a reply telling him that it was too late. Probus and Asclepiodotus received their updates on July 13 and July 18, respectively.

Probus chose to throw almost his full strength against Asclepiodotus' Italian territories in order to quickly dislodge Asclepiodotus from Italy. There were more men stationed in the parts of the Roman Empire that recognized him as Emperor than there were in the areas loyal to Asclepiodotus; and unlike Asclepiodotus, Probus was not actively fighting the Gallo-Germanic alliance. On the other hand, Asclepiodotus had the benefit of already having a large number of troops in Corsica and Sardinia ready to fight, whereas Probus would have to summon forces from Africa Proconsularis, Cyrenaica and Crete, and Egypt.

Between the middle of July and early September, Asclepiodotus made excellent use of the close proximity of his forces to Italy. His forces took two swathes in central Italy: one starting from Lavinium, going through Praeneste and Corfinum, and terminating at the Adriatic Sea; and the other going up the segment of the Tiber River controlled by Probus. Asclepiodotus' army gained access to the Tiber after winning the Second Battle of Ostia on July 21 and the Battle of Rome six days later. By the middle of August, enough progress had been made on both corridors that Asclepiodotus began sending troops to take the areas in between them. Then on August 25, troops loyal to Ascleiodotus invaded Capua from Sardinia, thereby beginning the First Battle of Capua. Capua was heavily fortified at that point, so the naval invaders were not able to take the city until after reinforcements who had been making their way southward on land arrived, and even then only with difficulty. Capua finally fell to Asclepiodotus on September 6.

In early September, troops loyal to Probus began arriving in southern Italy from Africa Proconsularis. Their presence made it impossible for Asclepiodotus' forces to advance south of the Volturnus River (OTL Volturno River): Asclepiodotus' forces were fought off in the Battle of Beneventum (OTL Benevento) and the Battle of Cusae (OTL Cusa). Then on September 14, ships carrying soldiers from Egypt and Cyrenaica landed along the Italian Adriatic coast. Some of the soldiers landed in northern Italy, ready to seize it from Asclepiodotus; others landed in central Italy, not knowing that it had been brought under Asclepiodotus' control. Fierce battles ensued along the Adriatic coast. More troops came in from Probus' African territorries over the following few days. By the end of the month, Probus' forces had taken several towns and cities on the Adriatic coast, as well as Capua and Lavinium.

Asclepiodotus' situation continued to deteriorate during October. Since June, he had failed to do anything more than slow the advance of the Gallic, Alamannian, and Marcomannian armies. In northeastern and central Italy, he was continuing to lose territory to Probus. Forces affiliated with Probus also began attacking Corsica and Sardinia, and had managed to take one key city in the former and two in the latter by the middle of the month. Also during the first half of October, several lower-level commanders in Italy defected to Probus.

Out of desperation, Asclepiodotus ordered all the troops in Noricum under his command to go to Italy. He hoped to get Probus to leave him alone, and then intended to turn his attention back to Noricum. To many of the soldiers fighting in Noricum, even a temporary departure from the province was unacceptable. Some units followed the orders, but others refused to leave and defected to Probus or Pinianus. When Asclepiodotus learned that many of the troops in Noricum had defied his orders, he realized that the situation in Italy was hopeless. He left Florentium for Corsica on November 4. Units were continuing to defect, and one general had joined Probus too. Asclepiodotus ordered some of the troops that were still on his side to leave Italy. He hoped to at least secure Corsica, Sardinia, Numidia, and the Mauritanian provinces for himself in the short run. His plan was to focus on administering those provinces until the time seemed right for challenging whoever or whatever was ruling the rest of the Roman Empire. During November, his forces managed to retake the parts of Corsica and Sardinia that Probus had controlled. However, it was too late: during November, several officials who had remained ostensibly loyal to Asclepiodotus began plotting to kill him; and on November 25, he was killed.

After the death of Asclepiodotus, Flavius Antiochianus declared himself Emperor. He was recognized as such in Corsica, Sardinia, Numidia, and the Mauritanian provinces; but many of the commanders in Italy who had recognized Asclepiodotus as Emperor before October had already defected to Probus at that point, and there were too few commanders that recognized Antiochianus to effectively resist Probus. The last three Italian cities under Antiochianus' control fell to Probus' forces during the last week of December.

January – August 277
After Probus gained control of northern Italy, there was little fighting between Probus, Pinianus, or Antiochianus. During this time, Probus and Pinianus devoted most of their attention to fighting against the Gallic and Germanic invaders in Pannonia and Noricum, and Antiochianus focused on the internal affairs of his realm.

During the spring of 277, both Probus and Pinianus were able to retake parts of Noricum from the Gallo-Germanic alliance. These gains were reversed by late April, after the Suevi entered the war. Then in June and July, Pinianus suffered major defeats in Pannonia. As the news of these defeats spread throughout the Balkans and Anatolia, Pinianus began to lose support. Finally, Lucius Flavius Aper from Pinianus and declared himself Emperor on August 4. Then on August 10, a general under Probus defected to Antiochianus.

August 277 – January 280
Pinianus continued to fight the Gallo-Germanic alliance, but he was forced to redeploy troops from Pannonia in order to confront Aper. This ultimately resulted in the alliance taking the rest of Pannonia by the end of October 277. Probus had not been actively fighting the alliance since June 277.

After October 277, Pinianus turned his full attention to defeating his challenger. Aper had immediately been recognized in Moesia Inferior, Thrace, and Bithnia and Pontus, and also by several generals stationed elsewhere. In early September, he tried to take Thessalonica, which Pinianus had made his provisional capital. This effort ultimately failed: as soon as Pinianus had heard of the rebellion, he began sending large numbers of troops that were still loyal to him to Thessalonica and the surrounding area, and those forces were enough to hold off Aper's forces. For several months thereafter, neither Pinianus nor Aper made any gains over the other.