Shortly after the de facto secession of the Gallic Empire from the Roman Empire, Gallic Emperor Postumus set up a new Senate in Colonia Agrippina. At first, the Gallic Senate was identical to its Roman counterpart. During the 270s, Postumus began to believe that in order to maintain political stability in his empire, it was necessary for him and his successors to deal with the Senate as an equal, rather than make it a puppet. In accordance with this view, Postumus gave the Senate the power to depose and replace the emperor, choose the emperor's successor in the event of the emperor dying or abdicating without choosing his own successor, and the power to appoint the majority of the provincial governors.
The second Gallic Emperor, Victorinus, did not share Postumus' vision of genuine co-operation between the emperor and the Senate. Throughout his rule, he frequently removed senators who opposed his agenda from the Senate and replaced them with loyal allies of his. The first and most notable time he stuffed the Senate with his partisans was in 282, when the Senate was about to vote on a motion to depose him.
Victorinus died in 293 without naming a successor. Because Victorinus had not designated a successor, the responsibility of choosing the new First Citizen (which had become the official title of the Gallic Emperor) fell on the Senate. When the Senate was considering who to elect, one of the main issues that came up was the relationship between the Senate and the new First Citizen. Two factions emerged in the Senate. One, called the Postumians, wanted to re-instate Postumus' policy of co-operation between the emperor and the Senate; and the other, called the Princepists, were content with the Senate deferring the wishes of the emperor and the emperor using his authority over the Senate's membership to remove his opponents. The Postumians threw their support behind Tetricus, while the Princepists were divided between Laelianus, Bonosus, and Carausius. The Senate held the election on March 1, 294. Tetricus won the election by a narrow plurality vote, and he designated Carausius his successor.
Tetricus and his supporters promised that Carausius would succeed Tetricus only to win the votes of enough of Carausius' supporters. Tetricus would rather have chosen a Postumian for his successor, and Carausius did not share Tetricus' sympathy for the interests of the Senate. From the very beginning of his reign, Tetricus relegated not only Carausius but also his closest associates to administrative offices and military commands that were unimportant, and reserved important civil and military positions for Postumians. The idea was to make it so that if Carausius did indeed succeed Tetricus, he would lack meaningful leadership experience, and be heavily dependent on Postumians who had been groomed to exercise the real power.
The Assassination of Tetricus
By 304, Carausius had decided that the only way he could ever hope to rule without being a puppet of allies of Tetricus was by having Tetricus assassinated and seizing the throne by force. Now at this time, Carausius was governor of the province of Asturia (in northern Spain). On March 9, he sent a letter to a longtime friend of his named Sextus Aurelius Allectus. At that time, Allectus held a minor military command in Belgica (specifically, he was a centurion), so he was the closest person to Colonia Agrippina whom Carausius trusted. In the letter, Carausius promised that if Allectus were to participate in the assassination, he would be rewarded with an important role in the government under Carausius, and possibly even be chosen to succeed Carausius; assurred Allectus that if he declined to participate, it would not be held against him; and asked Allectus to tell him whether or not he was willing to oversee the assassination. Allectus received the letter on April 27; and on May 2, Allectus sent a reply in which he informed Carausius that he was willing to participate.
Planning the assassination was Allectus' responsibility, since he was much closer to Colonia Agrippina than Carausius. He had several friends and associates in Colonia Agrippina. Without revealing his intent to have the emperor murdered, he began asking those contacts about the people they knew and regularly dealt with. Specifically, he asked if any of them knew men who could be considered highly unscrupulous or men who were desperate to escape debt or poverty. He also sent a couple of men under his command to visit nearby prisons to learn about the people who being held there. He also noting which of the men in his unit stood out as particularly ambitious. Allectus' goal was to find several people who easily could be bribed into participating in the assassination.
Over the summer of 304, the details of the plan began to take shape. Several men would be trained in archery. Once Allectus was satisfied that their skills as archers were good enough, a date for the assassination would be selected. On that date, the assassins would hide near the building where the Senate met, and shoot as he was about to enter. Thereafter, the assassins would be hidden. Once Carausius had secured his authority over the Gallic Empire, the assassins would received whatever rewards they were promised.
At the same time that the plan was developing, however, the activities of Allectus aroused the suspicions of his immediate superior, the commander of the cohort that Allectus' unit was a part of. He noticed that men under Allectus' command would sometimes be absent. Also, the volume of mail to and from Allectus began to increase. At the same time, jailers in Belgica were beginning to wonder why Roman soldiers were wanting to learn everything they could about the current prisoners, as well as prisoners who had been released. In spite of this, there was nothing to clearly suggest that Allectus was involved in any conspiracy. Allectus had considered bribing the guards to release one or two prisoners, but he eventually chose not to do that, feeling that that would implicate him in the killing of the emperor.
On July 6, Carausius received Allectus' letter in which Allectus informed Carausius that he was willing to oversee the assassination of the emperor. After Carausius received and read the letter, he immediately began preparing to leave Lucus Asturum (OTL Llanera) for Colonia Agrippina, and he left on July 20.
The assassination of Tetricus took place on the morning of September 8, 304. On that day, Tetricus was on his way to the Senate building. Five men were hiding at different points near the entrance. Two were criminals who had previously served time in prison, one was a farmer who was deeply in debt, and two were low-ranking but ambitious soldiers in Allectus' unit. As Tetricus began to walk up the steps that led to the door, all five of the assassins shot arrows at him. Each assassin had dipped his arrows in poison. Three of the arrows hit Tetricus, and he fell to the ground. Each of the assassins shot a second arrow; and one of those arrows hit him, and three hit his bodyguards. Thereafter, all five of the assassins fled the scene. Tetricus and the two bodyguards of his who were shot died within minutes.
Conflict between Carausius and the Senate
Carausius arrived in Colonia Agrippina on September 18. By that time, word of Tetricus' death had begun to spread beyond the city, so nobody was surprised that Carausius knew what had happened by the time he arrived. Nevertheless, the mere fact that Carausius was in Colonia Agrippina so soon was widely recognized as strange: nobody had summoned him, he had obviously left Lucus Asturum long before Tetricus was killed, and he refused to explain to anyone why he was there. Suspicion that Carausius was involved in the murder quickly began to arise. In spite of this, Carausius immediately assumed the office of First Citizen.
By 304, over 100 of the 250 senators were Postumians. There were also many senators who were indifferent to the issue of the relationship between the Senate and the First Citizen, but believed that Carausius would not be a strong leader. Thus, the Senate was hostile to Carusius by default. At the same time, Carausius, as First Citizen, had the power to appoint or remove as many senators as he wished. In an effort to prevent Carausius from altering the Senate's membership, the majority of the Postumians agreed not to challenge him immediately. Several Postumian senators also met with Carausius in an effort to persuade him not to expand the size of the Senate. Those senators were able to convince Carausius to leave the membership of the Senate as it was until March 8, 305, in return for several concessions.
Having bought themselves several months, the Postumians quickly began working to garner enough votes to depose Carausius. They also began discussing who the replacement should be. There were several possible candidates, but the two most frequently considered were Aurelius Arpagius and Tetricus' son, known as Tetricus the Younger. Arpagius had led the campaign to conquer the province of Amasiga several years earlier, and Tetricus the Younger had held several important civil offices.
Several dozen senators also began investigating the death of Tetricus. At first, those senators only searched in and around Colonia Agrippina for people involved. However, none of the five assassins were in that area: both of the criminals had been quietly transported out of Germania Inferior after receiving pardons from Carausius, the farmer was from Belgica and had quickly returned home after the murder, and the soldiers in Allectus' unit likewise returned to where the unit was stationed. There had never been anybody else in Colonia Agrippina who was involved in the conspiracy (besides Carausius). The senators conducting investigations realized this by the middle of November, so they began reaching out to contacts who were further away from the capital for information. As it turned out, one such informant was a junior officer from the very cohort that Allectus was serving in (though not the same unit within that cohort). In late December 304, a letter was received from him saying that he had heard talk of unusual activity within Allectus' unit for several months, as well as rumors of two foot soldiers from Allectus' unit who seemed to have begun receiving a higher wage than what was normal for men of their rank.
As for Carausius, he went back on his promise to leave the membership of the Senate as it was. In December 304, he had two senators arrested on entirely fictitious charges, and arranged for the disappearance of another. Two of those three were from the faction that was concerned mainly with having a strong leader, and one was a Postumian; and none of those three were considered important. All three were replaced with Princepists. At the same time, he also bribed, threatened, and blackmailed five other senators — all from the strong leadership faction — into supporting his agenda and opposing anything that would threaten his power. Thus, by January 305, Carausius had gained eight new allies in the Senate.
In early January, the senators investigating Tetricus' death instructed their spies in Belgica to learn as much as they could about the unit that Allectus commanded. During the latter half of the month, the spies began learning what they could. A turning point came when one agent learned that the two soldiers who were rumored to have begun receiving substantial pay raises had been absent for roughly two weeks before and after the date of Tetricus' death. That agent quickly reported that information to the senator he was working for. The report reached Colonia Agrippina in early February. By that time, Carausius had replaced another eleven senators and bribed or intimidated six others into supporting him. The Postumians knew it was time to act.
The senators who had taken the leading role in the investigation began to share their findings with their colleagues, including the senior senator. The senior senator was responsible for presiding over the Senate whenever the emperor was absent from a Senate meeting, and he had the right to convene the Senate. The Postumians wished for him to convene the Senate for the purpose of holding a vote to depose Carausius. The senior senator agreed to this, and also agreed to a request by the Postumians to ensure that Carausius' allies in the Senate would not learn about the meeting until the last minute, so that Carausius would be unable to manipulate the outcome. The meeting was to be held on February 16 after dark. (For the Senate to assemble or continue a meeting after dark was not unheard of, but it was very rare.)
The Overnight Senate Meeting
At dawn on February 16, the Senate assembled for a seemingly normal meeting. Carausius attended that meeting. The meeting ended by late afternoon. Then at twilight, word began spreading that the senators were to come to the Senate chamber as soon as possible for a meeting.
It was dark by the time the meeting began. The senior senator announced that the purpose of the meeting was to hold a vote on whether to depose Carausius and replace him with Arpagius. He then described the evidence that Carausius was involved in the murder of Tetricus that had been collected up to that point. He also discussed the interpretation of the rules of proceedings that had been created to justify the meeting and the vote. Under the rules of proceedings, three days had to pass after a bill or resolution was introduced before it could be voted on, but the senior senator deemed the resolution to depose Carausius and replace him as First Citizen with Arpagius to have been introduced no later than the day he agreed to call the meeting. Also, the rules required that each senator be allowed to speak before the vote, but the senior senator clearly stated that the vote would be held by dawn, regardless of whether or not every senator had spoken: the senior senator stated that any senators who had not spoken by dawn would be deemed to have waived their right to speak by allowing their colleagues to speak for too long.
Most of the Postumians made only brief statements, although several gave speeches in which they either defended the notion of a strong Senate or warned that allowing Carausius to ascend to the emperorship by murdering the current emperor would set a dangerous precedent. Most of the Princepist senators gave long speeches in which they passionately defended the First Citizen and protested the nature of the meeting, mainly on procedural grounds; and some went so far as to argue that even if the accusations were true, Carausius' actions were justifiable. Some of the senators who were not in either faction gave speeches in which they argued either that Carausius was unqualified to begin with or that he did not deserve to rule because he had been involved in a murder. The last senator to speak was a Princepist. Like many of his colleagues, he condemned the meeting on procedural grounds; but he also harshly condemned the interpretation of the rules that was being used. After he finished speaking, he walked out of the chamber. Seventy-four other senators quickly followed, sixty-two of whom were Princepists, five of whom were from the "strong leadership" bloc, and seven of whom were not obviously aligned with any major faction.
After the mass walkout, there was still a quorum in the Senate chamber, so the vote was held. (For the purpose of voting to depose and replace the First Citizen, a quorum was defined as 60% of the Senate, or 150 out of 250 senators.) By a vote of 129 to 46, the Senate voted to depose Carausius and appoint Arpagius the new First Citizen. The Senate went further: it declared that in the event that Arpagius died before he learned of his appointment or before he could name his successor, Tetricus the Younger would succeed him.
Aftermath of the Overnight Senate Meeting
Shortly after the vote was held, the senior senator sent out letters to Arpagius and Tetricus the Younger informing them of the Senate's decision. The messengers tasked with delivering these letters left Colonia Agrippina while it was still dark. At that time, Arpagius was the governor of the province of Massiliensis and living in the province's capital, Massilia (OTL Marseille), so the news would not reach him for over a month.
During the morning of February 17, word of the overnight meeting quickly spread through Colonia Agrippina. Shortly before noon, Carausius publicly announced that he would not recognize the Senate's votes, repeating the multiple complaints on procedural grounds that his allies had made the night before. Later that day, he announced that he would expel and replace every senator who had voted to depose him. The senior senator responded by declaring that the Senate had no reason to recognize that decree, as they had already deposed Carausius. By the end of the day, both Carausius and the senior senator had stated that they were prepared to use force against the other.
The First Battle of Colonia Agrippina
For several days, the situation inside Colonia Agrippina was tense, but remained nonviolent. Both Carausius and the senators who voted to depose him each continued to assert that the actions of the other side were invalid. Civil officials and military commanders began choosing sides. While waiting to gain enough support to make a move against the other, each faction tried to operate as the government as much as possible. The senators who had voted to depose Carausius and make Arpagius the First Citizen in his place continued to meet in the Senate building, while the senators who had either walked out of the overnight meeting or stayed and voted against deposing Carausius met in the imperial palace and acted as a separate body.
The First Gallic Civil War began on February 24, 305. In the middle of the morning, Carausius ordered soldiers loyal to him to seize the Senate building and arrest the senators who had voted against him. The Senate building was heavily guarded, and there were several hundred pro-Arpagius soldiers in the neighborhood in which the building was located, so a clash between the pro-Carausius and pro-Arpagius forces ensued. The pro-Arpagius Senate was in session when the fighting began, and its members began evacuating the building shortly after the fighting started. The entire pro-Arpagius Senate was able to get out of the building and move to a house deeper inside the part of the city controlled by the pro-Arpagius Senate. By the end of the day, the pro-Arpagius forces had managed to hold all of the neighborhoods that they had been in control of before the battle began. The next day, Carausius ordered a larger force to attack a different pro-Arpagius neighborhood, but the pro-Arpagius forces were again able to hold the line.
On February 26, the situation changed. The pro-Carausius forces repeatedly attacked a single point in the pro-Arpagius group's defenses, and eventually breached the latter's defenses at that point. Within a couple of hours, Carausius controlled the entire capital city. Several of the pro-Arpagius senators had already left, but most were still in the city when the pro-Arpagius line was breached. Most were able to escape, but ten were captured and fourteen were killed.
Course of the war
After the First Battle of Colonia Agrippina, the pro-Arpagius Senate briefly stayed in Bonna (OTL Bonn), and then relocated to Augusta Treverorum (OTL Trier). Most of the military commanders stationed in and around Augusta Trevorum had been friends and close associates of Tetricus, so the pro-Arpagius senators believed they would be safe there. From Augusta Treverorum, they continued to command forces opposed to Carausius' rule.
Little happened during the month following the pro-Arpagius Senate's escape from Colonia Agrippina. Word of the deposition of Carausius and Carausius' refusal to recognize the deposition spread through the Gallic Empire. Military commanders and civil administrators chose sides as they learned what happened. In every province, there were at least a few towns where the local officials would choose the side opposite of the side chosen by the provincial governor. Most of the legions in the army were more unified: when the general in command of a legion aligned with either candidate, most of the lower-level commanders in that legion would accept the decision; and any commanders who were suspected of not honoring the general's choice would either be replaced or chased away from where the legion was stationed.
Arpagius himself learned that he had been appointed First Citizen on March 24. Over the following few days, he was able to learn about the subsequent events. This was because most of the civil and military officers who had sided with him sent him letters informing him of their decision and informing him about the most recent developments. This enabled Arpagius to quickly begin formulating a strategy to take Colonia Agrippina. On March 27, Tetricus the Younger learned that Arpagius had been appointed First Citizen and that he was the Senate’s second choice. He quickly announced his support for Arpagius.
By the time that Arpagius, who was in Masillia, learned that he had been appointed First Citizen, almost everyone in northeastern Gaul had chosen a side. On March 20, the first battle since the one in Colonia Agrippina began. This was the Battle of Bonna. Bonna was the only major city in Germania Inferior and the closest major city to Colonia Agrippina to side with Arpagius, so Carausius sent a whole legion to take the city. Carausius intended for his forces to march on Augusta Treverorum immediately after taking Bonna. On the first day of the battle, Carausius' forces managed to get deep inside the city. While the pro-Carausius forces were taking parts of the city, however, approximately 400 pro-Arpagius soldiers (the majority of whom were archers) removed their armor, donned civilian clothing, and waited in neighborhoods that seemed like they would imminently be taken by Carausius' men. When Carausius' forces came, these soldiers hid their weapons. Fighting continued through the night. Shortly before dawn, the pro-Arpagius archers who had posed as civilians gathered their weapons, made their way to buildings near the front lines, and began shooting pro-Carausius soldiers. Besides killing or wounding several dozen pro-Carausius soldiers, this distracted the pro-Carausius soldiers and forced the captain in that area to send men to find the shooters. This allowed the pro-Arpagius forces to break through the pro-Carausius line and retake much of Bonna before the pro-Carausius forces could react. By late morning, most of Bonna had been retaken. 1800 of Carausius' soldiers fled the city, while 2,100 were killed during the battle, and 800 were trapped inside the city and surrendered. As for Arpagius' forces, those stationed in and around the city only numbered 4,100 when the battle began, and 1600 of them were killed.
April – May 305
By April, only central and western Spain and Amasiga still had yet to learn that there was a civil war in the Gallic Empire. North of the Pyrenees, it had become clear which areas each side controlled. Most of northern and western Gaul and Britannia Superior had sided with Carausius. Arpagius, on the other hand, was recognized in central and southern Gaul, eastern Spain, and Britannia Inferior. Each side also had exclaves of support in areas that were otherwise aligned with the other side.
One feature of Arpagius’ provisional regime that emerged by April was that the military command was decentralized. Before Arpagius learned that he had been appointed First Citizen, the pro-Arpagius Senate commanded the army units that recognized Arpagius. This continued after Arpagius learned of his appointment because the pro-Arpagius Senate was far away from Arpagius himself. Similarly, Tetricus the Younger was a considerable distance from Arpagius, so the pro-Arpagius forces in the area where he was looked primarily to him for leadership. It was only in southern Gaul where Arpagius exercised direct authority. Both the pro-Arpagius Senate and Tetricus the Younger had told the officers that took orders from them that Arpagius’ orders were to supersede their own.
On April 2, Arpagius began sending out orders to multiple legions to meet in Divodurum (OTL Metz). His plan was for a large force to march on Colonia Agrippina and arrest Carausius, which he believed would lead to a quick end to the war. What he did not know was that after the Battle of Bonna, Carausius and his Senate had left Colonia Agrippina for Turnacum (OTL Tournai).
At the same time that Arpagius was preparing to take Colonia Agrippina, both Carausius and Tetricus the Younger were planning campaigns of their own. Tetricus the Younger wanted to take control of a strip of land extending through northern Gaul to the Oceanus Britannicus (OTL English Channel), thereby isolating the western half of Carausius' core territory from Carausius. Carausius, meanwhile, was planning an invasion of the eastern half of Belgica (which was under the control of Arpagius' Senate) that would culminate in the capture of Augusta Treverorum.
By the last week of April, both Carausius and Tetricus the Younger were ready to begin their attacks. The force loyal to Tetricus the Younger had gathered near Avaricum (near OTL Bourges). The legions loyal to Carausius were waiting on the north side of the border between Germania Inferior and Belgica near the Mosa River (OTL Meuse River). Carausius' forces attacked first, on April 24. The forces of Tetricus the Younger began moving through northern Gaul two days later. At that point, Arpagius had travelled as far as Lugdunum (OTL Lyon).
Carausius' forces attacked Arpagius' defenses at a relatively weak point, so they were able to break through on April 26. Over the subsequent few days, they moved southward, taking several small towns. On April 30, Carausius' forces split into two groups: one would continue moving southward, and the other turned eastward toward Divodurum and Augusta Treverorum. At the same time, Tetricus the Younger's forces won their first battle on April 29. This was the Battle of Noviodunum Biturigum (OTL Neung-sur-Beuvron).
During the beginning of May, the forces loyal to Carausius who were moving southward through Belgica took over several small towns. They were moving though an area that Arpagius and his supporters did not consider strategically important, so those towns fell with little resistance. Things were more difficult for the units heading for Divodurum. Divodurum was close to Augusta Treverorum, so the pro-Arpagius Senate had stationed several legions around it. The units heading for Divodurum clashed with pro-Arpagius units just east of the Mosa River twice during the first week of May. Both times, the forces loyal to Arpagius blocked the forces loyal to Carausius.
At the same time that the pro-Carausius forces were campaigning in Belgica, the forces commanded by Tetricus the Younger were continuing to advance northward. On May 11, they reached the outskirts of Aurelianum (OTL Orléans). A large number of forces loyal to Carausius had been sent to Aurelianum, but not all of them had arrived by the time Tetricus the Younger and his men arrived. The pro-Carausius forces initially fled the city, but returned in greater numbers on May 13. Tetricus the Younger's forces retreated from Aurelianum on May 14. At first, they attempted to move east, toward Senones (OTL Sens), but they were soon forced to go back to Noviodunum Biturigum.
Meanwhile, Arpagius was continuing to move northward. As he approached Belgica, he learned about the invasion of eastern Belgica. Arpagius' destination was still Divodurum, and the path of the pro-Carausius forces was in the general direction that Arpagius was traveling, so intercepting the pro-Carausius forces required a minor detour by Arpagius' forces. Arpagius began sending out scouts to find the pro-Carausius units on May 9. By that time, Arpagius and his forces were just south of the Arar River (OTL Saône River).
Arpagius crossed the Arar and entered Belgica on May 13. The next day, the units that were with him split up into six groups and fanned out, hoping to intercept the pro-Carausius units. On May 17, two of the groups that had been with Arpagius learned where the pro-Carausius forces were, and they quickly sent messengers to inform the other groups. Three of the pro-Arpagius groups converged and intercepted the pro-Carausius force on May 20. The pro-Carausius force was decimated. The survivors tried to escape, but were caught or killed by Arpagius' other units within two days. Arpagius' entire force then proceeded toward Divodurum, annihilating the pro-Carausius units that had been attempting to invade the city along the way. Arpagius and his men arrived at Divodurum on May 27.
News of the beginning of the war reached the eastern Spanish provinces by the end of March. The governors of the provinces of Ilercavonia and Vasconia (both of which were eastern Spain), as well as the duces of the military districts to which those provinces belonged, decided to pre-emptively invade the provinces of Asturia and Carpetania because the governors of both provinces were known allies of Carausius. The goal of the invasion was to replace the governors of both Asturia and Carpetania with pro-Arpagius governors. The campaign began on April 14 with an invasion of eastern Carpetania. Also, pro-Arpagius forces from Vasconia began travelling through the province of Cantabria to Asturia on April 20.
The pro-Arpagius forces rapidly took control of Carpetania. The news of the political crisis in Colonia Agrippina reached the eastern and northern areas first, and the majority of the officials in those areas had been allies of Tetricus the Elder. The invasion of Carpetania was a success because the leaders in eastern Spain learned about the war before the word reached the rest of the peninsula and quickly agreed to attack, but also because there were a many low-ranking army commanders in the province who had been loyal to Tetricus the Elder. The governor of Carpetania surrendered and was removed from office on May 4.
The invasion of Asturia was not as easy as the invasion of Carpetania. By May, word of the Senate's vote to depose Carausius, Carausius' refusal to recognize the Senate's decision, and the First Battle of Colonia Agrippina had finally reached Asturia; and word of the first few battles fought in Carpetania arrived during the first week of May. The governor of Asturia quickly began ordering the military forces under his command to prepare for an invasion. He also reached out to centurions and military tribunes in the forces under the command of the dux who he knew to be pro-Carausius, asking them to find ways to seize control of the legions they were serving in. The Vasconian forces reached the border of Asturia on May 4. The provincial military forces were very much unprepared, but they knew to expect an invasion. They were able to fight off the initial attacks. The situation changed by the middle of May, however. As soon as the governor of Carpetania surrendered, the majority of the pro-Arpagius forces moved on to Asturia, and were joined by forces from Vettonia and northern Lusitania. These units arrived at the border of Asturia on May 22. The pro-Carausius forces were not able to withstand the attacks, and Asturia fell to the supporters of Arpagius by June 6.
After the fall of Carpetania and Asturia, supporters of Arpagius controlled all the important political and military offices in Spain. They quickly purged supporters of Carausius from the lower political offices and army commands. Some supporters of Carusius were imprisoned or executed, but most were allowed to resign from office. Sporadic resistance would continue throughout Spain through the end of July.
After Amasiga was made part of the Gallic Empire, Tetricus the Elder had been careful to prevent anyone with connections to Carausius from being appointed to any civil or military office there. When the news of the events in Colonia Agrippina reached Amasiga, the province immediately joined Arpagius' side.
The Second Battle of Colonia Agrippina
Even before Arpagius arrived at Divodurum, he began planning his attack on Colonia Agrippina. By the time he arrived, neither he nor his Senate knew that Carausius was no longer there.
Arpagius had brought three legions and six auxiliary units to Divodurum. There were two legions and five auxiliary units already stationed in northeastern Belgica, and one legion protecting Bonna. Arpagius wanted all the units he had led and two auxiliary units that were already in Belgica to march to Colonia Agrippina. He wanted the legion stationed at Bonna to arrive at the city at the same time as his forces. In order to ensure that the legion from Bonna would arrive at Colonia Agrippina at the right time, Arpagius sent the instructions to the general at Bonna two days before he and his forces left Divodurum.
The pro-Arpagius units converged south of Colonia Agrippina shortly after dawn on June 7. Even though Carausius had abandoned Colonia Agrippina, he had left two legions in and around the city. Arpagius, however, had four legions and eight auxiliary units with him, meaning that Arpagius' forces outnumbered the pro-Carausius force by well over two to one. The generals commanding the pro-Carausius legions realized they were outnumbered before the battle started, so they decided it would be best to simply evacuate the city. Arpagius and his forces arrived at the outskirts of Colonia Agrippina in the middle of the day. By that time, only a few hundred of the pro-Carausius soldiers had left. Arpagius quickly realized that his forces had the advantage and that the pro-Carausius forces were retreating. Rather than let the pro-Carausius forces go, Arpagius ordered two of his legions and two of his auxiliary units to march to the area just west of the city to intercept any pro-Carausius soldiers attempting to get away and attack the city from the west. The capital fell to Arpagius and his forces by the end of the day. Approximately nine hundred pro-Carausius soldiers managed to escape, but the rest were killed or captured. Arpagius' forces lost over seven hundred men.
After the battle, Arpagius' men searched for Carausius and the senators who had sided with him, but it quickly became clear that they had left the city long before the battle started. Arpagius had the pro-Carausius commanders brutally interrogated in order to learn where Carausius was. None of the commanders who had been stationed in Colonia Agrippina knew where Carausius was, however: when Carausius left Colonia Agrippina, he did not say where he was going; and after he arrived at Turnacum, he had instructed the local military commanders and civil officials to keep it a secret that he was there.
On June 9, three of the legions and four of the auxiliary units that had taken Colonia Agrippina left the city. Two legions and two auxiliary units moved westward, while one legion and two auxiliary units moved north. Arpagius stayed in Colonia Agrippina.
The pro-Arpagius forces that headed northward arrived at Novaesium (OTL Neuss) on June 10. They were able to take the city, but not without resistance. Many of the pro-Carausius soldiers who had escaped from Colonia Agrippina had arrived there on June 8 and told the local commanders what had happened, and the local commanders in turn had called for re-inforcements from cities and forts further north. The Battle of Novaesium began before the re-inforcements arrived. By the late afternoon of June 10, the pro-Arpagius forces had pushed their way into the center of the city; but by that time, pro-Carausius forces from Tricensimae (OTL Xanten) had arrived at the edge of the city. It was not until June 12 that Novaesium was fully secured. After the Battle of Novaesium, Arpagius instructed his forces not to try to move further north. Instead, he deployed spies into Carausius' territory to figure out where Carausius was.
After Tetricus the Younger's failed attacks on Aurelianum and Senones, he had ordered one legion and two auxiliary units to join him in Noviodunum Biturigum. These units arrived in early June, and Tetricus the Younger decided it was time to invade Carausius' territory on June 10. Since he had received word that more forces loyal to Carausius had been sent to both Aurelianum and Senones over the prior few weeks, he chose to bypass both cities and head straight for Lutetia Parisiorum (OTL Paris).
Between Aurelianum and Senones, there was a narrow corridor where Carausius' forces had little presence. Tetricus the Younger's forces passed through that area. Tetricus the Younger went straight to Lutetia Parisiorum, even bypassing several small towns along the way. Tetricus the Younger's forces arrived at Lutetia Parisiorum on June 18. Carausius was not unprepared. He had anticipated Tetricus the Younger would attack that city, so he had stationed one legion and four auxiliary units there. Tetricus the Younger arrived at Lutetia Parisiorum on June 21. His forces took the city after three days of fighting, but they sufferred heavy casualties, and were not able to advance farther into Carausius' territory. Carausius' forces did not immediately attempt to retake Lutetia Parisiorum, but over the following week they did secure the passageway to the city that Tetricus the Younger had used.
Prior to June, none of the generals or provincial governors in Britain actively got involved in the civil war. (At the same time, neither of the claimants to the purple were paying much attention to Britain.) This changed in early June, when the governor of Britannia Inferior, Flavius Dannicus, and the dux of Britain, Julius Proculus, agreed to take the initiative of invading Britannia Superior.
The British theater of the war began on June 12. Two events happened that day. One was that Dannicus led an attack on the city of Glevum (OTL Gloucester), which was right on the border between the two provinces. The other event was that Proculus led three legions across the River Nene, a river which served as the eastern segment of the border between the provinces. Glevum was well-protected, so Dannicus was forced to retreat on June 13. On the other hand, Proculus was more successful. Proculus' forces split up into several groups that each crossed the Nene at a different point. Rather than crossing existing bridges, which were heavily guarded, Proculus' men either built wooden bridges (which they burned after crossing) or swam across the river at points that were not close to existing bridges. All of the detachments were able to wipe out or chase away the small number of pro-Carausius forces they encountered. After Proculus' army regrouped, it first attacked the forces stationed near the bridges over the Nene; and then after securing the bridges, it turned southeast. Even though Proculus' goal was to capture Londinium (OTL London), he believed that the governor of Britannia Superior, a man named Lucius Durus, would be most prepared for an attack from the north; so Proculus' plan was to go around Londinium and then attack it from the east, southeast, and south.
On June 20, Proculus was intercepted by pro-Carausius forces about halfway between the Nene and the river Tamesis (OTL Thames). The pro-Carausius forces consisted of five auxiliary units. Even though the pro-Carausius forces were outnumbered, they managed to outflank Proculus' force. Proculus' men sustained many casualties and were forced to flee eastward. Taking Londinium would not be an option for a while. Instead, Proculus' new plan was to take control of Camulodunum (OTL Colchester).
Also on June 20, Dannicus made a second attempt to penetrate the border of Britannia Superior. He led his forces across the River Sabrina (OTL Severn) a considerable distance east of Glevum. This time, Dannicus and his men passed through a rural area, so they were able to advance rather easily. They took several small towns with almost no resistance during the remainder of the month.
June ended with little activity in Gaul, and July began the same way. After the Battle of Novaesium and the First Battle of Lutetia Parisiorum, Arpagius and Tetricus the Younger began drawing forces from the interior of Gaul. Likewise, Carausius sent re-inforcements from the interior of the territories under his control to the front lines.
Fighting in Gaul resumed on July 5. On that day, two legions loyal to Tetricus the Younger began a campaign to reopen the corridor between Lutetia Parisiorum and the rest of the territory under Arpagius' control. Two days later, a legion to Carausius arrived at the outskirts of Lutetia Parisorum to retake the city from Tetricus the Younger. At first, the pro-Carausius forces were able to make significant gains in the city. However, the two pro-Arpagius legions were able to overwhelm the pro-Carausius forces that had been blocking the path to Lutetia Parisiorum. Tetricus the Younger's re-inforcements reached the city by July 14. By July 15, Carausius' forces had been completely pushed out of the city. Tetricus the Younger seized several villages near Lutetia Parisiorum, during the following three days, but chose not to advance farther north for a while. On July 21, however, he ordered another attack on Aurelianum. This time, his forces were able to take the city.
Meanwhile, Arpagius decided it was time to advance westward. His territory only extended a few km west of Colonia Agrippina and Novaesium, and he knew that Carausius was sending more troops to the front line. He decided to attack before those troops could arrive. On July 6, Arpagius had two legions and eight auxiliary units attack Carausius' line at three different points near Colonia Agrippina. His forces broke through at the northernmost point in Carausius' defenses during the evening of July 7, and the central point by the afternoon of the following day. On July 8, the two auxiliary units attacking the third point of Carausius' line were redeployed to the areas where Carausius' line had been breached, leaving behind a legion to hold the line as it was. Over the following week, Arpagius' forces battled units encamped near the front lines, as well as newly arriving forces. At the same time, two legions arrived from the interior of Arpagius' territory. One of these legions stayed to defend Colonia Agrippina, and the other joined the battle. During the latter half of the month, Arpagius slowly gained territory. By the end of the month, his forces had advanced as far as the town of Durum (OTL Düren).
In Britannia Superior, July commenced with the fall of Corinium Dobunnorum (OTL Cirencester) to Dannicus. Dannicus and his forces reached Corinium Dobunnorum on July 2. Only minimal defenses had been stationed in the city, as Lucius Durus had not been expecting the city to be attacked, so the city was fully under Dannicus' control by July 4. Dannicus' goal was to create a corridor from the Sabina River to the Oceanus Britannicus, through which men could march and then sail to the continental provinces. On July 7, Dannicus resumed his southward charge. By July 16, Dannicus and his men reached Venta Belgarum. By this time, however, Durus had had a chance to react to the invasion, and had prepared for an attack on that city — as well as several nearby coastal cities. Dannicus and his forces were able to take Venta Belgarum by July 19, but Dannicus chose to pause his advance after that. On July 22, he summoned three additional auxiliary units to Britannia Superior, and these units arrived on July 31.
On July 2, Proculus and his forces reached Camulodonum. The city fell with little resistance. Durus had sent troops to the city, but they were not able to arrive in time. During the next couple of days, Proculus took several coastal villages near the city. On July 7, he sent two ships to Britannia Inferior to request re-inforcements. The ships arrived at a harbor in Britannia Inferior on July 11. Units began departing Britannia Inferior for Camulodonum on July 16. By the end of the month, six auxiliary units had arrived in Camulodonum.
August began with Arpagius continuing his westward push. His goal was to gain control of everything up to the Mosa River (OTL Meuse). During the first week, he continued to advance, but then his progress began to stall. His forces were becoming stretched: each time he moved from one town to the next, he would leave at least a small contingent of soldiers behind to guard the newly-taken town, leaving him with fewer men on the front lines.
After having secured both Aurelianum and Lutetia Parisiorum, Tetricus the Younger had paused his advance. During this time, he developed a new strategy: rather than continue taking large cities, he would take over a swath of small towns and rural areas, where Carausius' military had a weaker presence. Tetricus the Younger began executing this new strategy on August 8. He ordered two legions to march northeast toward the Oceanus Britannicus (he himself chose to stay in Lutetia Parisiorum). They were to fan out and take control of every town or village in their path. They were to avoid the cities of Rotomagus (OTL Rouen) and Samarobriva (OTL Amiens).
Tetricus the Younger's strategy quickly seemed to prove successful. Within ten days, the two legions he had sent out had covered half the distance to the Oceanus Britannicus. However, word of the offensive quickly reached the commanders in nearby cities, and they promptly began planning a counterattack. On August 20, a legion from Samarobriva intercepted Tetricus the Younger's forces, and managed to not only halt their advance but also recover several towns for Carausius. The pro-Arpagius legions were able to stop the pro-Carausius legion's counteroffensive, but they were not able to resume their offensive.
On August 1, Proculus led a legion and four auxiliary units westward from Camulodonum in another attempt to take Londinium. His forces covered half the distance to Londinium within a week. At the same time, the additional forces that Dannicus had called for allowed him to continue his campaign toward the Oceanus Brittanicus. He headed southeast, toward Noviomagus Reginorum (OTL Chichester). As Dannicus advanced, Durus diverted troops from the areas surrounding Londinium to combat Dannicus. Durus also sent a letter to Carausius, urging Carausius to send at least two legions to Britain.
Proculus approached the outskirts of Londinium on August 12. By this time, an additional legion had joined him, and another was on the way. One of the legions and two of the auxiliary units moved to a position northwest of the city, while the other units moved to a position south of the city. Both groups began their attack on the morning of August 13. Late in the afternoon, the third legion arrived. Durus' forces were outnumbered and outflanked. The following morning, he ordered his commanders in the city to surrender to Proculus.
Aftermath of the Battle of Londinium
After the Battle of Londinium, Proculus had Durus arrested. He installed one of his generals, named Julius Trenus, as the new governor of Britannia Superior. Some of the commanders who had been loyal to Durus accepted the new governor and laid down their arms. Others, however, refused to accept defeat. Some pro-Carausius generals chose to continue the fight in Britannia Superior, while others evacuated their forces to the continental provinces.
The only significant battle that took place after the fall of Londinium was the Battle of Noviomagus Reginorum, which began on August 17. The pro-Carausius forces that were already guarding that city were joined by forces from areas near Londinium who had refused to recognize the new governor. Dannicus was initially driven away from the city, but reinforcements sent by Proculus arrived on August 19. Dannicus was able to penetrate the city by August 20. By August 22, all of the pro-Carausius units had either surrendered, been killed, or escaped to Gaul.
A total of two legions and five auxiliary units loyal to Carausius arrived in Gaul from Britain during late August. Carausius was disturbed to learn that he had lost Britannia Superior, but he believed that the newly arriving forces could serve him well in his continental territories. Some were sent to fight Arpagius and Tetricus the Younger, while others were simply ordered to defend the coast against any attack from Britain.
The loss of Britannia Superior shook the confidence of some of Caurausius' generals, governors and senators. Carausius had been at a disadvantage from the beginning, and he had only steadily lost ground since April. Desertions had already become a problem for Carausius' army. As word of the takeover of Britannia Superior by Proculus spread, some of Carausius' officials began to question their loyalty to him.
News of the events in Britain reached the areas under Arpagius' control in early September, and it significantly boosted the morale of the pro-Arpagius soldiers on the front lines. The pro-Carausius generals tried to keep the news of the loss of Britannia Superior as contained as possible, so as not to weaken the morale of the foot soldiers; but with units from Britain arriving at the front lines in Gaul, the events in Britain gradually became common knowledge.
On September 3, Tetricus the Younger attempted another offensive in northern Gaul. He had had spies probe the pro-Carausius lines for weaknesses for several days, and his spies believed they had identified two weak points. Tetricus the Younger ordered his forces to attack both of those points. It turned out that one of those points was better-defended than the spies had believed. Tetricus the Younger was able to break through the pro-Carausius lines and retake several villages, but was not able to advance very far. Then on September 14, Tetricus the Younger summoned several units under his command that were stationed in Aurelianum to march to where the pro-Carausius forces were encamped and attack them from a position opposite that of Tetricus the Younger. These units arrived at the pro-Carausius encampment on September 21. The next day, both groups attacked the pro-Carausius legion. The pro-Carausius legion was outnumbered and outflanked, so it was forced to retreat to Samarobriva. On September 25, Tetricus the Younger began moving northwest again. On September 28, however, his progress was once again stalled by the same legion, which had left Samarobriva and fanned out in order to intercept his forces. Tetricus the Younger would spend the following two weeks fighting off attacks from the legion from Samarobriva.
In early September, Carausius ordered a legion that had fled from Britain to open up a new front in Gaul. To this end, the Britannian legion seized several villages north of Augustodunum (OTL Autun) between September 9 and September 12. Arpagius had stationed a legion at Augustodunum to protect it. The pro-Arpagius legion was able to repel the pro-Carausius legion, but they were not able to retake all of the villages that the pro-Carausius legion had taken. Then on September 19, a detachment from the pro-Carausius legion began marching eastward, away from the main part of the legion. By the next day, after marching almost 30 km, they turned southward and began attacking villages under Arpagius' control. Other units loyal to Arpagius stationed nearby counterattacked this detachment. Meanwhile, the legion at Augustodunum engaged in several skirmishes with the main part of the legion from Britain.
Sporadic fighting in Britannia Superior continued until the end of August. During September, Proculus focused on consolidating his control over Britannia Superior. The local military forces were relatively easy to bring under his control: the majority of the foot soldiers and lower-level commanders were apolitical: they had fought for Carausius only because Durus and the generals whose command they were under supported Carausius. Proculus and Trenus replaced the majority of the generals and senior officers who had been loyal to Durus. (Most of them were simply dismissed from the army: only a few were arrested.) Some units that had fought for Carausius were merged with units that had fought for Arpagius; but most of the former pro-Carausius units were left intact, albeit with new commanders.
On September 16, Proculus, Dannicus, and Trenus met in Londinium. They spent the next three days formulating plans for an invasion of northern Gaul. Thereafter, Dannicus left Britannia Superior and began traveling back to Eboracum (OTL York) the capital of Britannia Inferior. He ordered one third of the forces under his command to leave with him. The other two thirds were to stay behind to guard Britain against an invasion by Carausius' forces and participate in the planned invasion of northern Gaul.
Messalla, the Roman emperor, had first learned of the Gallic civil war in May. At first, he opted not to get involved in any way. He believed that a direct conflict with the Gallic Empire would be too dangerous. By September, however, it seemed to him that the civil war could last for a long time (based on news he had heard of the situation as of July), so he felt he could use the situation to the Roman Empire's advantage.
Messalla sent three legions to Pannonia and Noricum, the two regions which, during the Gallic War for Independence, had been conquered from the Roman Empire by Germanic tribes that had allied with the Gallic Empire. Messalla intended to reconquer Pannonia and Noricum while the Gallic Empire was divided against itself. He also deployed three legions to northwestern Italy to defend Italy against any counterinvasion by the Gallic Empire.
The Roman legions began their invasion of Pannonia and Noricum on September 22. The two countries they invaded were Marcomannia and Suevia. The governments of both countries were caught off guard, so the Romans were able to take everything south of the Savus River (OTL Sava River) by the end of the month.
On October 4, four legions and ten auxiliary units set sail from Britain to northern Gaul. Two of the legions and five of the auxiliary units sailed to Augustodurum (OTL Bayeux), while the rest of the units sailed to an area north of Rotomagus. The two groups landed on October 6 and October 7, respectively. The invasion of Augustodurum was a success. Only one legion was stationed at Augustodurum, so the invasion force easily overwhelmed that legion. During the three days after the Britannian forces took the city itself, they seized control of every town within several km of the city. The other half of the invasion force was equally successful. There were no major cities near the area where those units had landed, so they were able to advance from the coast all the way to the outskirts of Rotomagus within two days of landing. Like Augustodurum, there was only one legion defending Rotomagus, so Rotomagus fell to forces loyal to Arpagius on October 11.
After the Battle of Rotomagus, the Britannian generals made contact with the commanders serving under Tetricus the Younger. Tetricus the Younger ordered one of the legions to help him defeat the legion from Samarobriva. On October 15, the legion (accompanied by two auxiliary units) marched northeast from Rotomagus, then split into three groups and moved southward. Two of the groups, which together made up half the legion and one of the auxiliary units, would attack the Samarobriva legion from two different positions to its north, while Tetricus the Younger would attack from the south. Meanwhile, the other half of the legion and the other auxiliary unit would attack Samarobriva itself. The co-ordinated attacks on Samarobriva and the legion stationed there all occurred on October 20. The city fell, and the majority of the legion was wiped out.
After the Battle of Samarobriva, Tetricus the Younger was in control of a corridor through Carausius' territory. He next sent two legions to take Senones. Senones fell to Tetricus the Younger on October 26. Meanwhile, one of the legions in Augustodurum was carrying out a southward offensive. That legion took the city of Suindinum (OTL Le Mans) on October 23.
By the end of the month, word had reached Turnacum that Carausius had been fully cut off from the eastern half of his territory. At this point, several of Carausius' generals and senators began meeting secretly and plotting to depose Carausius.
Pannonia and Noricum
During October, the Roman invasion of Pannonia and Noricum continued to progress rapidly, although all four of the states were fighting back. During the first week of October, the Marcomannian army was able to fight off the Romans several times. Alamannia and Quadium also entered the war, and the presence of their forces on the front lines helped slow the Roman legions.
Suevia's response to the invasion had been poorly organized, and as a result it was completely overrun by the Roman army by October 18. Quadian troops entered Suevia to assist the Suevians on October 10, but they came too late, and they withdrew after only four days. Even though Marcomannia resisted the Roman Empire more effectively, it had lost a third of its territory by the end of the month. Also, the Romans had seized several towns along the southern border of Alamannia.
Between October 8 and October 17, most of the Suevian leaders sent letters to Arpagius, begging him to send troops to Suevia's aid. The king of Marcomannia sent a request for aid to the Gallic Empire on October 9. The governments of Alamannia and Quadium sent out letters asking the Gallic Empire to help them on October 14 and October 19, respectively.
The End of the War
On November 8, a group of three generals and fourteen senators who had supported Carausius sent two hundred soldiers to the house where Carausius had been staying. These soldiers overwhelmed Carausius' bodyguards and arrested him. The senators and generals involved in the coup immediately sent out letters to all the generals who had supported Carausius, instructing them to immediately surrender and recognize Arpagius as the sole First Citizen of the Gallic Empire and Tetricus the Younger as his successor.
Within a couple of weeks, most of the pro-Carausius generals in the eastern half of Carausius' realm had received the orders to surrender. The majority of them obeyed, but a few disobeyed. This led to several battles between the forces loyal to Arpagius and Tetricus the Younger and the last army units commanded by supporters of Carausius during late November. Also, word of the downfall of Carausius did not reach his supporters in northwestern Gaul until mid-December. All of the generals in northwest Gaul announced their recognition of Arpagius between December 19, 305 and January 5, 306.
The Fate of Carausius and His Supporters
Arpagius ordered Carausius to be brought to Colonia Agrippina on November 27, 305. Carausius arrived on December 27. On January 20, 306, Carausius was put on trial for orchestrating the murder of Tetricus the Elder and leading a rebellion against Arpagius. The trial ended on January 24. Carausius was found guilty and sentenced to death, and this sentence was carried out on January 30.
Arpagius pardoned the senators and generals who had led the coup against Carausius, and he allowed them to keep their respective Senate seats and military commands. The remaining pro-Carausius senators were expelled from the Senate and put on trial for aiding the rebellion, and all but nine of them were convicted; and those convicted received sentences ranging from ten years in prison to death. Arpagius' treatment of generals and other high-ranking military officers who had supported Carausius was mixed. Some of the ones who had not actually engaged in combat against forces loyal to Arpagius were allowed to retain their ranks; but most within this category were demoted, and a few were dismissed from the army. All officers above the rank of centurion — as well as some centurions — who had actively participated in combat with supporters of Arpagius were expelled from the army and put on trial for rebellion against Arpagius; and most of these were convicted and sentenced to either life in prison or death. All the provincial governors and duces who had sided with Carausius were put on trial, found guilty, and sentenced to either life in prison or death. All of these proceedings were carried out between January and May of 306.
Arpagius' victory in the civil war was a victory for the Postumian faction of the Senate. The senators who were expelled for siding with Carausius were replaced with Postumians and people who simply desired a strong leader. By May 306, there were only five Princepists in the Senate — they were among the fourteen senators who had supported Carausius but then turned against him.
Carausius had justified rejecting the Senate's vote to depose him by holding that the Senate had severely violated its rules of proceedings. Arpagius accepted his election as First Citizen; but on March 4, 306, he admitted in a speech before the Senate that he had always been troubled by the interpretation of the rules of proceedings used to justify his election, and he urged the Senate to amend its rules of proceedings to prevent questionable interpretations from being used again.
The actual structure of the Gallic government did not change as a result of the war. Although Arpagius did not believe in stacking the Senate with his partisans or removing senators for opposing him, he did have the power to do so.
Pannonia and Noricum
Arpagius first learned about the Roman invasion of Pannonia and Noricum in late November 305. He immediately mobilized the Gallic army to help the Pannonian and Norican countries and attack the Roman Empire itself.