First Gallic Civil War (Gaul Rising)

Background
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, 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 cooperation 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 reinstate Postumus' policy of cooperation 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.)

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. In accordance with the Senate's rules of proceedings, each of the senators were given an opportunity to speak; although the senior senator clearly stated that the vote would be held by dawn, whether every senator had spoken or not. 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.