On paper, the Tetrarchy had been an excellent idea: two senior emperors (augusti) and two junior emperors (caesares) would rule over the vast Roman Empire in perfect harmony. When Diocletianus, who had designed the system, and his co-emperor Maximianus abdicated in 305, the system of succession seemed to be working well too. The caesar Constantius became the new augustus in the west and his colleague Galerius the new augustus in the east. Severus (in the west) and Maximinus Daza (in the east), both with close ties to Galerius, took their places as caesares. But the fact that they were so closely associated with Galerius, and that two other talented young men had been passed over, would lead to major problems. The keywords of the Tetrarchy were harmony and trust, values that would prove to be wholly absent in practice.
Two pretenders: Constantine and Maxentius
After joining his father Constantius back in 305, Constantine had accompanied the augustus on a campaign against the Picts in the north of Britannia. The next year, on 25 July 306, Constantius had died in Eburacum (York), the city where the emperor Septimius Severus had breathed his last breath almost a hundred years previously. According to the rules of the Tetrarchy, Severus would now become the new augustus and nominate a new caesar, with Constantine being an option. However, the troops in Britannia decided to proclaim Constantine the new augustus, as the direct successor to his father, and probably in complete conformity with Constantius’ own wishes. The army’s actions, which were no doubt not as spontaneous as they looked, were basically illegal. Galerius, who after the death of Constantius was the most senior surviving emperor, was now faced with a serious dilemma. Constantine was clearly calling the shots in Britannia, Gaul and Spain, the territories of his father. As taking military action against the son was risky, Galerius tabled a compromise in September: Constantine would be recognised as caesar under Severus, the new augustus.
Constantine, who was in his early thirties, had enough political experience to realise that, for the moment, he had to accept the compromise. He spent the rest of the year consolidating his power in the territories formerly controlled by his father. Moreover, a campaign against the Alemanni and Franks proved to be necessary, as these Germanic tribes had crossed the Rhine and had attacked Roman territory. Constantine tracked them down, defeated them in battle and took two Frankish kings prisoner, Ascaric and Merogais. The two men ended their lives in a particularly unpleasant way: they were thrown to the wild animals in the arena, possibly in Augusta Treverorum (Trier), where Constantine now set up his headquarters. It is possible that he immediately started the construction of his palace, the famous Aula Palatina, which is still extant.
In the meantime, Italy was in turmoil as well. On 28 October 306 Maxentius, son of the Maximianus who had abdicated, had staged a coup in Rome, supported by the people and the Praetorian guard. Maxentius was obviously still angry that he had not become caesar. The people, for their part, were angry with Galerius, who had decided that, for the first time in history, Rome and the area south of it – Italia Suburbicaria – had to pay the imperial taxes. Lastly, the same emperor had stated his intention to disband the praetorians and the equites singulares augusti, the mounted bodyguard of the emperor. These troops had once protected the life and limbs of the emperor, but in this role they had been supplanted several decades previously by the protectores, who were in their turn locked in a rivalry with new elite units, the scholae palatinae. The praetorians had nevertheless continued to receive their pay, and the prospect of losing their easy life due to Galerius’ plans made them rebellious. In fact, they became so rebellious that, according to Zosimus, they murdered the praefectus urbi Abellius when he tried to thwart their coup.
Upon assuming power, Maxentius had not taken the title of augustus or caesar. He simply called himself princeps, ‘first man’. However, Galerius – who was Maxentius father-in-law – was furious about the coup of his son-in-law and ordered Severus to expel the usurper from Rome. In the meantime Maxentius had been reunited with his father, who had left his estate in Lucania and had travelled to the Eternal City. In 305 the old emperor had abdicated most unwillingly and for the sole reason that Diocletianus had pressured him into doing so. The princeps Maxentius now reinstated Maximianus by appointing him augustus again. This meant that there were now three augusti: Galerius, Severus and Maximianus. In the winter of 307 Severus left his capital of Mediolanum (Milan) and advanced on Rome with a large army. The emperor managed to reach the third-century Aurelian walls of the city, but there his soldiers deserted him. Many of the men had previously served under Maximianus and were loath to fight against him. Probably even more important was the fact that Maxentius offered the soldiers large sums of money.
Severus was forced to retreat and entrenched himself in the highly defensible city of Ravenna. Maximianus persuaded him to surrender, after promising that his life would be spared. Severus was stripped of his purple robes and taken to Tres Tabernae, a stopover on the Via Appia southeast of Rome. There he was imprisoned as a hostage. Meanwhile Maximianus and Maxentius annexed Severus’ territories in Northern Italy and along the Danube. For the moment Galerius was powerless to intervene, as he was taken up by his own campaigns in the Danube region. Fully aware that the augustus would one day want to avenge the defeat of his friend Severus, Maximianus and Maxentius began searching for allies. One obvious ally was Constantine. Later in 307 Constantine and Maximianus held a meeting in Augusta Treverorum or Arelate (Arles). The men made an alliance, which saw Maximianus appointing Constantine augustus and Constantine marrying Fausta, the daughter of Maximianus and the sister of Maxentius. At the time Constantine had already been a widower for a couple of years: his first wife Minervina, the mother of his young son Crispus, had died at an unknown date.
The power struggle
Galerius was absolutely livid when he heard about the alliance between Constantine on the one hand and Maximianus and Maxentius on the other. He decided to no longer recognise Constantine as caesar and invaded Italy in September of 307 to deal with Maxentius once and for all. However, his campaign proved to be just as disastrous as that of Severus a few months previously. The emperor had far too few troops for besieging Rome, and again Maxentius spent lavishly on bribing the enemy soldiers. Ultimately Galerius had no other choice but to return to the Balkans, sacking a large part of Northern Italy on the way back. Severus had now outlived his usefulness for Maxentius. He therefore had him executed or forced him to commit suicide. The body of the former emperor was nevertheless treated with respect, and Severus found his final resting place in the mausoleum of the emperor Gallienus on the Via Appia. Maxentius then abandoned all modesty and began styling himself augustus as well. Moreover, he brought the Praetorian guard back to its traditional strength of 9,000-10,000 men. All these actions would lead to a heated conflict with his father.
After negotiating with Constantine, old Maximianus had returned to Rome. There he made plans to depose his son and take control of the city himself. On 20 April 308 he held a speech in the Forum Romanum in which he accused Maxentius of being the prime cause of all the misery that had befallen the Empire. Maximianus ripped off his son’s purple robes, but Maxentius was immediately rescued by the praetorians and the people. The old emperor was now forced to turn tail and run, fleeing Rome and seeking refuge at the court of his son-in-law Constantine in Gaul.
There was no denying that the situation in the Empire was now desperate. In order to solve the crisis, the defeated emperor Galerius had persuaded old Diocletianus to leave his palace in Salonae (Split) and become consul again. In addition, a conference was held in Carnuntum in the autumn of 308. Here Galerius, Diocletianus and – quite surprisingly – Maximianus met to talk about ending all internal strife. Diocletianus’ moral authority was still immense, and this proved to be the key to reaching solutions. Maximianus was again forced to abdicate, while his son Maxentius was not recognised as a legitimate emperor. Constantine, on the other hand, was recognised, albeit as a mere caesar. A certain Valerius Licinius Licinianus was appointed as the new augustus in the west, the successor of the slain Severus. Licinius was a Dacian who, as an officer under Galerius, had fought in the wars against the Persians. At Carnuntum, the Tetrarchy appeared to have been restored: Galerius and Licinius were the augusti, Constantine and Maximinus the caesares. Diocletianus had done his job well and could focus on growing cabbage again, a hobby he took great delight in.
Of course we all know things soon took a different turn. Maxentius – who was now basically a pariah – was faced with a rebellion in North Africa by the vicarius (governor of a number of provinces) Lucius Domitius Alexander. This brought the import of grain to Rome to a standstill, causing protests and riots in the city. Maxentius was forced to respond with violence, which seriously hurt his popularity. He was also unable to send out an expedition to defeat Alexander, as Italy was now being threatened by the new augustus Licinius. In 309 the latter made a half-hearted attempt to invade the peninsula, but it is generally assumed that he only got as far as Aquileia and was then forced to withdraw.
In the east of the Roman Empire, in the diocese of Oriens (which comprised Egypt, Palestine and Syria), the caesar Maximinus Daza had continued the persecutions of Christians that had been started by Diocletianus. In the west these had never gained momentum, and under the augustus Constantius they had been stopped altogether. Maxentius did not persecute Christians either. The Christian community in Rome was large enough to be a power factor, and Maxentius valued good relations with the Christians. It is not inconceivable that it was Maxentius who ceded a terrain along the Via Appia to the Christian community and gave them permission to build the Basilica Apostolorum there, a church that is currently known as San Sebastiano fuori le Mura. Daza, on the other hand, was a zealous persecutor of Christians. He has been described as “the only emperor who saw the conflict as a genuinely religious conflict”.
As early as 306 Daza had issued an edict that followed up on the obligation to sacrifice to the gods, which was part of Diocletianus’ fourth edict. That edict had been addressed to all Roman citizens throughout the Empire, but in practice it only applied to men. Daza’s edict went one step further, as it also specifically applied to women and children. Thanks to a census held by Galerius a list of taxable citizens was now available, which meant that the authorities now had a better idea of who to target during the persecution. Some Christians who refused to sacrifice were executed, among them Eusebius of Caesarea’s teacher, a certain Pamphilus. Moreover, several hundred Christians were deported to the mines, especially to the copper mines of Phaino in present-day Jordan. However, there cannot have been mass arrests, mass executions and mass deportations, for several reasons. The authorities simply lacked the troops to effectively enforce the edict, some authorities just ignored it or lied that it was applied, and some Christians made a sacrifice under duress in the hope of being forgiven later.
Daza temporarily halted the persecutions in July of 308 and then resumed them again in November of 309. We can only speculate why he did so. What is certain is that he was highly indignant about the outcome of the summit that had been held in Carnuntum. After all, not Daza, but Licinius had been appointed augustus. For this the caesar especially blamed his uncle Galerius. Galerius for his part tried to calm the tensions by granting his nephew the title of filius augusti – son of the augustus –, but it is impossible to prove whether it was this reward that led Daza to resume his persecutions at the end of 309. In any case, the caesar issued a new edict at the end of the year, which was likely as (in)effective as the previous one. There must have been a couple of new martyrs, but Christianity in the east was simply too big to eradicate. The caesar probably also had other duties to attend to, as his coins indicate that he began styling himself Persicus Maximus as of 310, a clear hint of a (very brief) war with the Persians. It is possible that he had won a minor victory over king Hormizd II, who died soon after and was succeeded by his son Shapur II, who was still an infant at the time. However this all may be, Daza seems to have sufficiently impressed Galerius to earn a promotion to augustus in 310.
In the west Constantine had largely ignored the decisions taken at the conference in Carnumtum. He had a strong power base in the western provinces, flat out rejected the title of filius augusti and continued to call himself augustus. Ultimately, in 310, he was also formally recognised as such. Furthermore, around 308 Constantine had become engaged in a war against the Germanic Bructeri. He managed to defeat them and then built a ship bridge across the Rhine at Colonia Claudia Ara Agrippinensium (Cologne) so that he could also control the other river bank. Subsequently he crossed the bridge for an expedition against the Franks.
Constantine and the gods
A much bigger challenge for Constantine was his father-in-law. Maximianus had settled at an estate near Arelate, but he certainly was not going spend his days in retirement there. On the contrary, the former emperor made plans to depose his son-in-law, presumably in 309. Among the troops stationed at Arelate he began spreading false rumours that Constantine had been killed in battle against the Franks. Large sums of money then quickly persuaded the men to proclaim Maximianus their new emperor. Constantine learned of the plot from Fausta, who chose loyalty to her husband over loyalty to her father. He immediately broke off his campaign against the Franks and advanced against his father-in-law. The latter left Arelate and withdrew to Massilia (Marseille), which was considered more defensible. After a brief siege, Maximianus surrendered. Perhaps Constantine had initially wanted to spare the old man who was, after all, his father-in-law. In the end, however, he had him strangled or forced him to commit suicide. This wily old fox was simply too dangerous.
After dealing with his father-in-law, Constantine returned to the Rhine to fight the Franks. On the way back to the front he presumably visited the sanctuary of Apollo Grannus at Andesina (Grand). Grannus was a Roman-Celtic deity associated with both the sun and water. The Romans equated him with Apollo. As evidence for Constantine’s visit to the sanctuary historians generally cite a panegyric (panegyricus), recited for the emperor by an orator in Augusta Treverorum in 310. At the time Constantine was celebrating his Quinquennalia there, his fifth year on the throne. The orator declared that Constantine “left the main road to visit the most beautiful temple – templum toto orbe pulcherrimum – in the whole world”. There Apollo and Victoria, the goddess of victory, were said to have appeared to the emperor. Although the panegyric does not actually say so, it is generally assumed that the aforementioned Apollo was none other than Apollo Grannus, so it must be concluded that Constantine left the main road in Gaul, running north-south, to visit Andesina. There he subsequently had a vision of the god, or – alternatively – saw him in a dream.
The only way the orator could have known that Constantine had seen Apollo was that the emperor had told him so. It is also possible that he had heard it from people in Constantine’s entourage. The panegyric continues: “But why do I say ‘I believe’. You HAVE seen him [Apollo] and you have recognised yourself in the image of Him who would rightfully gain control of the whole world”. It is obviously no longer possible to establish whether Constantine really had a vision or dream, or whether he simply made it up for political reasons. Judging by his coins, between 306 and 310 the emperor had mostly worshipped the gods Hercules and Mars. Hercules, of course, was the main god of the Herculii, a family line that Constantine represented within the Tetrarchy and that had been started by his father-in-law Maximianus. However, in 310 he had broken with both Maximianus and Hercules, trading in the latter for Sol Invictus, the Unconquered Sun. In Apollo Grannus he must have seen a manifestation of the Sun. Constantine continued to mint bronze coins with images of Sol until 318 and gold coins until 325. This is often seen as evidence that Constantine did not side with the Christians until after 325.
- Anonymus Valesianus, Origo Constantini Imperatoris 9;
- Aurelius Victor, De Caesaribus 40 (translated and annotated by H.W. Bird);
- Epitome de Caesaribus 39-40;
- Eutropius, Breviarium Historiae Romanae 10.1-10.4;
- Lactantius, De mortibus persecutorum, chapters XXVI-XXVII;
- Zosimus, Historia Nova, Book 2.
- Adrian Goldsworthy, The Fall of the West, p. 175-177 and p. 181;
- Henk Singor, Constantijn, p. 211-236;
- Timothy Venning, A Chronology of the Roman Empire, p. 638-642.
 Zosimus, Historia Nova, Book 2.9.
 Fausta was the daughter of Maximianus and Eutropia. Constantine’s father Constantius had been married to Theodora, a daughter of Eutropia and her first husband Hannibalianus, which made her Maximianus’ stepdaughter.
 According to the Epitome de Caesaribus 40, 3 and the Origo Constantini Imperatoris 4.10.
 Epitome de Caesaribus 39.5.
 Henk Singor, Constantijn, p. 233.
 “De enige keizer die het conflict als een werkelijk religieus conflict zag”, Henk Singor, Constantijn, p. 211.
 My translation into English from the Dutch translation in Henk Singor, Constantijn, p. 231.
 See the Dutch translation in Singor, p. 232.