DIOCLETIAN HAD DECIDED TO open the celebration of his twentieth year in power, or vicennalia, in November of 303 at Rome. It would be the first time in a decade that he would meet with Maximian in person. The encounter would be a moment of symbolic significance, as the two self-proclaimed saviors of the Roman world appeared together before the people of the city which, although no longer an imperial capital, was still very much felt to be the heart of the empire. And so it might also have been a suitable place, deep inside the territory of Maximian, for Diocletian to stage one last demonstration of his superior authority. He had come to Rome not only to celebrate the anniversary but also to gain Maximian’s agreement to a definitive plan for the succession.
It had been clear for some time that Diocletian did not intend to die in office—that was the point of the retirement palace being built in Split and explained the absence of a tomb in a capital like Nicomedia (Roman emperors had a tendency, when they could, to make elaborate preparations for their burial). It was even admitted by a source hostile to the abdication scheme that Diocletian and Maximian had both planned on retirement.1
Despite strong claims Lactantius would put forward at a later date that Constantine was seen by all as an obvious candidate for Caesar, there is no evidence that this was ever in prospect. Lactantius’ assertions do not appear in other pro-Constantinian sources, including a series of top-level speeches delivered during the next decade. Moreover, the fact Constantius was married to Theodora, Maximian’s step-daughter, and Galerius to Diocletian’s daughter Valeria, and that Galerius’ own daughters were married to Maxentius, the elder son of Maximian, and to a soldier named Maximinus all more than suggest that marriage was a marker for potential promotion. Constantine was outside the charmed circle.
Although Galerius did not force the removal of Constantine from the line of succession, there is reason to believe that he pressured Diocletian into arranging the retirement of the Augusti in the wake of the vicennalia celebration.2 It was on this occasion that Maximian and Diocletian confirmed the agreement at a meeting in the temple of Capitoline Jupiter, quite possibly setting May 1, 305, as the date so that Maximian could enjoy a final blaze of glory when he presided over the ludi saeculares; scheduled for 304, these would commemorate the one-thousandth anniversary of the foundation of Rome according to the calculation used by Septimius Severus. While there is some corroboration for the idea that abdication had long been in view, there is more to suggest a sudden change in the way it would work. It is striking that, as mentioned earlier, the count of Maximian’s regnal years was changed in 303 so that they suddenly equaled those of Diocletian. There would have been no point in the change except to disguise the fact that he had held power for one year less than his colleague.
Also striking is other evidence, from coins, suggesting that important decisions were being made in the east without prior consultation with the west. The mint at Trier, for instance, produced coins in 303 for Diocletian announcing the fulfilment of vows taken the previous decade, and also prospective vows for the next one. The mint at Nicomedia issued no such coins, suggesting that the mint master there had gotten the word well in advance of his counterpart at Trier that there would be no thirtieth year.3
The crucial evidence that something dubious was going on both in the timing of the abdication and the choice of successors lies in the events of the next few years. While we can’t know whether the new Caesars to succeed Constantius and Galerius, Severus and Maximinus Daia, were selected in 303, we can be quite sure that neither of the successors was close to Maximian and Constantius. Both were friends of Galerius; and while one, Maximinus, was Galerius’ son-in-law, neither had yet occupied a top-level appointment.4 We also know that Constantius was no friend to the new arrangement. There were some immediate and major changes in the empire’s administrative structure after the abdications that reflect the tension of the times.
We have little information about the period between December 20, 303, when Diocletian left Rome for the last time, evidently suffering from a serious illness, and May 1, 305. Probably after spending some time at Ravenna he returned to the Danube, where he took command in Galerius’ company of a campaign against a Germanic tribe called the Carpi. He reached Nicomedia by August 28 that year and appears to have remained near his capital after that. Maximian apparently left Rome almost immediately after Diocletian did and went to Sirmium, where Lactantius claims he had a stormy meeting with Galerius.5
When May 1, 305, dawned, Constantius and Maximian were ensconced at Milan, while Galerius and Diocletian were at Nicomedia. In both places, the same drama was to unfold, one that had no parallel in earlier Roman history. Diocletian went out to a high platform built on the spot where he had, twenty-one years before, addressed the army and received its acclamation as emperor. The place was well marked with a high column upon which there was a statue of Jupiter. He would have been resplendent in his purple robes and jewels as he sat in the cart that bore him to the site. All around him would have been members of the court, soldiers invited from throughout the empire to witness the event. When members of the platform party had taken their places—Constantine was a member of this group—the senior emperor came forward to speak. He was old, so he said, he was tired, he wished to rest from his labors and so he would now pass power to others. The new Caesars, Severus and Maximinus, were announced though Severus was far away that day, in Milan, where he was participating in a similar ceremony with Maximian and Constantius. The chief actor in Nicomedia was Galerius, who brought Maximinus forward to face Diocletian. Diocletian removed the purple cloak from around his shoulders. He placed it on Maximinus. In so doing he ceased to be emperor. One can only imagine what it was to witness this—tens of thousands must have held their breath while the act took place. Then they would have exploded into acclamations of the new Augustus, Galerius, and the new Caesar. The man who had recently been the most powerful human anyone there had ever seen walked off the platform, remounted his cart, and was carried back to Nicomedia. Shortly thereafter he set out for Split, to enjoy a life of ease in his new palace.6
Never before had a man at the height of his power voluntarily laid that power aside, exploiting the very symbols that he had made those of the imperial office. There is perhaps no more powerful expression of the surprise that gripped the empire when news of the two abdications spread than the text of an inscription from North Africa honoring “our Lords Diocletian and Maximian the senior Augusti, and our Lords Constantius and Maximianus (Galerius) the invincible Augusti and Severus and Maximinus the most noble Caesars.”7 With the ceremony of May 1, Diocletian and Maximian had ceased to be lords of anyone or anywhere.
Diocletian chose his troops as the audience for his abdication, for he hoped it would be the army that would guarantee the new order. At Milan, Maximian took off his purple cloak and handed it to Severus, while proclaiming Constantius Augustus.8
Diocletian’s hopes for the army would prove ill founded: it would soon become clear that, so far from uniting behind the college of Caesars, it would prefer to distribute its loyalties between them.
Constantine’s impression of that day would emerge over time. He would never build a retirement palace. He preferred to die in office. Retirement was one act of Diocletian’s he could never hope to match.