On 18 January 350, the flag of revolt was raised at Autun in central Gaul. At a dinner party, a cadre of disgruntled (disgruntled about what exactly is another subject altogether…) military officers and civilian officials declared Flavius Magnus Magnentius, commander of the Herculiani and Ioviani imperial guard units, emperor in opposition to Constans (Zosimus II.42.2-5; Julian, Or. II.57d-58a; [Aur. Vic.] Epit. XLI.22; Chr. Min. I.237; Jerome, Chron. 237.). While more a desperate plot mounted by officials fearful of losing their positions than a well-orchestrated revolt against an unpopular emperor, the usurpation of Magnentius benefited greatly from good timing. Constans was on a hunting trip in the foothills of the Pyrenees, detached from the safety of his supporters, allowing the rebels to corner and murder him ([Aur. Vic.], Epit. XLI.23; Aur. Vic. de Caes. XLI.21.23; Zosimus II.41-42; Ammianus XV.5.17).
With one emperor disposed of, Magnentius moved quickly to assert his new found authority. He had installed an ally as praefectus urbi at Rome by 27 February and Aquileia was minting his coins by early March (RIC VIII.325/6 Aquileia 122). After adding the important province to Africa, the usurper seemed set to role up the rest of Europe before Constans’ older brother, Constantius II, could detach himself from the eastern frontier. However, the passes through the Julian Alps into Illyricum was as far as Magnentius was to get. This was because on 1 March, the Illyrian armies had proclaimed their own emperor, the Moesian magister peditum, Vetranio. Little is known of his early life, but Vetranio is likely to have enlisted when he was young and then served dutifully and successfully, rising up through the ranks through his ability to be in a position to serve as Constans’ ‘master of infantry’ in Illyricum. In his new imperial postion, Vetranio quickly bolstered the forces under his command with recruiting and distribution of an accession bonus, minting his own coins (some of which were minted so quickly that they did not notice that the new emperor’s name was misspelled – VERTANIO).
The opposition of Vetranio’s Illyrian field army and a distraction of another revolt in Rome – that of Nepotianus – not only halted Magnentius’ progress east, but probably put paid to the long-term aims and ultimately the survival of his usurpation. By not being able to oust Vetranio and gain access to the vital manpower of the Balkans, Magnentius could not expect to be able to force Constantius into accepting him as his imperial colleague. While Constantius was displayed on Magnentian coins, this was likely a fool’s errand from the very start as Constantius was not one to allow the usurping of his family’s position. Any lasting notion of accommodation ended when Constantius rejected any type of alliance. By mid-summer 350, the usurpation of Magnentius was only going to be decided by a battlefield encounter between the forces of the Gallic usurper and the eastern forces of Constantius II.
But what of the Illyrian field army? What of Vetranio? While the historical record is scant, it is likely that he spent the second half of 350 consolidating his position in the Balkans and keeping a wary eye on the forces of Magnentius, who had not given up on forcing his way into Illyricum. However, Vetranio should perhaps have been looking the other direction… Fighting on the eastern front had ended for the year and by mid-December, Constantius II had arrived at Serdica with the eastern field army (Zonaras XIII.7).
The Balkan usurper quickly moved to intercept the emperor, but it was right on the eve of this presumed battle between the forces of Illyria and the east that something curious occurred. Rather than fight it out, Constantius and Vetranio met in person and on Christmas Day, they appeared together before the assembled troops at Naissus. There, rather than announce some co-operation against Magnentius, Constantius addressed the soldiers, who then acclaimed him as imperator. He then invited Vetranio to relinquish his imperial title and command of the Illyrian forces, which he agreed to. Constantius then magnanimously invited Vetranio to share his table for a grand meal, referring to him as ‘father’, before packing him off to a peaceful retirement at Prusa in Bithynia, where he lived on a generous pension until his death in 356 (Jerome, Chron. 238; Chr. Min. I.238; Zosimus II.44.3-4; Philostorgius III.22).
Just what exactly went on, not just here at Christmas 350, but throughout the entire year with regards to the usurpation of Vetranio. There are enough holes in the historical record for there to be a considerable number of plausible explanations. It could just be that the entire usurpation of Vetranio played out no differently than many others – a powerful general takes advantage of a power vacuum, in this case the murder of Constans and the absence of Constantius II, and has his men declare him emperor. It had happened with alarming regularity throughout the third century, so for it to reappear as soon as there seemed to be some decline in the authority of the Constantinian dynasty would not be surprising.
However, this would not explain the fizzling out of the usurpation at Christmas 350. It could just be that Vetranio was taken by surprise at the alacrity of Constantius’ arrival in the Balkans at the head of a battle-hardened field army, but then he had been in contact with Constantius over the course of the previous months, so total surprise would seem unlikely. Perhaps the usurper was unwilling to risk his own life in a battle against an emperor with a strong military reputation and imperial pedigree. Or perhaps it was his own Illyrian soldiers who demonstrated a similar unwillingness to fight the only legitimate emperor and member of the Constantinian dynasty. Vetranio being pressed into submission by his own troops as well as the presence of Constantius and his eastern army would explain the meeting at Serdica and what seems like a combined, military assembly of Illyrian and eastern forces at Naissus. Neither of these would seem likely had war between Vetranio and Constantius still been in the offing by December 350.
Perhaps instead of being surprised by Constantius’ speedy arrival, Vetranio was taken unawares by something else – Constantius’ cunning and rhetorical ability. If Vetranio was expecting Constantius’ arrival in the Balkans and with reports of him sending repeated calls for financial and military aid in fighting Magnentius, on top of his professions of loyalty to Constantius, it could be that the meeting in Serdica, away from the pressurising presence of their armies, was a scheduled one between military allies. Certainly, whatever his reasons, Constantius had shown willingness to accept Vetranio’s elevation, having sent him a diadem, money and charge of the troops on the Danube.
Together at Serdica, they may have planned out their joint move against Magnentius, possibly leaving the prickly issues of what to do with the division of power diplomatically unaddressed. They then returned to their armies at Naissus and appeared before an assembly of both Illyrian and eastern field armies to announce the fruits of their planning session. It may have all seemed like a functioning military alliance. This was until Constantius II took to the podium first. As senior emperor, this will have been his prerogative and he took full advantage of it, delivering a Christmas Day message to remember. Perhaps rather than lay out any plan expected by the an acquiescent-looking Vetranio beside him, Constantius used his not inconsiderable rhetorical skills, his own military reputation and his Constantinian heritage to gain the allegiance of the Illyrian forces.
However, would Constantius have really have mounted the podium at Naissus relying on his own rhetorical skills and dynastic heritage to sway the Illyrian troops over to his side? Surely a pragmatic emperor like Constantius would only have put himself in that position if he felt that the result was a foregone conclusion. This would imply that he had foreknowledge of the outcome, either due to a pre-arranged agreement with Vetranio or perhaps through a successful bribing of the leaders of the Illyrian field forces (Bleckmann (1994), 53).
In either light, the public invitation for Vetranio to relinquish the imperial purple was more a public stripping of office. The Moesian general may have been merely unable to say no in the face of the soliderly support for Constantine the Great’s last remaining son and his own out-manoeuvring when Constantius presented to the crowd that Vetranio had agreed to give up his imperial position for the good of the empire.
The question must be asked would Constantius have treated an out-manoeuvred usurper as well as he treated Vetranio? It could be that Constantius felt thankful for Vetranio’s intervention in the Balkans as a buffer to Magnentius and then his peaceful acceptance of his deposition. It kept the manpower of Illyricum from the western usurper and ultimately delivered it to Constantius without the need for a potentially costly conflict. However, Constantius does not seem like the kind of man to forget such a slight against, never mind usurping of, his imperial dignity.
There is also some evidence that Vetranio may not have been the completely compliant supporter of Constantius he tried to make himself out to be in his coins and letters to the emperor. Philostorgius would have it that Constantius, initially planning to ally with the Illyrian usurper against Magnentius, seized Vetranio and had him divested of his imperial office “since the latter showed signs of rebelling,” (Philotorgius III.22) which could be linked to Vetranio’s moves to secure the passes between his forces and those of Constantius (perhaps evidence of Vetranio’s lack of trust in Constantius?; Philotorgius III.24). Vetranio had also shown a willingness to negotiate with Magnentius, sending a delegation to him and perhaps had even come to terms with him (Zosimus II.44.2; Julian, Or. I.30B-33C, possibly encouraged to do so by his ‘young men’ (Or. II.76C)). He may even have sent a joint delegation with Magnentius to Constantius, which urged the emperor to be satisfied with primacy amongst the three Augusti (Petrus Patricius, Excerpta de Legationibus 14; Zonaras XIII.7.15-28).
If Constantius was in any doubt over Vetranio’s allegiance, his treatment of the deposed usurper would seem at odds with the lack of clemency he showed towards others he doubted, including members of his own family. So why might a deposed usurper of no familial connection garner better treatment, even if he had been a valuable servant to the Constantinian dynasty? Certainly, the Illyrian army may have taken any punishment of their beloved commander badly at a time when Constantius needed them in his inevitable showdown with Magnentius. That might explain why Vetranio was initially allowed to retire in peace, but perhaps not why he was allowed to continue in his Bithynian retirement until his death. It could well be imagined that whatever the circumstances of Vetranio’s retirement, Constantius had his officials and spies keep an eye on the deposed usurper up until the day he died. Perhaps the reports Constantius received about Vetranio revealed him to bear no ill-will towards the emperor or his lot. He may even have continued to openly voice his support for Constantius. It could also be that Vetranio was not in the best of health by the time Constantius felt the need to punish the deposed usurper and so he left the aging general in peace for the rest of his days.
In Part II, we will look at the other major player in this fourth century Roman game of thrones: Constantius II's sister, Constantina.
Bibliography
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Blockley, R.C. ‘Constantius Gallus and Julian as Caesars of Constantius II’, Latomus 31 (1972) 431-468
Burgess, R. ‘The Summer of Blood: The “Great Massacre” of 337 and the Promotion of the Sons of Constantine’, DOP 62 (2008), 5-51
Crawford, P.T. Constantius II: Usurpers, Eunuchs and the Antichrist. Barnsley (2016)
Drinkwater, J.F. ‘The Revolt and Ethnicity of the usurper Magnentius (350-353) and the Rebellion of Vetranio (350)’, Chiron 30 (2000) 131-159
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