Interesting! Gives a good explanation for Valentinian's actions. The decision to leave Valens in the East does strike me as a little irresponsible on Valentinian's part. Valens had little in the way of experience and could easily have been overthrown by Procopius. Procopius had a lot of success winning over Constantinople and the soldiers of Thrace. His reverence for the Constantinian dynasty and the use of Constantius II's family was a good move. Had Procopius managed to bring over the veteran general Arbitio it might have been over for Valens.
I imagine Valentinian would then have had to go East and face Procopius?
Yeah, Drinkwater's theories, which do seem plausible, do not cast Valentinian in a great light. I suspect Valentinian would have continued to play things defensively, blocking the passes into Italy. Here is Drinkwater's theory on Valentinian re. Procopius (273-275):
'One might expect the new western emperor, who had already sought to establish his dominance over Alamanni and who needed to confirm his credentials as a soldier, to have taken immediate personal action (My note: against the Alemanni). But Valentinian sent out Dagalaifus. Moreover, when Dagalaifus then, and again in 366, proved unable to bring the Alamanni to heel and was recalled, he did not suffer for his failure but, on the contrary, was given the immense honour of being appointed consul with no less a colleague than Valentinian’s son and heir, Gratian. After Dagalaifus, Valentinian again failed to go himself to fight the Alamanni but, in 366, sent another of Julian’s old generals, Jovinus, who finally defeated them and was also honoured with a consulship. Jovinus’ victories may be dated after the west had received news of Procopius’ defeat. It is odd that Alamanni who were slippery and invincible during the rebellion were relatively easy to suppress afterwards.
The explanation for this strange run of events surely lies in its political context. Valentinian made much of Alamanni in announcing that he would not help Valens against Procopius. He is supposed to have been persuaded by his counsellors and deputations from the Gallic communities not to expose Gaul to barbarian attack by leaving the country, and to have reconciled himself to this difficult decision by appreciating that, while Procopius was merely the enemy of himself and his brother, the Alamanni were the enemies of the whole world. This is very suspect.
Valentinian’s prioritizing of the interests of the state over those of his family resembles the excuse given by Claudius II for not proceeding against the usurper Postumus in 268, and may be regarded as a convenient piece of moralizing. Symmachus, in a speech delivered early in 369, seems defensive about Valentinian’s early activities in Gaul, making him reach the Rhine quickly and (as Ammianus was to do in his turn) presenting the emperor’s refusal to help Valens as the sacrificing of personal pride to the public good. This suggests that the western court, realizing the sensitivity of the situation, took pains to put into circulation an old but reliable justification for Valentinian’s refusal to accept the obligations traditionally due to a blood relative. Valentinian had no intention of returning east; and to avoid such a return he and his counsellors exaggerated a series of minor frontier skirmishes. Again, this was made possible not because of what the Alamanni had recently done, or what they might do, but because of the image of them created in the 260s and 270s, and the 350s. Contrary to what he claimed, it is likely that the emperor’s mind was made up by his appreciation of the gravity of internal, not external, dangers.
Valentinian had to keep the western armies on his side. The revolt of Procopius will have shaken the new and untested dynasty. We need to visualize Procopius’ rebellion as it may have appeared when it was enjoying its early successes: not, as Ammianus would have it, the last gamble of a pathetic and unworthy successor to Julian, but the promising debut of the true heir, through his relationship with Julian and his association with Constantius II’s widow and daughter, to the throne of Constantine. It is no wonder that, as soon as was decently possible after the suppression of Procopius, Valentinian had Gratian marry Constantius II’s only child. In November 365, he must have thought twice about taking troops to the east, to be directly reminded of their Flavian loyalties.
In addition, he cannot have felt completely confident about his own position in the west, where memories of Julian and his achievements will have been especially strong. The western establishment’s ambivalence towards the new dynasty was to manifest itself in 367, when Valentinian’s illness provoked intense speculation as to a successor and led to the unprecedented promotion of Gratian directly to the rank of Augustus. In 365, precipitate departure from the west might compound the uncertainty caused by Procopius’ rebellion by signifying Valentinian’s lack of confidence in Valens’ ability to deal with the usurper… Events in the east were moving so quickly that Valentinian was unable to form a clear picture of what was happening: a reckless campaign might lead to his own defeat, or leave him the irreconcilable enemy of a renascent Flavian dynasty. His best course was to stay put and hold firm.'
