One hundred and forty two years separate the accession of emperor Diocletian in 284 CE from the accession of the emperor Valentinian III in 425 CE. Of these one hundred and forty two years, forty-eight saw civil wars between rival emperors that pitted the resources and soldiers of one part of the Roman Empire against another in mortal competition for the imperial succession. That is to say, for more than one in every three years during this crucial century and a half, the Roman Empire was riven by civil war. Of the fifty-four men who claimed the title of Augustus during this period, thirty-nine of them – almost three quarters – died at the hands of their fellow Romans. They fell in battle against Roman armies, were assassinated or executed by a rival emperor, or committed suicide when all other options had been exhausted. Of these fifty-four Augusti, modern historians deem barely more than one third ‘legitimate’ emperors. The others are variously designated ‘usurpers’, ‘pretenders’, or simply ‘failures’.
It would not be a mischaracterisation or an exaggeration to say that the late Roman state was a polity defined by civil war. Roman leaders at this time approached their rule ever cognizant of the fact that sooner or later one of their subordinates could don the purple robe, stand before a provincial army, and be proclaimed emperor. The precariousness of all claims to power shaped the way emperors organized their military, interacted with their subjects, presented their court, appointed officials, imposed discipline, and even distributed money. Once a usurper arose, the machinery of civil warfare would again grind into action. Only the death of one or other emperor could bring it to a halt.
Given this, it is perhaps surprising that a history of usurpation and civil war in the later Empire has never been written (at least not in English). Indeed, on occasion, it can seem as if the topic is being specifically avoided. If this is so, however, then modern scholars are following in a grand old tradition that goes right back to the Roman period, for to speak of usurpation and civil war – in other words, for a Roman author to speak of the enemies of the emperor under whom he lived – was a dangerous and a difficult thing. When an emperor fell from power, his conqueror would subject him to the processes sanction against memory that we today know by the name of damnatio memoriae. His statues would be mutilated and toppled, his inscriptions erased, his laws cancelled, his adherents rounded up and executed, his name removed from public records and the offices, titles, and privileges he had granted would be declared void. So long as the conqueror – or his dynasty – lived to perpetuate the memory of the usurper’s defeat, to praise the fallen would be a capital offense. Thus, the history of the late Roman state becomes a series of officially sanctioned narratives from which no wise author would dare to dissent.
This injunction of silence – ‘let that time be regarded as if it never was’, as a law of Honorius’ from 395 has it – was designed to designate fallen emperors as the perpetrators of a crime so heinous that its name could not even be spoken. For the historian, its effect has been to veil the history of this period with silence and destroy sources that would otherwise allow us to reconstruct the lives and reigns of the men who failed in the terrible competition to rule the late Roman state. As the fourth-century biographer of the second-century usurper Pescennius Niger put it, ‘it is an unusual thing, and a difficult one, to set fairly in writing the deeds of those made tyrants by the victory of others.’
It is into this world of constant violent competition over the imperial title, and of the aggressive suppression of dissenting narratives, that my book Emperors and Usurpers in the Later Roman Empire steps. The book seeks to shine a light on the processes that led to one man becoming an emperor and another becoming a tyrant. To understand them, I turn to the ceremony of the imperial court, and to one particular source above all: panegyric. Like no other medium in the late Roman world, panegyric was intimately concerned with the business of civil war and usurpation. Of the nearly fifty surviving prose panegyrics delivered in the century between 289 and 389 AD, more than one third record the events of a civil war in which their emperor was a participant (and because of the nature of our evidence, a victor). These speeches recount, in intricate detail, the supposedly taboo events of the bloody conflicts that their emperor waged against his enemies, painting defeated usurpers in lurid caricature – they are drunkards, they are lechers, they are cowards, they are impious; they are barbarians, they are pirates, they are tyrants; they fill their cities with Roman dead and their coffers with stolen gold. In the panegyrics we find, in triumphant opposition to the notional silence of the damnatio memoriae, a cacophony of public rhetoric (supported by ceremonial building and imperial display) that endlessly commemorated and recycled the narratives of civil wars fought and won as part of a process whereby emperors legitimated themselves and the violence they had wrought on the Roman world.
The invectives of the panegyric were not undifferentiated barrages of abuse, however, and in the book I explore in detail how the regimes of fallen emperors were commemorated throughout the territories of victorious emperors in calculated, targets ways. Panegyrics took the public face of fallen emperors, the image they had displayed to the world, and purposefully subverted it so that it became a stick with which to beat them. Examples of these characterizations abound within this literature. The naval captain Carausius, whose British Empire was for so long protected by the bulwark of the English Channel, became a rapacious pirate. The imperial prince turned emperor, Maxentius, who reversed the tetrarchic abandonment of Rome, made his home there, and lavished on the capital a rich programme of building unlike anything bestowed upon the city for generations was memorialized as a frivolous weakling who filled the Tiber’s water with butchered senators. The hardy, career soldier, Magnentius, whose rebellion overthrew the ineffectual government of the emperor Constans became, to the panegyrists of Constantius, a wild barbarian addled with drink and inconstant to his core. These were targeted messages, which bit at the heart of what these fallen emperors had each attempted to do with their tenure of the imperial office. In studying these rhetorical characterizations we see the concerns that animated both fallen usurper and conquering emperor.
What we see above all, however, is that the reach of the panegyrics was exceptionally long. In my book, I argue for panegyric’s ubiquity in the Roman world. Roman historians very famously brought their histories to a conclusion before the beginning of the reign of the emperor under whom they wrote, and when they did so they often explicitly yielded the floor to panegyric (think of Ammianus’ famous procudere linguas ad maiores moneo stilos). Panegyric was the only proper medium in which to deal with a living emperor’s reign, since a historian who subjected a living emperor to the impartial scrutiny of history might as well write out his death warrant at the same time. What this means is that, though panegyric was first and foremost an oral medium, the texts of panegyrics were, for years or even decades, the only written histories of a given emperor’s reign that existed. When that emperor died they would thus become one of the key primary sources with which the historian would seek to build their own narratives. Though ancient historians, like modern ones, were not thoughtless slaves to their sources (at least not always), nonetheless the messages and narratives of panegyric exerted an enormous influence on the way history was recorded and on how fallen usurpers were remembered. The slurs and stories of the panegyrics are to be found woven throughout the works of later historians, an unnerving seam of politically motived invective running through the sources upon which we most rely for our understanding of the past. Even Ammianus, Edward Gibbon’s ‘accurate and faithful guide’, is not innocent of this charge.
Through examination of these issues, this book becomes more than simply a study of the history of the later Roman Empire’s civil wars. In considering the contradictions and the historical processes that led to one man being made a tyrant by the victory of another, this book becomes an examination of the very ideological basis of imperial power itself, and explores what it is we mean when we call an emperor ‘legitimate’. It argues that the very idea of ‘legitimacy’, if couched in modern, legalistic, constitutional terms, is wholly alien to the institution of the Roman imperial office. The later Roman Empire had reached a crisis of legitimacy, in which the imperial office was now so readily grasped at by claimants and pretenders that each successive emperor – most of them claimants and pretenders themselves – needed to publicly and aggressively articulate their legitimacy as a moral force ranged in opposition to the evils of tyranny and despotism which they had defeated. In this world the maxim that victors wrote history became explicitly linked to the process of legitimation, for it was through their victories over their rivals that late Roman emperors presented themselves as fit to rule. Thus the great dichotomy of Emperors and Usurpers: it was usurpers, in some sense, who made emperors, for by the overthrow of all opposition an emperor demonstrated himself chosen to rule.
 See, for example, the lists provided in D. Kienast, Römische Kaisertabelle: Grundzüge einer römischen Kaiserchronogie (Darmstadt, 1996).
 CTh. XV.14.9.
 HA Pesc. Nig. 1.1-2.
 A medium perhaps unfamiliar to those who do not study societies in which it was employed, panegyric was a genre of formal oratory associated with the intense praise of (usually) a living individual. It was a form developed in the Greek world that rose to particular prominence under the Roman Empire, thanks to its suitability for the absolute monarchy that the Romans created. Cf. Nixon, C. E. V., and Rodgers, B. S. (ed. and tr.), In Praise of Later Roman Emperors: the Panegyrici Latini (Berkeley, CA, 1994); M. Whitby (ed.), The Propaganda of Power: The Role of Panegyric in Late Antiquity (Leiden, 1998); Heather, P. J., and Moncur, D. (tr.), Politics, Philosophy, and Empire in the Fourth Century: Select Orations of Themistius (Translated Texts for Historians 36. Liverpool, 2001).
 Amm., XXXI.16.9. These were the closing words to Ammianus’ history of his times: ‘As for the rest, let it be written by better men, in the flower of their youth and their learning. I would warn such men, however, if it please them, to advance in this task by forging their language to the higher style [i. e. panegyric].’
 Cf. G. Sabbah, La méthode d’Ammien Marcellin: recherches surlaconstruction du discours historique dans les Res Gestae (Paris, 1978), 332-46 and M. Humphries ‘Nec metu nec adulandi foeditate constricta: The image of Valentinian I from Symmachus to Ammianus,’ in J. W. Drijvers and D. Hunt (eds.) The Late Roman World and its Historian: Interpreting Ammianus Marcellinus (London, 1999), 117-26.
Adrastos Omissi is Lecturer in Latin Literature at the University of Glasgow. This post was adapted from his new book, Emperors and Usurpers in the Later Roman Empire (Oxford University Press, 2018).