The Roman emperorship was a bizarre and unique office. Its creators and most of its earliest occupants insisted that it was not an office at all, and certainly not a monarchic one. There was no agreement in antiquity about when precisely it began, and no consensus even among scholars today about when it may be said to have ended. Virtually everything about it was formally undefined, from its legal powers to the criteria which permitted it be transferred or assumed. Even its name varied situationally, and the choice to use any of Augustus, Caesar, imperator, princeps, autokrator, basileus or any of myriad other possibilities was one laden with subtext and consequence. Caesar Rules sets itself the ambitious challenge of filling the hole left by this acknowledged absence of definition by reconstructing how the Roman emperor was perceived and defined by those around him, in particular through their expectations of him. In this excellent volume, Olivier Hekster is remarkably successful at producing a sweeping, well-argued and engaging analysis which should provide an indispensable starting point for future studies on this most unusual position.
The volume’s subtitle immediately places it in conversation with Fergus Millar’s classic 1977 work, The Emperor in the Roman World. Millar dealt the ambiguity of the Roman emperorship by offering a predominantly positivistic approach that brought together the reports of ancient texts on the emperor’s setting, function, and legal relationships. His emphasis was above all on the emperor’s role as a judge and lawgiver, summarized in his famous dictum that ‘the emperor was what the emperor did’ (Millar, p. 6). Despite the connotations of his title however, Hekster neither continues Millar’s tradition nor explicitly critiques him, mentioning his most famous work only to praise its immense contribution to our understanding of the emperor’s civic role in the Roman imagination (p. 160). Yet it is telling that Hekster concludes his brief discussion of The Emperor in the Roman World by noting that this civic role was ‘only part of the story’.
In spite of the lack of overt challenge, Hekster’s work in fact represents a dramatic break from Millar’s approach. Part of this is captured in the additional adjective ‘changing’ in this volume’s title. Millar’s emperor is effectively static, performing the same bureaucratic functions at Rome and at Constantinople. In contrast, one of Hekster’s primary concerns is to lay out the patterns of continuity and evolution that fluctuated unceasingly in the ‘changing’ Roman world—a world that is expanded for two centuries beyond Millar’s Constantinian terminus. This expanded perspective goes well beyond chronological reach, with Hekster also engaging far more fully with non-literary evidence including coins, inscriptions, art, and archaeology, as well as looking at aspects of the office neglected by Millar such as military and religious duties. Most fundamentally, Hekster follows prominent recent scholars such as Ando and Noreña in moving sharply away from Millar’s empiricist vision of the emperorship in favour of normative analysis grounded in ideals and perceptions. His Roman emperor is defined not only by what he ‘did’ but also by who was around him, where he was, and above all how he was seen by others.
It is the latter issue in particular which constitutes much of Hekster’s focus and provides the core of his central argument as laid out in the introduction: namely that the image and behaviour of the emperor were both shaped above all by the changing expectations of his subjects. These expectations led to the development of specific imperial roles that are organized here into three categories: military, religious, and civic. As Hekster emphasizes throughout, popular expectations for the emperor were then continually reshaped in response both to external events and to the models presented by the emperors themselves. Even unsuccessful rulers often helped to shift the boundaries of what was and was not an acceptable means of imperatorial representation. In this way, both emperors and subjects were engaged in a perpetual dialogue from the time of Augustus through to that of Justinian, with each new development in their relationship always framed by and responding to what had come before.
The first chapter is both the densest and most interesting of the volume. In it, Hekster explores the public portrayal of the emperor by looking at his titulature (in both ‘official’ and unofficial sources) and his representation in portraits, reliefs, and coins, as well as the visual signifiers of emperorship: clothing, crown, and sceptre. The chapter crisply synthesizes a vast range of evidence spanning literature, epigraphy, numismatics, and art to draw out broader patterns and their evolution over time and across regions. It is notably successful in challenging scholarly paradigms often taken for granted, such as the distinction between ‘official’ and ‘unofficial’ names, persuasively arguing that diverse onomastic representations of the emperor should be seen as the products of a process of negotiation rather than the imposition of a top-down model (p. 44). A set of graphs showing trends in numismatic representation add a welcome quantitative element to the case, appropriately with caveats throughout. Hekster convincingly demonstrates that the name ‘Augustus’ was perhaps the only element of the emperor’s image to remain unchanged throughout the period.
Chapter 2 on playing imperial roles covers more familiar ground, but the territory is indispensable to the volume’s underlying thesis. Hekster discusses the responsibilities which the emperor was expected to fulfill in the military, religious and civic spheres and how these were affected by changes in the historical context. Although the discussion of how the emperor’s religious role changed in response to Christianity is (perhaps unavoidably) compressed, the section on civic representation is a useful corrective to the idea that the emperor was seen primarily as a lawgiver. In fact, as the chapter demonstrates, he advertised himself in this capacity surprisingly rarely and only in select venues and to limited audiences. The final discussion on the role of exemplarity usefully recontextualizes these roles within the framework of expectations, noting the way that collective memory could reshape these with each new ruler.
Chapter 3 looks beyond the emperor himself to the men and women around him. A highlight of this chapter is the examination of the role of senators and bishops, whom Hekster argues can be considered similar (though hardly identical) actors in certain respects due to their membership of elite institutions with their own collective identities and interests that had unique relationships with the emperor. The roles of the court and the imperial family are also fully explored with the book’s typical and highly effective blend of textual and visual evidence. Hekster’s ability to move fluidly from detailed discussions of Julio-Claudian dynastic politics to the nuances of fifth-century Christian empresses serves as both a reminder of the essential continuity of Roman imperial history and an endorsement of his choice to embrace such a broad scope.
The fourth and final chapter interrogates the emperor’s spatial relationships and his interaction with both his capital(s) and the provinces. In line with the book’s chronological breadth, attention is paid to both Rome and Constantinople, from the impact of their distinctive urban geographies to the different possibilities which each metropolis presented to emperors for interacting with their subjects. Once again, even familiar material is compellingly resituated within the book’s framework of expectations and negotiated relationships. The completeness of the argument might have benefitted from more attention being paid to the significant period after the early third century but before the founding of Constantinople during which emperors were unmoored from any fixed residence.
Indeed, while the volume’s focus is expansive enough that it feels somewhat churlish to highlight rare omissions, Hekster does have a tendency to glide from the rule of the early Princeps who resided mostly at Rome to that of the late antique sedentary emperor, especially the eastern Augustus at Constantinople. Although considerable evidence from the long third century is fully integrated, some of the deeper changes to the emperorship in this period are thus elided or given comparatively little attention, particularly if they proved temporary. The most notable of these is the entire issue of Mehrkaisertum, multi-emperor rule, the norm for a significant span of the period under consideration (such as the overwhelming majority of the years between 250 and 480, with precedents in the second century). The existence of several men simultaneously performing the role of emperor was clearly an enormous shift in the history of an office formerly defined by its singular nature. Did this affect what the Romans expected from their emperors? Did it indeed represent a shift in response to those expectations, ensuring there was always greater proximity between ruler and ruled? Did the proliferation of emperors diminish their standing in the eyes of their subjects? Even establishing that the multiplication of the emperorship had no significant impact on the imperial image would be an important point in favour of the representational flexibility which Hekster emphasizes throughout. It is disappointing that questions so directly relevant to the central thesis of the work receive no real discussion here. Yet it must be stressed again that this is a rare silence in a work otherwise distinguished by its impressively comprehensive nature.
The book is meticulously researched and attractively presented. Images are plentiful, well-selected, and extremely helpful given the emphasis on material culture, as are the dynastic trees presented in the appendices. The use of visually clear graphs to trace long-term patterns is especially appreciated. More information on the datasets behind them might have been useful given the subjective nature of some of the criteria, but this concern is mitigated by the author’s laudable caution in presenting their results as useful general indicators rather than relying on them to prove specific points. The careful integration of text, images and data further reinforces the strength of the book’s central arguments.
Overall, Hekster does an admirable job of covering a truly impressive range in almost every aspect of his subject matter, from the materials consulted to the topics considered. As this volume demonstrates, the most powerful office in the ancient world was also its most ambiguous, its holder capable of both appearing and behaving in utterly different ways to different constituencies at different moments in imperial history. Caesar Rules fully embraces all of these contradictions with nuance and insight, and as a result stands as one of the definitive modern studies on the Roman emperorship.
 Millar, F. 1977: The Emperor in the Roman World (31 BC – AD 337), London (2nd ed., 1992, with a new Afterword).
 Ando, C. 2000: Imperial Ideology and the Provincial Loyalty in the Roman Empire, Berkeley; and Noreña, C. 2011: Imperial Ideals in the Roman West: Representation, Circulation, Power, Cambridge.
 In this, Hekster is also following the critique of Keith Hopkins in his influential review of Millar: Hopkins, K. 1978: ‘Rules of Evidence’, Journal of Roman Studies, 68, 178-186.
 The court has been a particular focus of much recent scholarship, including the forthcoming Davenport, C. & M. McEvoy, 2024: The Roman Imperial Court in the Principate and Late Antiquity, Oxford, and Kelly, B. and A. Hug, 2022: The Roman Emperor and his Court, Cambridge, with Hekster contributing directly to the latter project.
 See for example Mayer, E. 2002: Rom ist dort, wo der Kaiser ist. Untersuchungen zu den Staatsdenkmälern des dezentralisierten Reiches von Diocletian bis zu Theodosius II, Mainz.