It is a commonly held view that the Romans prohibited their armies from entering the gates of their city, noting a clear divide between what should be considered domestic and martial. The pomerium, which was said to have dated back to Rome’s founding, marked that dividing line. Koortbojian’s study brilliantly parses the evidence, using both texts and images, to identify how the pomerium operated as a Roman concept, rather than just a physical boundary. In doing so, he challenges a number of common interpretations of the pomerium, including the idea that troops were not allowed within the city, and he attempts to illuminate how figures like Caesar, Augustus, and Constantine themselves challenged several conceptual norms over time.
The work opens with a brief introduction that serves as an overview of ancient historical narratives about the pomerium. Koortbojian looks at authors such as Livy, Tacitus, Plutarch, and Dionysius to outline how the idea of the pomerium had changed its boundaries since its initial creation, at least as its creation was presented in these authors. The introduction also notes how these later authors used their own reality to inform their understanding of early Rome. This is a common insight in scholarship today, often applied to things like the origins of priestly or political offices, but it remains useful when applied to the pomerium. It is also useful since the bulk of the study looks at evidence outside of these sorts of antiquarian sources, focusing more on the contemporary realities that informed them.
Chapter 1 begins with a review of the commonly understood reason for the existence of the pomerium, to serve as a conceptual marker between the city of Rome and the outside world. How that outside world was defined might have changed, as in the distinctions between city and field (urbs and ager) or at home and abroad (domi and militiae), but the pomerium always stood as that conceptual boundary. Much of the chapter focuses on this conceptual boundary and how it would be used by Caesar, Augustus, and others, via statuary and portraiture, in their attempts to amass or bolster power. Koortbojian’s attention is directed at Caesar’s now lost statua loricata, which likely became a precedent for Augustus, including the famous Prima Porta. Caesar seems to have used that statue as a display of his status as imperator, even while within the pomerium, thus crossing the conceptual boundary between the city and the campaign field.
Chapter 2 turns to the more religious aspects of the pomerium, primarily by looking at its role in the taking of public auspices and the importance of auspices in assuming command as magistrate or promagistrate. The primary figure of concern is Octavian, who had a special status, receiving imperium through non-standard means. The chapter begins with an overview of how imperium was usually conferred and how power required both legal and religious approval to be considered just. It also examines auspices that would be taken before important state actions were undertaken, such as a meeting of the senate. Koortbojian pushes back against the idea that Roman magistrates took special “auspices of departure” before leaving the city. Instead, he argues that these appear to be the usual auspices taken before undergoing any state action. He returns to Octavian near the end of the chapter to discuss private individuals taking public auspices since privati cum imperio were limited to taking auspices when they entered their provincia, unlike consuls who could take auspices both in the city and outside it. Octavian, of course, had special authority, and once the triumvirate was formed, he began consolidating his image to reflect both his imperium and right to take public auspices. This was one of the many ways he reinforced his authority at Rome, as Koortbojian stresses throughout this chapter.
Chapter 3 is a cogent chapter because it attempts, rather successfully, to further define Roman ritual (ritus Romanus) as opposed to, for example, Greek ritual (ritus Graecus). Our standard understanding of the Roman perception of Greek and Roman models of ritual is that Greeks performed theirs with their head uncovered (capite aperto), while Romans’ heads would be veiled (capite velato). Koortbojian demonstrates, primarily through numismatic and relief images, that Romans also performed rituals with uncovered heads, but they did so only in the military context, which he calls ritus militaris, usually also marked by the wearing of armor and paludamentum. Thus, the “standard Roman” model of ritual, with the head covered, is really a Roman civicsacrifice. Even if the ritual was performed outside the pomerium, as in the case of the lustratio exercitus, if it was civic in nature, it would be performed capite velato. In other words, it was performed with a covered head and not an uncovered head in paludamentum as one might expect in military contexts, despite the martial setting of the lustratio exercitus, since it was inherently a civic ritual following the model of Rome’s foundation. Koortbojian’s idea of ritus militaris reinforces an ideological distinction, not necessarily a geographical one, between actions taken domi or militiae, along the same lines as the conceptual meaning of the pomerium. It also adds a new axis to Roman religion so that it is no longer enough to describe “Roman ritual” as capite velato.
Chapter 4, the final chapter, provides a close look at the creation of Constantine’s arch, its imagery, and the ideas that such imagery conveyed, including the phrase triumphis insignem. Koortbojian challenges a number of standard views about the arch, primarily that: 1) it displays Constantine’s triumph after defeating Maxentius and 2) even though a triumph likely never occurred, it still conveyed a clear message, whether it was his own creation or given from the senate. Regarding Constantine’s triumph, Koortbojian works slowly through extant evidence to show that, despite clear reference with triumphi, Constantine likely never performed a triumph after defeating Maxentius in AD 312. Indeed, the arch’s imagery fails to align with other clear depictions of known triumphs in that Constantine would be celebrating a triumph for defeating Roman troops and that he is sitting in a carucca, not standing in a quadriga. Instead, the arch served as a means to support Roman institutional “fictions”—an idea which Koortbojian uses a few times in the volume—that effectively means it offered a vision of Rome that might not have been factually accurate, but supported a given ideology. In the case of Constantine, the arch accurately reflected his new status as ruler of Rome, but it did so by suggesting that he held a triumph, which almost certainly did not happen, if only for logistical reasons. Still, that does not mean that it did not reflect real ideas, primarily of Constantine’s power in the city.
There were some aspects of the volume that could have used improvement, but these were minimal. I noticed a few typographical errors, which did not hinder the work’s argument in any significant way. Another issue stems from the last phrase of the subtitle, “from Caesar to Constantine,” and is not unique to this book by any stretch. While the book ranges from Julius Caesar to Constantine, it is much more weighted toward the former than the latter, with greater attention given to Caesar and Octavian/Augustus than Constantine. In fact, Constantine is mostly reserved for the final chapter. Several intervening emperors—such as Tiberius, Hadrian, and Valentinian II—make appearances sporadically, but these are not studied as closely as those at either end of the range. Still, the work’s attention on the action of “crossing the pomerium,” is very focused, even if there might be other emperors or examples worth considering in future works.
Koortbojian’s study is a valuable resource for what it meant to “cross the pomerium” at Rome. It is especially valuable for its concision and for its useful and copious visual evidence. Likewise, its footnotes are an immense resource, offering succinct summaries of academic disagreement when needed but otherwise offering only necessary citations. The work sits beside other recent volumes that investigate space in Roman religious, political, and military spheres. It would be a worthy resource for scholars of these topics, but it might also be useful for advanced students studying one of these topics. Rather than attempting to define the precise borders or history of the pomerium from the foundation of Rome, Crossing the Pomerium instead focuses specifically on that titular action. Those other questions about its precise boundaries or its physical history still receive attention, but they do not serve as the fundamental framework for the volume. This helps the work to stand apart from other works on the pomerium, while also providing compelling evidence for those interested in Roman religion, politics, or military history.
 Attested by Pliny the Elder, HN 34.18.
 BC for AD referring to Vitellius’ crossing in 69 (p. 40, 42); “five differing scenarios” regarding magisterial status but only four enumerated (p. 63-64); “Cullhead 1994” for Cullhed 1994 (passim).
 For example, D. Gargola, The Shape of the Roman Order: The Republic and Its Spaces (University of North Carolina Press, 2017).