This important monograph by Hansjoachim Andres investigates the structures and methods of diplomacy underpinning the relationship between the eastern Roman and Sāsānid Empires, focusing on the period between the partition of Armenia in 387 CE and the agreement regarding the fifty-year peace in 561/562. As Andres points out in Chapter 6, this choice rests on the acknowledgment that the two empires interacted according to a set of specific principles during this period. These principles or “rules of the game” that defined Romano-Sāsānid diplomacy are called “structures” by Andres and are covered in the first section of the book. The volume’s second part addresses what Andres calls the “methods” of late antique diplomacy. These concern how diplomacy was carried out on the ground and encompassed a wide range of practices: from treaties and oaths of mutual protection of high-ranking individuals to the involvement of humbler actors such as merchants, and from the gathering of intelligence to attempts at corruption and assassination. It is Andres’ contention that such tools were adopted only because their implementation made sense against the background of what the two empires thought possible to achieve. In other words, the structures of Romano-Sāsānid interactions dictated the methods through which they unfolded.
Andres understands diplomacy as the reciprocal influencing of two parties to create (or maintain) a common ground for continued interaction. As he argues, this contrasts with mainstream definitions in current political theory, where diplomacy is often equated with foreign policy (see Chapters 2 and 3). Such a distinction entails consequences for the analysis carried out in the book, starting with the chosen timeframe. As suggested by an exploration of Prokopios’ “archaeology” of the Persian Wars (pp. 145-157), different assumptions about, for example, the actual strength of the enemy and a changed geopolitical context – e.g., the coming of the Hephthalites or the Caliphate’s rise – significantly shifted the dynamics of the interaction between the two empires. Put differently, the strategies of these two empires shifted from a shared goal of influencing the other within a common field of interactions to all-out war aimed at the opponent’s destruction. Therefore, diplomacy between the two empires depended on specific conditions, which are not to be found either before or after the ca. 200 years on which the book focuses. Therefore, this period was chosen as a privileged window into the two empires’ strategy for shaping the world to their advantage without, however, being able – or willing – to change it by the use of force alone.
The volume is arranged in four parts for a total of 20 chapters. The introduction (Ch. 1) is followed by an important chapter on terminology. Here the author distinguishes diplomacy from foreign policy. Ch. 3 addresses the state of the art on the book’s topic in contemporary research. Ch. 4 details the structure of the argument in the main sections of the book. Ch. 5 presents the sources. Finally, Ch. 6 justifies the chosen timeframe.
The first section of the book (Ch. 7-10) then investigates the sociopolitical and intellectual premises – or “structures” in Andres’ terminology – of diplomacy, namely, the two empire’s efficacious but questionably accurate assumption of military balance, their equal standing as the only legitimate world powers, and the decision not to interfere with each other’s religious constituencies.
The second section (Ch. 11-19) investigates the methods for conducting diplomacy, including negotiations, agreements, and the role of law and war in creating advantageous conditions for pursuing economic or geopolitical goals. Significantly, Andres departs from viewing war as a way to liquidate the adversary, a prospect deemed impossible on account of the assumption of military balance (Ch. 13). Subsequent chapters widen the scope of this analysis to other methods, including guardianship and other forms of elite entanglement between the two courts (e.g., reciprocal gift giving: Ch. 14), the gathering of information concerning the enemy’s resources, manipulative strategies such as corruption, and, in extreme cases, homicide (Ch. 15-16). Finally, the focus of this section shifts away from the imperial courts and their networks of official ambassadors to the role of non-state actors such as doctors, bishops, and merchants, the display of symbolic gestures, and the attitude of the two empires towards minor peripheral powers (Ch. 17-19). A coda (Ch. 20) sums up the main findings of the book, followed by three appendixes on John Malalas’ diplomatic sources; the question of the so-called Achaemenid legacy in Sāsānid diplomacy; and the Mazdakite movement. A rich bibliography and detailed index of personal and collective names, places, and concepts rounds off the book, providing the reader with a compass with which to navigate its many threads.
Bruderzwist does not offer a play-by-play history of diplomatic events shaping the late antique east. Instead, it investigates the principles of geopolitical, legal, and even cosmological order which made the relationship and co-existence of these two empires possible in the first place. Crucially, as pointed out in Chapter 2, Andres emphasizes the mutual constitution of a diplomatic environment, which he understands as “the mutual modification of existing relations between two or more communities” (pp. 24-25). As pointed out above, scholars often subsume such an understanding of diplomacy under the concept of foreign policy. The latter, however, is understood by Andres as “the ability of a community – thus a political body – to exert influence beyond its territory.” Such a subsumption of diplomacy under foreign policy, according to him, focuses too much on what a given actor is able or not able to do. Accordingly, failure to exert influence is taken as a diplomatic seatback. This emphasis on power, however, clouds why Rome and Sāsānid Persia interacted with each other (and with other powers), the conditioning role of the templates (structures) investigated in the first part of the book, and why certain superficially counterintuitive strategies (methods) were chosen and other apparently reasonable ones were not. Given the consequences for the overall understanding of the period under investigation, the terminological and conceptual clarification at the heart of Andres’ analysis stands out as one of the major contributions of the volume.
Therefore, what is at stake is not ‘what actually happened’, as Leopold Ranke put it, but what ancient authors and political actors thought was happening and their explanations for why it was happening that way. The upshot of this methodology is that, once read against such a background, the evidence allows us, first, to identify recurrent patterns of diplomatic interactions. Secondly, once such patterns are assessed simultaneously against each other, they make it possible to sketch a political and cultural cartography of Rome and Persia’s engagement with one another with a new depth of analysis.
Chapters 8-10 are devoted to an exhaustive survey of the secondary literature to identify recurring issues and topics in modern research that might reveal the mental frameworks that underpinned ancient authors’ understanding of Romano-Sāsānian diplomatic interactions. At first, such a move appears counterintuitive. Why not focus instead on the ancient sources? However, as pointed out by Andres, it is difficult to proceed otherwise. For what participants in a given historical event take as self evident is not subject to explanation in their work, and it is therefore ipso facto left out of the narratives available to us.This is why it is often impossible to find explicit mention (much less a normative definition) of the cultural background of diplomacy in the evidence. However, it can be recovered by “upstreaming,” or reading the available sources against the grain of both the extant accounts themselves and the scholarly debate which they have generated. Certain puzzling issues, such as, for example, the stipulation of a peace agreement in a context in which continuing the war might have seemed more advantageous, allows us to guess the cultural categories that regulated the relationship between the empires and thereby better grasp the inner functioning of late antique diplomacy.
From Andres’s discussion, it emerges that wars of conquest were purposefully avoided even in the aftermath of an apparently decisive military victory. Such behavior is explained by the underlying assumption of equal military strength, a characteristic structure of this period, according to Andres, and one conditioned by imperfect knowledge and intelligence gathering (Chapter 15). It is important to stress that the actual equivalence of the two armies did not really matter. It was enough that both empires understood their armies to be roughly equal for them to act accordingly. From this first premise follows, in Andres’s view, a second, no less momentous one: the mutual understanding of each empire as an equally legitimate world power who could not be challenged in the same ways that minor polities or mobile confederacies such as the Goths or the Huns could. The third structure identified by Andres, specifically the imperative not to interfere in religious matters internal to the political dynamics of the other empire, is a further consequence of the second. A peculiar aspect of the book’s timeframe is that these three structures were present simultaneously only during these two centuries. This suggests, according to Andres, that it was only under these conditions that diplomacy could have been both thinkable and successful. In the absence of even one of these three structures, this equilibrium was either impossible to establish in the first place (as illustrated by the first phase of Sāsānid expansion in the west) or difficult, if not impossible, to reconstitute once torn apart. The increasing sacralization during the seventh century CE of the emperor’s figure in Constantinople and in Persia critically undermined both the principles of equal legitimacy and religious neutrality. Therefore, a series of devastating military confrontations ensued. The result was one empire’s extinction and the other’s near collapse, which supports Andres’s argument about the role of the structure in making diplomacy both possible and successful.
Chapter 11 links the two main sections of the volume by laying out the methodology that is to be utilized in the following chapters. Once more, definitions are paramount. According to Andres, methods are ‘the categories of diplomatic action’ (cf. pp. 134-139). They showcase how the empires sought to influence each other within the cultural frameworks set by the structures and according to the rules of the diplomatic game they established. From this point onwards, a thorough investigation of the available evidence comes to the fore to exemplify how the above-defined structures worked on the ground.
Chapters 12-19 are each devoted to the detailed study of one method. This aim is achieved by carefully selecting key episodes and anecdotes (such as Priskos’ embassy to Attila) from an impressively wide range of sources. Such a broad corpus allows Andres to illustrate in practice how the structures investigated in the first part of the book regulated the daily workflow of political interactions across space, time, and, on occasion, cultural barriers. To name one example, it is only against the backdrop of the first two structures (the assumption of equal military strength and the mutual understanding of each other as the only legitimate world powers) that peace treaties were negotiated and certain metaphors, such as that of brotherhood, were deployed (as explored in Chapter 12). The case of military encounters is also instructive. As demonstrated in Chapter 13, it is only thanks to the simultaneous operation of the three structures that war never escalated beyond a certain threshold – in contrast to what regularly happened before and after the timeframe discussed in the volume. In fact, according to the sociocultural premises that are discussed in the book’s first part, it becomes clear that warfare acted as one avenue among many to modify the existing power balance to the advantage of one side without any pretense to the liquidation and conquest of the adversary. What was at stake, in other words, was the preservation of a common ground for dialogue and not just the pursuit of strategic gains, as a foreign policy approach implies.
The equal rank of the two powers as a crucial structure for carrying out diplomacy is best exemplified in Chapter 14. Here, Anders investigates both the much-discussed episode of the guardianship of Theodosios II by Yazdgard I (often, as argued in Chapter 14, incorrectly called his “adoption”) and that of Justin I over Ḫusrow I. According to Anders, this strategy created a common ground for diplomacy in that it made one emperor responsible for the wellbeing of the other’s son. However, such a step was made possible only by the mutual recognition of the two empires as the only legitimate powers on stage, what Anders calls the diplomatic structure of equal rank. The gathering of information and intelligence, moreover, appears in a new light once the assumption of equal military power is factored in (Chapter 15). At the same time, the inordinate amount of effort that both courts put into impressing each other’s envoys, as well as preventing them from acquiring intelligence, becomes easier to understand. It might, in fact, be taken as a move to uphold the impression of equal military power, without which diplomacy became suddenly endangered, as one of the empires might have wanted to capitalize on its strengths. As for the dark side of diplomacy, it is interesting to point out that it was used mostly, if not exclusively, for reasons of internal politics and never against the other power (Chapter 16).
The second of the above structures implies that it was not deemed possible for either side to turn to a third party for the resolution of thorny disputes. This was because there was no one else endowed with the same authority and legitimacy as the two world powers. Thus, it becomes easier to understand the occasional recourse to individuals outside the network of court diplomacy, such as bishops, doctors, and even merchants, insofar as they did not act as officially sponsored ambassadors. This is a typical example of what Andres calls “track-two diplomacy,” or the pursuit of one diplomatic target by making use of multiple negotiatory channels, as covered in Chapter 17. Such a strategy chiefly aimed at avoiding conflicts while never forfeiting the goal of “mutual modification of existing relations” (p. 24). This emerges most conspicuously from an investigation of symbolic gestures such as embassies and ritual performances staged at court or in public settings such as the hippodrome (Chapter 18). Moreover, it is worth emphasizing that the influence of the structures identified by Andres can be seen at work far beyond the courts of Constantinople and Ktesiphon. In particular, Andres demonstrates this in the case of the southern Caucasus, the Arabian peninsula, and eastern Africa (Chapter 19). The importance of such a detailed focus on regions which initially appear as political backwaters becomes apparent if one considers that scholarship is still keen to treat local stakeholders either as passive recipients of the power strategies of the major actors or as taking part in a zero-sum game wherein one only gains as others lose. As the methodology adopted here shows, the main flaw of such an approach is that it ignores the structurally multidirectional nature of diplomacy (pp. 24-25), thus depriving seemingly peripheral actors of their own agency.
In sum, Bruderzwist is a highly innovative contribution both to the scholarship on late antiquity and on diplomacy, ancient and modern. It provides valuable stimuli for cross-imperial comparative history, and its potential for a more sophisticated rethinking of Eurasian interactions should be duly considered in future research.
 Cf. already Matthew Canepa, The Two Eyes of the Earth: Art and Ritual of Kingship between Rome and Sasanian Iran (Berkeley: University of California Press, 2009), focusing on what Andres understands as only one method of diplomatic interaction between the two empires.
 See Pekka Hämäläinen, The Comanche Empire (New Haven: Yale University Press, 2008), pp. 1-17, and Camilla Townsend, Fifth Sun: A New History of the Aztecs (Oxford: Oxford University Press, 2019), pp. 1-12 for a discussion of precisely such a methodology (upstreaming) in contexts plagued by scanty written sources which moreover often provide a patchy and biased coverage of the events they deal with.
 See Julian Wünsch, Großmacht gegen lokale Machthaber. Die Herrschaftspraxis der Seleukiden an den Rändern ihres Reiches (Wiesbaden: Harrassowitz, 2022) for a recent example of precisely this kind of approach, moreover in the context of a space, that of Seleukid Iran, which considerably overlaps with the one covered in the monograph under consideration.
 Compare Robert Rollinger, ‘Contextualizing the Achaemenid-Persian Empire. What does Empire mean in the First Millennium BCE?’ In “Achaemenid Studies Today”. Proceedings of the SIE mid-term conference held in Naples, edited by G. Basello, P. Callieri, and A. V. Rossi. Naples: “L’Orientale” University Press, 201-248 for an insightful discussion of borderland politics in the context of the Achaemenid empire as engaging proactively with (and not just reacting to) the diplomatic framework outlined by the Great King and his satraps.
 Xi Wen, The King’s Road: Diplomacy and the Remaking of the Silk Road (Princeton: Princeton University Press, 2023) may be taken as a first attempt in this direction.