• diplomacy
• epistolography
• interstate dialogue
• late antiquity
• roman history
• sasanian history

For several decades now, the study of Roman-Sassanid relations has been a fertile research field within the sphere of Late Antiquity and in the that of interstate relations. This thesis intends to insert in this line of studies, taking into consideration an aspect that is still little considered in Late Antiquity diplomacy such as diplomatic correspondence. This work constitutes a systematic examination of the entire diplomatic correspondence between Roman and Sassanid sovereigns throughout the period in which the two major late antique powers maintained reciprocal relations, from the 3rd to the first half of the 7th century CE.
The study considers 14 examples of epistolary texts, attributed both to Roman emperors and Sassanid rulers, contained in Greek, Latin and Armenian historiographic sources. In particular, we would like to analyse: a) how the two empires self-represented and interacted between each other from the correspondence; b) how diplomatic language was formed between the two empires and what were the preferential channels of communication; c) verify the above issues starting from the surviving documentation. This is not an easy task due to the heterogeneous nature of the sources and the variety of languages with which information on this type of correspondence has been transmitted.
From a methodological point of view, the careful examination of the evidence we have received presupposes, at first, the verification of the authenticity of the documents reported in the historiography. A limitation of the research is the unilateral nature of the documentation, coming exclusively from the Eastern Roman Empire. What is more, there are also questions related to the nature of the sources examined: even if historiographers claim to having faithfully reported the epistolary texts, various elements contrast this statement: the authors may have modified the letters on the basis of the rules of the genre historiographical, in particular by rhetorically modifying the original text or adapting them to their literary models. Consequently, this work uses, on the one hand, a philological-literary approach and, on the other, a historical-comparative method: for this last point, an important role is played by the comparison with texts and sources from the Sassanid empire, which can confirm or deny the information in the epistolary texts attributed to the Persian kings. Once the authenticity, or rather, the reliability of the documents has been established, the significance of the letters for the relations between the two empires is investigated.
The research opens with an introductory reconstruction of the historical context of Roman-Sassanid relations, to better outline the evolution of the complex relations between the two empires between the 3rd and 7th centuries CE. Despite its concise nature, this section appears necessary for understanding the documentation at issue. From the beginning, the relations between the two empires appeared as the complex attempt to find an understanding between two state entities that aspired to universal hegemony, supported by a providential religious vision and, therefore, legitimising this "mission" in history. This is the religious-cultural framework that characterised the relations between the two empires during the 3rd century: the confrontation often resulted in fierce war conflict, with frequent defeats by the Romans. The first chapter, dedicated to the analysis of the correspondence between Severus Alexander and the Persian king Ardaxšīr reported in Herodian, belongs to this climate of strong rivalry. From the analysis of this text, it can be seen how the two sovereigns were united by the use of historical memory in the construction of a diplomatic discourse: therefore, Ardaxšīr used history as a way to justify his expansionist aspirations. At the same time, in Severus Alexander’s letter, historical memory was used to strengthen the prestige of the Romans in the East and to constitute an effective response to the Sassanid menace.
The second phase of the Roman-Sassanid relations, which extends from 297/8 to 387, was characterised by a search for a balance of forces. Important for further development of Romano-Sasanian relations was the treaty of Nisibis of 298/9 concluded between Diocletian and King Narseh, which constituted a real turning point in the relations between the two empires. Despite the Roman military victory, Diocletian preferred to use moderation, recognising to the Persians an equal role compared to the Roman Empire. The subsequent treaties concluded in 363 and 387, beyond the peculiar aspects of the moment, fit within this line, with the attempt to find an appropriate compromise to ensure border security. This situation of balance of power characterized the political and religious background of two documents analysed in the second and third chapters: chapter 2 analyses the letter of Constantine to King Šābuhr II, reported by Bishop Eusebius of Caesarea, in which the emperor uses Christian themes to guarantee the balance achieved after the Treaty of Nisibis. Chapter 3 examines the correspondence between Šābuhr II and Emperor Constantius II contained in the historical work of Ammianus Marcellinus. Also, in these letters we can see how the two sovereigns, despite their differences on how to understand the balance of forces between the two empires, recognised that they were on an equal level and constituted the main political actors in the international scenario.
The 5th century was characterized by intense diplomatic contacts to favour processes of collaboration for the defence of the common border threatened by the nomadic peoples from the Northern Caucasus. Consequently, this period was a long period of peace between the two empires, apart from two short wars in 420-1 and 440/1 CE. The two empires mutually recognised each other, projecting this situation also on the level of the personal relationships of kings and reigning families. And it was precisely the dynamics of personal relationships between sovereigns that are one of the privileged strategies of diplomatic contact. In this regard are relevant the documents examined in chapter 4, referring to proposals for family alliances and kinship, through the practice of adoption and reported in the Bellum Persicum of Procopius of Caesarea (Arcadius / Yazdegerd I; Kawād / Justin I).
In the 6th century, we can see the return of the climate of tension which alternates with periods of peace - which hopefully will also be "eternal" or long-lasting - and long periods of heated conflicts. Despite these difficult relations, the two kingdoms developed diplomatic strategies that were to lead to the construction of a stable peace, continuing to recognize each other and to cooperate. This situation fits well in three letters relating to the reign of Justinian, which are analysed in chapter 5.
The last phase of the Roman-Sassanid relations (590-630) was characterized by the long reign of king Xusraw II. It can be divided into three main periods: from a period of strong collaboration between the two empires, with the agreement between Xusraw and the emperor Maurice, it passed to the open war triggered by the usurpation of Phocas in 602 and continued under the reign of Heraclius, during which the Persians tried to definitively subdue the Romans. With the death of Xusraw II in 628, Romans and Persians recovered that climate of cordiality and cooperation prior to the outbreak of war in 602. Indicative of this phase are chapter 6, which examines Xusraw II’s letter to Mauritius, and chapter 7, which examines the diplomatic correspondence between the two empires during the reign of Heraclius.
The last chapter takes up the overall question of the forms of diplomatic communication between the Roman and Sassanid empires, as indicated in the letters. The chapter focuses on the analysis of three issues - such as the existence of an international order, justice and expressions of balance of power - which constitute the main themes common to all the letters. The analysis clearly shows that these issues had an autonomous origin within the cultural horizons of the two powers, but the unceasing exchanges of embassies over time have led to their adoption to develop forms of interstate dialogue. Finally, a brief appendix follows, that offers an overview of the ancient Greek, Latin, Syriac and Armenian literary sources that transmitted this type of correspondence.
In conclusion, we can note how the diplomatic letters transmitted in our sources offer important information on the functioning of the Roman-Sassanid diplomacy: despite the different types of modifications these texts are subjected, the letters are not the result of invention, but have a historical core irrefutable. Furthermore, it clearly emerges that this correspondence is part of an intercultural dialogue that has led to the formation of a real diplomatic language that is mutually understandable by the two powers.