Consecrated as the new capital of the Roman world in the year 330 ce, Constantinople was the ancient city of Byzantion, in origin a colony of Megara in Attica, and renamed the ‘city of Constantine’ by the first Christian emperor of the Roman world. He made it his capital in an effort to establish a new strategic focus for the vast Roman state, as well as to distance himself from the politics of the previous centuries. By the middle of the fifth century, the western parts of the Roman Empire were already in the process of transformation which was to produce the barbarian successor kingdoms, such as those of the Franks, Visigoths and Ostrogoths, and the Burgundians, while the eastern parts remained largely unaffected by these changes. When exactly ‘Byzantine’ begins and ‘late Roman’ ends is a moot point. Some prefer to use Byzantine for the eastern part of the Roman Empire from the time of Constantine I – that is to say, from the 320s and 330s; others apply it to the Eastern Empire from the later fifth or sixth century, especially from the reign of Justinian (527–65). In either case, the term ‘Byzantine’ legitimately covers the period from the late Roman era on, and is used to describe the history of the politics, society, and culture of the medieval East Roman Empire until its demise at the hands of the Ottomans in the fifteenth century.

This chapter focuses on the relationship between the state, attitudes to warfare as enshrined in Christian theory, and the practice of warfare as exemplified in medieval eastern Roman, or Byzantine, relations with its various enemies, with a short introductory section on violence in non-warfare contexts. While nominally opposed to violent means to achieve its ends, the Christian Byzantine state found ways to justify engaging in warfare against its enemies, primarily based on the notion that it was involved in a perpetual defensive struggle with those who threatened its territorial integrity as well as its moral existence. All warfare could thus be understood by definition as a defensive struggle against those who threatened the empire’s existence. This applied likewise to overtly offensive warfare, which was legitimated within a Christian eschatology as a divinely-approved effort to recover lost territories and restore them to the Christian community. Hence, no theory of ‘holy war’ or ‘crusade’ evolved, because such was irrelevant. Such an ideology offered a constant theoretical basis for fighting the empire’s foes; and it also served the needs of the imperial elite and the court on an opportunistic basis, to justify offensive warfare whenever the empire was in a position to undertake such action. Such an ideology legitimating warfare could also deployed against Christian neighbours, when it suited the interests of the imperial state or its elite.