Diplomatic contacts and an intensive exchange of information regarding a variety of issues – economy and trade, the security of the borders, religious and cultural matters etc. – formed an important part of Roman– Persian relations. However, it was above all the military confrontations that characterised Rome's relations with her Eastern neighbours. These were as numerous as they were of long duration. Both powers' claim to universal rule pointed out in the previous chapter did not leave any room for a stable coexistence on the basis of international law. Almost inevitably, or rather instinctively, any perceived or real weakness provoked the military initiative of the opponent so that from the third into the seventh century a state of war between the two has to be seen as ‘endemic’. The analysis of these military confrontations is therefore predominant in this study, not because of an imbalanced modern view of Roman–Sasanian relations that adopts a ‘confrontational perspective’ but because of the actual historical events, which were experienced and analysed by the contemporary observers in a similar way. These also emphasise the opposition between West and East and focus on sometimes very elaborate descriptions of a permanent struggle for a powerful position and strategic advantages in the Near and Middle East. This is – and rightly so – reflected in modern scholarship, which has always paid particular attention to questions of peace and war as well as triumph and defeat. Our diachronic survey thus includes a detailed account of the rivalry between the two powers as it is expressed in the numerous military confrontations. The theatres of war included both the Eastern Roman provinces and the Western regions of the Sasanian Empire.