Strategic intelligence - that is, information about the activities and affairs of potential enemies relevant to a state's strategic concerns - is an important factor in the foreign relations of any state. This thesis investigates the role of strategic intelligence throughout Roman relations with Sasanian Persia (early 3rd to early 7th century A.D.) and in the empire's relations with northern peoples beyond the Danube, Rhine, and Hadrian's Wall while these remained imperial frontiers during the same period. Two broad questions are addressed. The first concerns the extent to which strategic intelligence moved between the empire and these neighbouring peoples, and its consequent role in their relations. The second concerns the means by which this information moved. Chapters 1 and 4 consider the first question for relations with Persia and with northern peoples respectively. The first chapter argues that strategic intelligence moved between the Roman and Persian empires with a high degree of regularity: neither could mount a major invasion without the other having some foreknowledge, and both frequently undertook aggressive action so as to exploit knowledge of the other's disadvantages. It is therefore argued that strategic intelligence had an important role in determining the pattern of aggression in Roman-Persian relations, but also in limiting the overall level of warfare between them across four centuries. Chapter 4 concludes that while strategic intelligence also traversed the northern frontier, it did so with less regularity than in the east, with the result that relations in the north were less stable. Chapters 2 and 3 consider how strategic intelligence moved between the Roman and Persian empires. Attention is given to the use of embassies and spies in the gathering of intelligence about military preparations and other indicators, but it is argued that such information also made its way informally between the empires as part of the intensive cross-frontier interchange which characterised northern Mesopotamia. Chapter 5 argues that such interchange was less frequent across the northern frontier, and that the more limited degree of state formation among northern peoples (compared with Persia) meant that information gathering through spies and embassies was also less effective. The Conclusion draws together the results of this comparison of east and north, and reflects on the implications of the argument for the debate about continuity of the empire in the east and its demise in the west.