This chapter will discuss the types of war fought by the Roman army in the late Republic and Principate. It will consider the context in which these conflicts occurred, their frequency, duration, decisiveness and results. Yet, although our main theme is Roman warfare, we should never forget Isaac’s point that any conflict involves at least two sides. The Romans did not wage war in a vacuum, but against opponents who had their own reasons for fighting and their own expectations of how the conflict would be fought and what its outcome should be. (In the main, Roman armies fought against foreign peoples, and civil wars will be treated separately.) The military culture and practices of Rome’s opponents were as important in shaping each conflict as the behaviour of the Roman army. It is vital to study these, even though the overwhelming majority of our evidence must come from Greek and Roman accounts and such sources may contain deliberate distortions, cultural misunderstandings and straightforward errors.