This detailed examination of the way in which the Roman army operated during a war and how it fought a battle breaks away from existing studies, which mostly concentrate on the army in peacetime, and attempts to understand the army as an institution whose ultimate purpose was to wage war. Adrian Goldsworthy explores the influence of the Roman army's organization on its behaviour during a campaign, emphasizing its great flexibility in comparison to most of its opponents.

He considers the factors determining the result of a conflict and proposes, contrary to orthodox opinion, that the Roman army was able to adapt successfully to any type of warfare. Following the technique pioneered by John Keegan in The Face of Battle (1976), Dr Goldsworthy builds up a precise picture of what happened during battle: tactics employed, weaponry, leadership, behaviour of individuals as well as groups of soldiers, and, of utmost importance, morale.