Rome and the Enemy: Imperial Strategy in the Principate

Many modern historians, most notably Luttwak, have tried to explain the strategy of the Roman Empire in terms that make sense to modern strategic thinkers, citing concepts like natural frontiers and cost-benefit analyses. Mattern argues we should instead take ancient historians seriously when they tell us that Roman foreign policy was primarily based on considerations of honour, prestige, and glory, with some allowances made for military and financial practicalities.

I found it convincing - though note I haven't read the authors arguing for a more rationalistic Roman strategy.