A graphic pitched battle narrative or detailed description of a siege (complete with gruesome embellishments) was a must for any decent history. The tactical flexibility offered by the auxiliary units was especially valuable in the smaller-scale wars of the imperial period, and for frontier and internal security. This applied most of all to the part-mounted equitatae units. Naval battles were more likely to be influenced by the vagaries of weather and wind than land battles, so there could be some delay before conditions allowed a battle to take place. Rome had traditionally been a successful besieger and was able to maintain an army over the winter if necessary. Roman military thinking believed that a pitched battle fought on a fair or level battlefield would bring a certain victory. The tactical manuals provide some insight into how the Romans themselves explained their military success.

This chapter assesses the factors which distinguished Roman armies from their various opponents: the tactical roles of the different troops deployed; their training, discipline and morale; and whether their attitudes to and preparation for combat were equal to the operational tasks they faced. Like their predecessors, later Roman emperors and officers embarking on military operations had at their disposal a number of military treatises or tactica. While Roman cavalry became more effective in fulfilling its existing tactical roles, the fundamentals of mounted combat remained unchanged. Sieges constitute over half the military engagements in late antiquity. Given the relative rarity of large-scale Roman offensives before the sixth century, Roman troops were ordinarily in the role of defenders, and more likely to be limitanei than comitatenses. This changed perspective is evident in contemporary treatises, which hitherto dealt almost exclusively with offensive siegecraft.