Between AD 69 and 161 the composition of the Roman legions was transformed. Italians were almost entirely replaced by provincial recruits, men for whom Latin was at best a second language, and yet the 'Roman-ness' of these Germans, Pannonians, Spaniards, Africans and Syrians, fostered in isolated fortresses on the frontiers, was incredibly strong. Like the Italian yeomen who had battled Pyrrhus and Hannibal centuries before, the provincial legionaries were imbued with the traditional ethos of the Roman army. They were highly competitive, jealous of their honour, and driven by the need to...