Throughout the first century AD, the emperors of Rome faced various threats to their rule from ambitious or embittered nobles. However, events show the Roman legionaries to be tenaciously loyal to the Julio-Claudian dynasty. The murder of Nero, the last of his dynasty, unleashed chaos where allegiance was bought by ‘the madness of the leading men.’ The troops, increasingly recruited from men who had never seen Italy, were often happy to draw their swords in support of a provincial governor against an emperor who was himself a victorious usurper. If successful in raising their own...