An essay on the Roman auxilia might seem merely to be one of the many monographs in which students of the military system of the Roman Empire are patiently arranging material for some future scholar to utilize in a more comprehensive work. But while much space must necessarily be devoted to details of military organization, the subject opens up social and political questions of wider range. The extent to which a ruling race can safely use the military resources of its subjects and the effect on both parties of such a relation, the advantages and dangers of a defensive or an aggressive frontier policy, these are questions of universal historical interest, on which even an essay of so limited a scope as this must necessarily touch in passing...