Mommsen _Conscriptionsordnung_ = Mommsen, _Die Conscriptionsordnung der römischen Kaiserzeit_, published in volume vi of the _Gesammelte Schriften_. von Dom. _Rangordnung_ = A. von Domaszewski, _Die Rangordnung des römischen Heeres_, Bonn, 1907. von Dom. _Sold_ = A. von Domaszewski, _Der Truppensold der Kaiserzeit_, in volume x of the _Neue Heidelberger Jahrbücher_. _J. R. S._ = _The Journal of Roman Studies._ INTRODUCTION THE MILITARY REFORMS OF AUGUSTUS 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. As a preliminary consideration it must be realized that the use of troops drawn from the subject races was not an invention of the imperial government, but goes back to the most flourishing days of the Republic. The heavy-armed yet mobile infantry which formed the greater part of the burgess militia of the _cives Romani_ and the _socii_ constituted an arm which won for Rome the hegemony of Italy, and triumphed alike over the numbers and courage of Ligurian and Gaul or the disciplined professional armies of Carthage and the Hellenistic monarchies. In other branches of the service, however, the republican armies were less superior. Their cavalry, drawn, as was usual in the citizen armies of the ancient world, from the wealthier classes, was not sufficiently numerous and proved no match for its opponents in the Second Punic War. The light troops came off even worse when engaged either with mountain tribes fighting on their own ground or with the skilled archers and slingers of Carthage or Macedon. So early was this recognized that, in describing an offer made by Hiero of Syracuse to furnish a thousand archers and slingers in 217 B.C., Livy is able to make the Syracusans justify the suggestion to Roman pride by asserting that it was already customary for the Republic to use _externi_ in this capacity.[1] To make up their notorious deficiency in this respect the Government could have recourse to three sources of supply. They could, as in this case, accept or demand contingents from allies outside the Italian military league, such as Hiero, Masinissa, or the Aetolians; they could make forced levies among subject tribes, such as the Ligurians, Gauls, or Spaniards; or, finally, they could imitate their