Since this military system, with its division of the troops into categories differing from each other in status and prestige, reflected the general conditions prevalent in the Empire, so it was inevitable that a change in these conditions should have its effect also upon the army. How far the political developments of the first century were foreseen or intended by Augustus it is perhaps impossible to say; it is certain, at any rate, that his system was capable of adapting itself to them. One of these developments was a steady increase in the power of the central government and a disappearance of all forms of local autonomy which involved a division of authority. By the reign of Vespasian almost all the great client kingdoms had been more or less peaceably absorbed into the ordinary provincial system. Cappadocia was annexed in 17, Mauretania in 39, Thrace in 46, Pontus in 63, and Commagene in 73. The troops which these kingdoms had maintained were naturally taken into the Roman service, transformed into auxiliary regiments, and lost the privilege which attached to their former condition of serving only in local campaigns. One instance of such a transference, in the case of a regiment which had been in the service of the kings of Pontus, is mentioned in Tacitus,[23] and we also meet with Hemeseni on the Danube,[24] Commageni in Africa and Noricum,[25] and the successors of one of Herod’s old Samaritan regiments in Mauretania.[26] The resentment with which the new conditions of service were sometimes received is an instructive comment on the wisdom of Augustus’s policy in not enforcing their universal applicability at an earlier date. The Thracians, for example, rose in open revolt when they were first summoned to supply a contingent for service at a distance from their own borders.[27] Somewhat similar was the fate of the border militia on the Rhine and Danube. On the latter frontier the revolt of 6-9 showed at an early date the dangers of the system. After its suppression the clan chiefs seem, in many cases at any rate, to have been deposed and replaced by Roman officials,[28] regiments of Pannonians and Dalmatians were raised and transferred to other provinces, and a garrison was imported from outside to control the country.[29] On the Rhine the process was a more gradual one. The Batavi, for example, whom we have noticed serving in the campaigns of Germanicus as a clan levy under their dux Chariovalda, seem to have been organized in regular auxiliary regiments by the middle of the first century,[30] although they still retained, in common with many other corps of Rhenish auxilia, their clan chiefs as their praefecti.[31] In the year 69 we also find the Helvetii still responsible for maintaining the garrison of a fort within their borders, and a militia existing in Raetia capable of supplementing the garrison of regular auxilia.[32] Some even of the Gallic states, which were more distant from the frontier, sent contingents to support Vitellius, which were not, however, regarded as a very sensible addition to his forces.[33]
Probably these last vestiges of independent organization and control were swept away at the time of the reorganization of the Rhine army in 70, after the rebellion of Civilis. From this date onward there are at any rate few traces here or elsewhere of any use of irregulars of this type by the military authorities. This militia, which might have proved invaluable in the days to come as a national reserve, fell a victim, together with the local autonomy on which it was based, to the growing tendency towards centralization which marks the first and second centuries. The supersession of local officials by the agents of a centralized bureaucracy in the civil administration coincides with the complete transference of the burden of the defence of the state to the shoulders of a professional army. It is the purpose of the following chapters to discuss one part of this army, the auxilia, to trace its organization and the part which it played in frontier defence, and to illustrate from this study the lines on which the military system of the Empire developed and the causes of its failure.
FOOTNOTES:
[1] Livy, xxii. 37 ‘Milite atque equite scire nisi Romano Latinique nominis non uti populum Romanum: levium armorum auxilia etiam externa vidisse in castris Romanis’. Cf. Polybius, iii. 75.
[2] Cf. Varro, De Lat. ling. v. 90 ‘auxilium appellatum ab auctu, quum accesserant ei qui adiumento essent alienigenae’. Festus, Epit. 17 ‘auxiliares dicuntur in bello socii Romanorum exterarum nationum’.
[3] Livy, xlii. 35.
[4] Livy, xliii. 7.
[5] Plutarch, Vit. C. Gracchi 16; Caesar, Bell. Gall. ii. 7.
[6] The famous occasion when Caesar, distrusting his auxiliaries, mounted some of the tenth legion, proves conclusively that he had then no citizen cavalry in his army. Caesar, Bell. Gall. i. 42.