The evidence hitherto considered has mainly served to illustrate the original distribution of the burden of military service and the respective quotas furnished by the different provinces to the auxilia at the time of their organization. To trace the further workings of this system it is necessary to examine the principles on which the auxiliary regiments were distributed among the military areas and to trace the relations between this distribution and the method of recruiting.
A casual glance at the military diplomata, which give a fair idea of the composition of the more important provincial garrisons between the reign of Vespasian and that of Commodus, suggests that it was the settled policy of the imperial government to destroy the possibility of national cohesion and local sympathies among the regiments raised from their subjects by distributing the contingents of each recruiting district over as wide an area as possible, and making every frontier army corps a mosaic of different nationalities. It will be shown later that this theory, which has been frequently adopted by modern writers, will not stand before a closer scrutiny of the evidence as an explanation of the state of things existing in the second century; it can also be shown that such a principle of distribution was not the original policy inaugurated by Augustus.
Our earliest evidence relates to the composition of the garrison of the Danubian provinces, and the account of the great rising which took place here in the year A.D. 6 by the contemporary observer Velleius makes it clear that the strength of the rebels lay in the training which many had received in the Roman army. His reference to the military knowledge of the leaders and the discipline of the rank and file indicates that regular auxiliary regiments, raised locally and stationed near their homes, had mutinied in sympathy with their fellow tribesmen.[199] Concerning the state of things on the Rhine frontier we have more detailed information which points to the same conclusion. The account in the _Annals_ of the campaigns of Germanicus mentions cohorts of Raeti, Vindelici, and Gauls in addition to the _tumultuariae catervae_ of the local militia.[200] Later in the century we find an Ala Treverorum engaged in putting down a revolt of their own countrymen in 21,[201] an Ala Canninefatium engaged in the disastrous expedition of L. Apronius against the Frisii in 28,[202] and Vangiones and Nemetes helping to repulse a raid of the Chatti in 50.[203] Finally, when we turn to the narrative contained in the _Histories_ of the events of the disastrous year 69, we find abundant evidence that at this date three-fourths of the Rhenish auxilia were drawn from Gaul proper or the Teutonic tribes of Belgica. The only regiments mentioned by Tacitus which are not of local origin are (1) Thracians, who appear on every frontier owing to their special qualifications as archers;[204] (2) Spaniards, who may have entered the province in 43 with Legio IV Macedonica, which was transferred from Spain to the Rhine to replace the troops sent to Britain, and (3) Britons, who probably began to arrive from the newly conquered areas a few years later.[205] Epigraphical evidence adds to the list a few regiments from the Danubian provinces and some corps of oriental archers.[206]