[138] In these cases an ethnical title may have been dropped, or omitted on the only inscriptions known to us.
[139] iii. 11930, 11931 (reign of Pius), 11933 (Commodus).
[141] For the position of the auxilia in the normal order of battle see below, p. 103. For Domitius Tullus and Domitius Lucanus, who held in turn the post of _praefectus auxiliorum omnium adversus Germanos_, probably in 73 and 74, see Dessau, _Inscr. Lat. Sel._ 990, 991, with notes.
[145] The diplomata of 133, 138, 148, 149, and 154 (D. xlvii, li, lx, lxi, and lxv) contain, on an average, ten regiments each. Four regiments are always present, and five more occur in four diplomata out of the five. This makes it sufficiently clear that, on the theory given above, the auxilia of the same legion must always be referred to, particularly in view of the immobility of the frontier troops in the second century (see below, pp. 114-16), which forbids the supposition that the same regiments would appear first attached to one legion, then, after a few years’ interval, to another.
[146] The earliest I know of is _legio III Augusta et auxilia eius_, which dates from 158. viii. 2637. Other instances are a dedication at Bonn by _legio I Minervia pia fidelis Severiana Alexandriana cum auxilis_ (xiii. 8017), and a Pannonian inscription of the reign of Gallienus which mentions _vexillationes legionum Germaniciarum et Brittanniciarum_ (at least this seems to be intended) _cum auxilis earum_. iii. 3228. The formula is certainly a rare one.
[147] _Studies in Roman History_, Second Series, p. 112.
[148] What exactly this amounted to is difficult to make out. It would be natural to suppose a system of military districts within the province. In Britain, for instance, the line between Tyne and Solway, with the auxilia upon it, might have been divided between Legio VI Victrix from York and Legio XX Valeria Victrix from Chester. Unfortunately the epigraphical evidence does not support the idea that the activity of the two legions was localized in this way. The point is obscure and would not have been worth such a detailed discussion but for the unwarrantable facility with which it is usually disposed of.
[149] Tac. _Ann._ iv. 5 ‘At apud idonea provinciarum sociae triremes alaeque et auxilia cohortium, neque multo secus in iis virium: sed persequi incertum fuit, cum ex usu temporis huc illuc mearent, gliscerent numero et aliquando minuerentur’. The _sociae triremes_, i.e. the Rhine fleet, &c., counterbalance the Italian fleets at Ravenna and Misenum.