The Auxilia of the Roman Imperial Army

by George Leonard Cheesman

The fact that two privates occupy the fourth and fifth places shows clearly that the holders of all the posts mentioned lower in the list belong to the immunes. Had it not been for this piece of evidence we might have been tempted to place the signifer turmae in the higher category. The analogy of the Equites Singulares also suggests that we may include the bucinator and tubicen among the immunes of the ala,[100] and we have also to add the medicus, whose somewhat exceptional position is discussed later.[101]

A distinction between the principales and immunes of the cohorts may be based partly upon the principles already adopted for the ala, partly upon the analogy of the legion, the organization of which was clearly followed in several respects. On these grounds we may class as principales the imaginifer cohortis, the signifer, optio, and tesserarius of each century, and the optio and vexillarius of each turma in the cohortes equitatae. The case of the optio, who commanded, if necessary, in the place of the centurion or decurion, may be taken for granted. It may also be noted that both optio and vexillarius could be promoted to the position of decurion without any intervening step.[102] The tesserarius, whose main duty consisted in receiving from the centurion the orders and password for the day and transmitting them to the men, is found in charge of a detachment on special duty,[103] as is also the imaginifer cohortis.[104] The signifer,[105] lastly, can hardly have had a position inferior to that of the vexillarius or tesserarius, and would indeed rank higher than the latter if the analogy of the legions holds good. As regards the immunes, the officer commanding a cohort possessed a smaller administrative staff than the praefectus alae, including only the cornicularius,[106] actarius,[107] librarius,[108] and beneficiarius.[109] The musicians possibly include the cornicen[110] as well as the tubicen[111] and the bucinator[112], and the post of mensor seems to be confined to the cohorts.[113] At least no inscription has yet mentioned one among the immunes of the ala.

Finally, as regards the position of the medici, who were attached to the cohorts as well as to the alae, a few special remarks seem necessary. On a British inscription one of these army doctors is described as medicus ordinarius[114], which would naturally mean that he served in the ranks, and a passage in the Digest confirms this by ranking the medici among the immunes.[115] On the other hand, M. Ulpius Sporus, who is described in an inscription erected by his freedmen at Ferentinum in Etruria as medicus alae Indianae et tertiae Astorum (sic)[116], seems to be on rather a higher level, as also M. Rubrius Zosimus of Ostia, who was doctor to the Cohors IV Aquitanorum in Germania Superior in the second century.[117] Both these men are apparently Greeks, and can hardly have reached their regiments by the ordinary recruiting channels.[118] It has been noticed also that the medici appear to have a special position in some inscriptions of the Praetorian cohorts.[119] Probably, then, one may infer two classes of medici, the common soldier who possessed some elementary qualifications (first aid and blood-letting) and was given the position of an immunis, and the fully-trained professional doctor who was attached to a regiment but held no actual military rank. It was probably to distinguish himself from the latter class that the medicus of the Tungrian cohort added the word ordinarius to his title.

As regards the rate and method of promotion, and the order of precedence of the various posts within the two groups of principales and immunes, we know practically nothing. There is nothing to show that it was customary to hold several posts in a regular order,[120] or to become an immunis before entering the principales. It was doubtless usual for a man not to receive commissioned rank without first holding some subordinate post, but we do not know that any such preliminary qualification was essential.[121] Owing to the length of service promotion was probably not rapid, but on the other hand the number of posts available was very large. In an ala quingenaria, for example, there were 16 decurions, 34 principales, and probably over 100 immunes.[122] Thus every soldier must have felt confident of obtaining sooner or later a position of greater ease and profit, and this, together with the fact that the ladder of promotion led to commissioned rank, and even to the coveted legionary centurionate, must have increased the attractions of the profession.

Titles of the regiments. The titles of the auxiliary regiments were as various in form as those of the legions, and it is unnecessary to give a complete list of them. The alae which bear a title derived from a personal name, presumably that of their original commander, have been mentioned already. The majority of them were probably raised during Caesar’s Gallic campaigns or the Civil Wars, and there are few to which a later date can be assigned with any certainty.[123] The few cohorts known to have borne such titles are more difficult to explain, but have perhaps a similar origin.[124] Regiments raised under the Empire, on the other hand, were usually called by the name of the tribe or district from which they were raised, and distinguished by a number from other corps of the same origin.[125] In course of time these ethnical titles were in many cases supplemented by others, some of which were granted as marks of distinction and rewards for meritorious service, while others were purely descriptive. Examples of the former class are the title civium Romanorum, which indicates that on some occasion all the members of a corps received the franchise before their discharge,[126] and honorary epithets, such as pia, fidelis, or fida.[127] The title Augusta seems also to have been granted at all periods honoris causa, although some of the regiments bearing it may date back to the beginning of the Empire.[128] Titles derived from the names of later emperors, on the other hand, while they were doubtless granted occasionally as marks of distinction, seem often to indicate nothing more than the reign during which a regiment was raised. Finally, from the time of Severus Antoninus onwards, every regiment employs a secondary title, derived from the name of the reigning emperor. A remarkable series of dedicatory inscriptions of the Cohors I Aelia Dacorum, which was stationed during the third century at Birdoswald (Amboglanna), on the British frontier, shows us this regiment successively assuming the titles Antoniniana, Gordiana, Postumiana, and Tetriciana.[129]

Purely descriptive titles might be derived either from the size of the regiment (miliaria, quingenaria), its composition (equitata, gemina),[130] its weapons (scutata, contariorum, sagittariorum), or the name of the province in which it was or had been stationed (Syriaca, Moesiaca). A frequent motive for the assumption and accumulation of such secondary descriptive titles seems to have been the desire of a regiment to distinguish itself from another unit bearing the same number and ethnical title, and stationed in the same province. This was probably the origin of the title veterana or veteranorum, which was borne by five alae and five cohorts,[131] although its interpretation is much disputed. According to von Domaszewski, these regiments were so called because they were originally formed of discharged veterans recalled to active service in time of war.[132] Cichorius suggests that a regiment assumed this name when another corps bearing the same number and ethnical title, but of more recent origin, was stationed in the same province.[133] This certainly furnishes the best explanation in the case of the Cohors III Thracum c. R., and the Cohors III Thracum veteranorum, which appear together in the Raetian diplomata for 107 and 166.[134] On von Domaszewski’s theory it is difficult to see why a regiment of recalled veterans should bear the number III, and his explanation that ‘the numbers borne by these corps are connected with the numbering of the auxilia in the province to which they were attached after their formation from missicii’ does not make matters much clearer. Cichorius’s suggestion would also account satisfactorily for the Cohors I Aquitanorum and the Cohors I Aquitanorum veterana, which appear together in Germania Superior in 74,[135] and the Cohors I Claudia Sugambrorum and the Cohors I Sugambrorum veterana which were stationed together in Moesia Inferior.[136] The latter would be identical with the regiment mentioned by Tacitus as forming part of the garrison of the province in the reign of Tiberius.[137] In other cases where similar duplication cannot be proved it must be remembered that our evidence is very imperfect, and that a regiment after assuming this title may have continued to use it when the reason for doing so had disappeared.

These descriptive and honorary epithets, although sometimes borne alone,[138] were usually employed to supplement the original ethnical title, with the result that after a hundred years of meritorious service the ‘full style’ of a second-century regiment might be almost as long and imposing as that of the emperors whom it served. As an example, one may cite the Cohors I Breucorum quingenaria Valeria Victrix bis torquata ob virtutem appellata equitata, which formed part of the garrison of Raetia.[139]

Relation of the auxilia to the legions. It is perhaps relevant to discuss here a point affecting the auxilia as a whole, namely, their relation to the legions in the general scheme of military organization. It is generally supposed that in those frontier armies which included both classes of troops, a group of auxiliary regiments was definitely attached to each legion, and such phrases as ‘a legion with its attendant auxiliaries’ are common in writers on the military system of the Roman Empire. Evidence as to the exact nature and even the existence of such a connexion is, however, somewhat difficult to find. Tacitus does, it is true, refer to the eight Batavian cohorts, who play such an important part in the events of 69, as auxilia quartae decimae legionis, but no other passage can be quoted in the same sense, and the connexion in this case was obviously neither close nor durable.[140] In the comparatively detailed account of the first campaign of Bedriacum, which rests at any rate upon a good military source, there is no suggestion that the auxilia marched or manœuvred in separate groups, each connected with a particular legion. Certainly in the normal order of battle throughout the first century the available auxilia were all massed together either as a first line, or in two flanking divisions to the right and left of the legionaries, and the auxilia of the army which crossed the Rhine in 73 were not divided among the legionary legati, but had a commander of their own.[141]

Supporters of the legionary connexion also refer to the two diplomata issued in the same year and on the same day (August 14, 99) to two different groups of auxiliary regiments stationed in Moesia Inferior, and suggest that this curious arrangement can best be explained on the supposition that each diploma refers only to the auxilia of one legion.[142] A similar explanation suggests itself for the fact that only one regiment is common to the two British diplomata of 103 and 105.[143] It seems impossible, however, to interpret all the diplomata in this manner. The British diploma of 124, for example, which was issued to men from six alae and twenty-one cohorts, can hardly be supposed to contain the auxilia of only one of the three legions then stationed in the province.[144] In Pannonia Superior also so many regiments are common to the five complete second-century diplomata which we possess that we must, on this theory, refer them all to the auxilia of one and the same legion.[145] How, then, do we account for the fact that the inscriptions of the province hardly mention any regiments but those contained in these diplomata? In other words, why should all our evidence refer to the auxilia of one legion, and those attached to the other two, then stationed in the province, have entirely disappeared?

A stronger argument is perhaps to be found in inscriptions which contain the phrase legio … et auxilia eius.[146] It could be wished that these texts were more numerous and more precise, but they support the supposition that some connexion existed between each legion and a definite group of auxiliary regiments better than any evidence previously adduced. The connexion, however, must have been very slight and easily broken. Dr. Hardy has pointed out that although three out of the four legions stationed in Germania Superior in 70 left the province for good during the following thirty-five years, there is abundant evidence that nothing like the same proportion of the auxilia stationed in the province accompanied them.[147] It is also clear that, in the second century at any rate, the number of auxilia attached to any legion was not fixed in accordance with any general principle, but depended upon the exigencies of the local situation on each frontier. A reference to the list of provincial garrisons contained in the appendix will show that whereas there are not likely to have been more than three thousand auxilia apiece to each of the three legions of Pannonia Superior, there were probably thirty thousand to be divided among the three legions of Britain, while in Dacia there was only one legion with something approaching twenty-five thousand auxilia. Still, with these reservations, it seems possible enough that the auxilia were always considered as in some sense dependent on the legions, and that where several legions were stationed in the same province, an arrangement was made dividing the auxilia into a corresponding number of groups, each of which was for certain purposes attached to a particular legion.[148]