THE AUXILIA DURING THE FIRST TWO CENTURIES A.D.
SECTION I
THE STRENGTH AND ORGANIZATION OF THE AUXILIARY REGIMENTS
From the death of Augustus to the period when the frontier defences first began to collapse under the strain of the barbarian invasions, more than two centuries later, the imperial army presents a picture of military conservatism unrivalled in history. Not only does the original distinction between the legions of cives Romani and the auxilia of peregrini remain throughout the basis of its organization, but even individual corps show a marvellous power of vitality. Dio Cassius, writing at the beginning of the third century, notes that, of the twenty-five legions in existence in 14, eighteen still survived in his own day, and epigraphical evidence shows that scores even of the more easily destructible auxiliary regiments could claim as long a record. In appearance, indeed, the only considerable change introduced into the organization of the auxilia during this period was the addition of the numeri in the second century to the alae and cohortes which had previously been the only units employed. It is true, of course, that this conservatism was in some respects rather superficial, and that, while administrative forms and nomenclature remained unaltered, in more essential matters the army had been deeply affected by the tendencies of the age. It is still, however, possible, while paying due attention to these changes, to treat the two centuries which follow the death of Augustus as a single period in the history of the auxilia; it is only amid the confusion caused by the barbarian invasions of the third century and the subsequent attempts at reorganization that we definitely lose sight of our old landmarks.
Leaving out of account for the moment the numeri, which, as late creations with a special significance, are reserved for future discussion, let us commence with the alae and cohortes, which remained throughout this period the units of auxiliary cavalry and infantry respectively.
Both these terms, although their history is widely different, originate in the military terminology of the Republic. The term cohors had been originally applied to the infantry contingents of the Italian socii, which were not united in legions after the model of the levies of cives Romani, and it was naturally retained after the disappearance of the socii to describe the similar tactical units of provincial auxilia.
The term ala originated as a metaphorical description of the two divisions into which the contingents of socii were formed, which were stationed in the normal republican order of battle on either flank of the legions. After the disappearance of the socii the term was applied in a more restricted sense to the two flanking divisions in which the average Roman general massed all his available cavalry. This use of the word continued down to the last days of the Republic. When, for instance, the author of the De bello Africo writes, ‘Caesar alteram alam mittit qui satagentibus celeriter occurreret,’[34] or Cicero says of his son in the De Officiis, ‘Quo tamen in bello cum te Pompeius alteri alae praefecisset, magnam laudem et a summo viro, et ab exercitu consequebare equitando, iaculando …’[35] the word is clearly being used in this sense, and does not refer to a regiment of any fixed size. In fact the cavalry of the socii never seem to have been organized in larger units than turmae, and the auxiliary levies naturally adopted the same formation. It has already been noticed that some of the Spanish auxiliaries who served in the Social War are officially described as belonging to a turma Salluitana. Occasional phrases in Livy, such as the statement that the Aetolian cavalry contingent, in the campaign of 171 B.C., was alae unius instar, do not seem to prove anything more than that the historian used the technical terms of his own age to make his narrative clearer.[36] This usage, however, shows that Livy was familiar with the restricted meaning of the word—that is to say, the ala must have been a recognized institution in the reign of Augustus, and we may add that Velleius states that fourteen alae were employed in the Pannonian campaigns of 6-9 in which he himself had served.
It is improbable, however, that the ala was a creation of Augustus, although he may have determined its exact size and organization. In Caesar’s account of his Gallic campaigns we find frequent mention of contingents of tribal cavalry serving as independent units under officers bearing the title of praefecti equitum,[37] and these units must have been much larger than turmae. The organization of these regiments, originally of a purely temporary kind, must have been placed on a more permanent basis when many of them were taken out of their own country to serve in the Civil Wars, and it would have been natural that a new term should be used to describe them.[38]
Evidence in support of this conjecture, which is, as we have seen, lacking in the writings of Caesar and his continuators, has been sought for elsewhere. The majority of Caesar’s praefecti equitum seem to have been tribal chiefs; one may cite, for example, the Aeduan Dumnorix,[39] the heroic veteran Vertiscus,[40] and the two treacherous Allobroges, Roucillus and Egus, the sons of Adbucillus.[41] On the other hand, when we meet with an ala Scaevae on an early inscription, it is difficult to avoid agreeing with Mommsen that it was called after Caesar’s well-known officer of that name.[42] Many other cavalry regiments, which are shown by epigraphical evidence to have existed at an early date and to have been Gallic in composition, bear titles similarly formed from personal names.[43] It is suggested that these corps, or at any rate the majority of them, represent tribal contingents embodied by Caesar at the time of the Civil Wars under the title of alae and placed under his veteran officers. Thus during this period the use of the term ala in the restricted sense would be already known, although only the older and wider use appears in literature. How slowly the new expression won favour is shown by the fact that during the reigns of Augustus and Tiberius the officers commanding these regiments were usually described on inscriptions simply as praefectus equitum, and it was not until after this that the title praefectus alae came to be generally adopted.[44]
Curiously enough, we find very few cohorts with titles which suggest a similar history.[45] Probably in this case Augustus’s reorganization was more thorough and the existing regiments had not, like some of Caesar’s corps of Gallic cavalry, a record of individual achievement which might exempt them from its scope.
Size of regiments. In discussing the size of the auxiliary regiments we have two questions to settle, the numbers of the establishment and the actual strength at which the regiments were maintained. As regards the first question, the evidence of Hyginus[46] and the inscriptions shows us that both alae and cohortes were known as miliariae or quingenariae—that is to say, they contained, roughly speaking, 500 or 1,000 men each. The smaller unit seems to have been preferred in the first century, while the larger predominates among the corps raised by Trajan and his successors. The exact theoretical size, both of the regiments themselves and of the centuries and turmae into which they were divided, is more difficult to determine. Hyginus states that an ala quingenaria was divided into sixteen turmae, and an ala miliaria into twenty-four.[47] He does not state the number of men in a turma in either case, and it seems impossible to arrive at any certainty on the basis of figures found elsewhere in his treatise. Turning to epigraphical evidence we find an inscription from Coptos which describes the composition of a vexillatio drawn from three alae and seven cohorts, as: ‘Alarum III: dec(uriones) V, dupl(icarius) I, sesquiplic(arii) IIII, equites CCCCXXIIII. Cohortium VII: centuriones X, eq(uites) LXI, mil(ites) DCCLXXXIIX’.[48] Von Domaszewski suggests that the cavalry in this detachment are to be divided into ten turmae of 42 men, each commanded by a decurio, a duplicarius, or a sesquiplicarius, and that this figure represents the theoretical strength of the turma in an ala miliaria.[49] In an ala quingenaria, on the other hand, the turma probably contained only 30 men.
This seems to be as near certainty as we are likely to arrive in the present state of our evidence, unless indeed we take literally a statement of Arrian that an ala contained 512 men, a total which would presumably give 32 men to the turma.[50] Arrian is, of course, the best authority on the imperial army whom we possess, but the remark in question is a parenthesis inserted into an account of the ideal establishment of a Hellenistic army, and he may have meant no more than that the unit under discussion corresponded roughly with a Roman ala quingenaria. More satisfactory and conclusive evidence will perhaps be found when the barracks of an ala in a frontier fort have been accurately planned.[51]
The size of the auxiliary cohorts is a matter of even greater difficulty. Hyginus states, and there seems no reason to doubt his statement, that a cohors miliaria was divided into ten centuries, a cohors quingenaria into six.[52] Archaeological evidence supports this statement and suggests further that the centuries were in each case of the same size, since the centurial barracks in the fort at Housesteads, in Northumberland, which was occupied by a cohors miliaria, offer almost precisely the same accommodation as those in the Scottish fort at Newstead, which are clearly designed to accommodate two cohortes quingenariae. The question to be decided is whether these centuries contained 80 or 100 men each. In either case, one of the titles must be a misnomer, since six centuries of 100 would make a cohors quingenaria consist of 600 men, while ten centuries of 80 would only give 800 men for a cohors miliaria. On the whole, although Hyginus suggests the higher figure, the lower is probably to be preferred. Certainly the Coptos inscription cited above, which is probably the most valuable evidence which we possess, clearly indicates centuries of 80. The most important evidence on the other side is that of Josephus, who describes some cohorts which belonged to the Syrian army in 67 A.D. as containing ἀνὰ χιλίους πεζούς.[53] His succeeding statement, however, that other cohorts, by which cohortes equitatae quingenariae are apparently meant, contained 600 infantry and 120 cavalry, suggests that he may be basing his reckoning simply on the number of centuries. Few would defend his calculation in the second instance, and he may be equally wrong in the first. On the whole, therefore, it seems safer to assume establishments of 480 and 800 men for cohortes quingenariae and miliariae respectively, although it remains, of course, possible that the size of the cohorts was altered between the Jewish war of 66-70 and the period of the erection of those frontier forts upon which we have been relying for our evidence.
The last question to be settled in this connexion is that of the cohortes equitatae, in which a proportion of the men were mounted, which form a peculiar and interesting feature of the imperial army. Corps in which infantry and cavalry fought together had of course always been common,[54] but the idea was probably revived by the Romans from observing the practice of the German tribes, from whom Julius obtained a contingent accustomed to fight in this manner.[55] It is certainly significant that one of the earliest of these regiments known to us from inscriptions is a cohors Ubiorum.[56] There is, however, no later evidence for the employment of these tactics, and the continued use of cohortes equitatae is due rather to the necessity of having detachments of mounted men at as many frontier stations as possible. The equites cohortales should be reckoned rather as mounted infantry than cavalry, since we learn from a fragment of Hadrian’s address to the army in Africa that they were worse mounted than the equites alares, and less skilled in cavalry manœuvres.[57] As regards the strength of these regiments and the proportion of mounted to unmounted men, Hyginus states that the cohors miliaria equitata contained 760 infantry and 240 cavalry, while the cohors quingenaria contained six centuries, and in other respects, ‘in dimidio eandem rationem continet’—that is to say, it apparently had 380 infantry and 120 cavalry.[58] The figures for the mounted men are probably correct, and, since we learn from an inscription that there were four decurions to a cohors quingenaria, we may presume that the turmae were 30 strong.[59] This agrees very well with the Egyptian vexillation cited above, which included 61 equites cohortales—that is to say, 2 turmae. On the other hand, there is considerable reason for supposing that the figures for the infantry are schematic and incorrect. It is sufficient here to remark that centuries of 76 could not be divided into contubernia of either 8 or 10, and that the 380 men of Hyginus’s cohors quingenaria could not even be divided evenly among six centuries. The question cannot be settled with certainty until forts occupied by regiments of this class have been planned, but it seems probable that while the number of the centuries remained unaltered the complement of each was reduced from 80 to 60, or possibly to 64, if it was thought desirable to retain the division into contubernia of 8.[60]
Having endeavoured to determine the theoretical establishment of the auxiliary regiments, it remains to discover how far this corresponded to the actual strength at which they were maintained, and here our evidence is scanty, and likely to remain so. Fortunately, the discovery in Egypt of some of the official papers of the Cohors I Augusta Praetoria Lusitanorum has thrown some light on the question. On January 1, 156, this regiment had on its books 6 centurions, 3 decurions, 114 mounted infantry, 19 camel-riders (dromedarii), and 363 infantry, making, with the praefectus, a total of 506 men. Between January and May, 18 recruits were enrolled, 15 infantry, an eques, a dromedarius, and a decurion.[61] These figures agree fairly well with the arrangement suggested above, although the dromedarii are an additional complication, and the regiment appears even to have exceeded its ‘paper-strength’. This, however, may be easily accounted for if we imagine that a number of men had served their term and were about to be discharged. Unfortunately, this document remains isolated, and further evidence is not likely to be forthcoming.
Conditions of service. Questions concerning the method of enlistment for the auxiliary regiments are reserved, on account of their connexion with the broader issues raised by the whole recruiting system, for discussion in a later section. For the present it will be sufficient to discuss the conditions of service in this branch of the army, as they are laid down in the so-called diplomata militaria.[62] These documents, of which we possess some 70 or 80 examples dealing with the auxilia, are small bronze tablets, issued originally to individual soldiers, recording the privileges granted to them either after their discharge or after they had completed a term of 25 years. The reason for this variation seems to be that while the praemia militiae were always conferred after the regulation number of years had been served, it was often the practice to retain the men with the colours for some years longer before finally discharging them. This practice, which we hear of in the early empire as a standing grievance of the legionaries,[63] seems to have prevailed also among the auxilia during the first century.[64] After 107, however, we have no instances of the praemia unpreceded by discharge, a change which is probably due to the perfection of organization, and can be traced also in the legions.
Previous to the reign of Antoninus Pius, the privileges granted to the recipient of a diploma include citizenship for himself, the full legalization of any matrimonial union into which he has entered or shall enter in the future (conubium), and civic rights for his wife, children, and descendants. If he already possessed a family, the names of his wife and children follow his own on the diploma, and the frequency of this occurrence shows the extent to which the military authorities permitted the soldiers to form family ties while on active service.[65] The significance of this fact and its effect on the character of the army will be discussed in a later section.
At the beginning of the reign of Antoninus Pius, a change takes place in that part of the formula which concerns the grant of citizenship. In place of the words ipsis liberis posterisque eorum civitatem dedit et conubium cum uxoribus, &c., we read in all the later examples, civitatem Romanam, qui eorum non haberent, dedit et conubium cum uxoribus, &c.[66] The first inference to be drawn from this alteration is that there now existed a numerous group of auxiliary soldiers who possessed the civitas before their discharge, and we are probably justified in the further inference that many actually possessed it when they were enrolled. It has been noted, for example, that on a document dating from the reign of Trajan, six recruits accepted for the Cohors III Ituraeorum all have the tria nomina.[67] In this change, then, we have a clear instance of the extent to which the franchise was now diffused throughout the Empire.
The omission of the phrase liberis posterisque eorum, on the other hand, suggests the opposite tendency. It cannot, of course, mean that children born after their father’s discharge would not be cives, for their status would be secured by the grant of conubium, but it seems clear that those born before it no longer acquired the citizenship with him. This is supported not only by the absence of all mention of children on the later diplomata,[68] but by the phraseology of an Egyptian document dealing with an ἐπίκρισις of the year 148 which distinguishes two classes of veterans, ἔνειοι μὲν ἐπιτυχόντες σὺν τέκνοις καὶ ἐγγόνοις, ἕτεροι μόνοι τῆς Ῥωμαίων ποτειτείας (sic) καὶ ἐπιγαμίας πρὸς γυναῖκας ἃς τότε εἶχον, ὅτε τούτοις ἡ πολιτεία ἐδόθη,[69] &c. Clearly we have here a translation of both types of formula, and the translator gave to the second the same meaning as that suggested above. Clearly, too, the change was considered an important one since the veterans discharged before and after it are thus divided into two groups. In view of the prevailing policy of the imperial government with respect to the extension of the civitas this step has a curiously retrograde appearance, and it is difficult to see the motives which suggested it. Possibly it was merely desired to get rid of an anomalous situation by which the auxiliaries had previously occupied a more privileged position than the Household Troops.[70] In any case, even after this restriction, there can be little doubt that the grant of the civitas with the improvement in civil status which it brought to the recipient, and the increased possibilities which it offered to his children, must have done much to popularize the service. We have seen that the idea of such a reward did not originate with the Empire, but it was probably not until the reorganization of the army by Augustus that it was regularly conferred and the years of service required to earn it definitely fixed.[71]
We do not know whether at the time of their discharge the auxiliaries also received, like the legionaries, a grant of money or land in lieu of a pension. It seems certain that their status excluded them from a share in the donativa, which the emperors distributed among the troops at their accession, and on other special occasions, and that they could only receive the dona militaria after a special preliminary grant of the civitas.[72] That such grants were made, even to whole regiments at a time, is shown by the number of cohorts which commemorate the receipt of this honour by employing the title civium Romanorum.
On the still more important matter of the ordinary pay of the auxiliary regiments an almost equal uncertainty prevails. Our only two pieces of evidence on the subject, a passage in Tacitus and a phrase in Hadrian’s address to the garrison of Africa,[73] tell us nothing more than that the equites cohortales were paid on a higher scale than the infantry, but received in their turn less than the equites alares, a preference in favour of the mounted men, which is not so great as appears at first sight, since it is clear that they were responsible for the upkeep of their own horses. The chief defect of these passages is that they do not mention the amount of the pay in any of the three cases. Our only basis for calculation is the fact that a legionary considered it promotion to be made duplicarius alae; hence the pay of an ordinary cavalryman must have been more than half that of a legionary. On a priori considerations it can hardly have been less, if, as Hadrian’s speech suggests, he paid for his own arms and mount, and if he also, like the legionaries, had the cost of his rations deducted from his pay. On the whole, however, it seems best to defer speculation until further evidence is forthcoming.[74]
Internal organization. As is only natural in the case of a professional army with so long a term of service, the internal organization of the auxiliary regiments reveals a far more complicated system of grades and promotions than anything which the ancient world had yet known. The epigraphical evidence is abundant, and the efforts of modern scholars, particularly von Domaszewski in his monumental treatise, Die Rangordnung des römischen Heeres, have done much to make the main lines of the system clear. Difficulties in detail still remain, but we may hope for their ultimate solution.
The commanding officer of an ala quingenaria or miliaria, or of a cohors quingenaria bore the title of praefectus. Cohortes miliariae and the cohortes civium Romanorum, which occupied an exceptional position,[75] were commanded by tribuni. Early inscriptions also mention a subpraefectus alae and a subpraefectus cohortis, but these posts seem later to have been abandoned.[76] In later times in case of the absence of the praefectus, his place seems to have been filled by an officer placed temporarily in charge with the title of praepositus or curator. Questions concerning the order of precedence among the praefecti and tribuni, and their place in the military hierarchy generally, are so closely connected with the method of selection and appointment of these officers at different periods, that they are best left for future discussion.[77] It is only important here to note that they usually entered the service with this rank, and that it is very rare to find the regular commander either of an ala or cohort drawn from among the lower officers.
The remaining ‘commissioned officers’, as we should call them, are represented by the troop and company commanders, the decurions who commanded the turmae of the ala, and the centurions and decurions of the cohorts. The senior officer in each class was styled decurio princeps or centurio princeps,[78] but apart from this we cannot trace any regular order of precedence with fixed titles such as is found among the legionary centurions. As regards the respective position of infantry and cavalry officers, the decurio alae ranked highest. This is shown clearly, as von Domaszewski has pointed out, by the frequent employment of this officer as praepositus cohortis.[79] On the other hand, among the officers of the cohorts the centurions ranked above the decurions who commanded the mounted men, where such existed. In one inscription, which seems to have included all the officers of a cohors equitata, the centurions come first on the list, and in the Coptos inscription, so often cited, the officers of the 61 equites cohortales are not mentioned at all.[80] The difference in rank cannot, however, have been very great since all these officers could be promoted to the post of legionary centurion without any intervening step, although this distinction seems to have been conferred most freely upon the decurions of the alae. In these cases it was of course necessary for the auxiliary officer to have acquired the civitas either by serving his full time or by a special grant before his promotion.
Throughout the period these posts seem usually to have been filled by promotion from the lower ranks, although we also find instances of legionaries being given commissioned rank in the auxiliary regiments, and it is officers of this class who seem most frequently to have secured further promotion to the legionary centurionate.[81] Von Domaszewski wishes to consider that these transfers were especially characteristic of the early days of the imperial army, and that a deliberate attempt was then made to provide every auxiliary regiment with a staff of ex-legionaries. With this suggestion, however, it is difficult to agree; not only is the epigraphical evidence insufficient to prove such a wholesale use of imported officers, but the cases known to us are by no means confined to the first fifty years of the Empire. Further, as will be shown later, the arrangement does not harmonize with the general character of the early auxilia.
The holders of subordinate posts, who ranked below the centurion or decurion, may be divided, following the arrangement adopted by von Domaszewski, into two groups.[82] The members of the first group practically correspond to our non-commissioned officers, and are able to command small detachments or to take the place, if necessary, of the company officers. These alone, and the holders of certain higher administrative posts, to which the taktische Chargen gave access,[83] have a legitimate claim to the title of principales. The members of the second group did not, strictly speaking, rank above the privates, but they were granted freedom from certain routine duties in return for special services which they discharged, and were distinguished in consequence by the title of immunes.
It is of course often difficult to ascertain whether a particular post falls into the higher or lower group, and this is especially the case with the standard-bearers, who occupy a position of peculiar importance in the military system. In the ala each troop had its own flag carried by the signifer turmae, but there seems also to have been a regimental standard, the bearer of which was known as the vexillarius alae.[84] A few inscriptions also mention an imaginifer, but it is not clear whether this officer always or at all periods found a place on the staff.[85] In a cohort, on the other hand, each century seems to have had its signifer, and each turma of mounted men its vexillarius, but it does not appear that there was a regimental standard, any more than there existed at this date a standard for each cohort of a legion. This at least is implied by Tacitus in his description of the entry of the Vitellian army into Rome, when he mentions the alarum signa by the side of the legionum aquilae, but says nothing of the ensigns of the cohorts.[86] We must suppose, then, that the imaginifer cohortis, who is mentioned on inscriptions, was not regarded as the regimental standard-bearer any more than the imaginifer legionis.[87]
In consequence of this difference in organization the company and troop standard-bearers of the cohorts rank among the principales, while in the alae only the regimental standard-bearer is included in the higher group, and the signiferi turmae sink to the position of immunes.
Returning, then, to the ala we may place at the head of the principales the vexillarius, and next to him the imaginifer, when this officer existed. Other members of this class were the non-commissioned officers of every turma, the duplicarius and sesquiplicarius,[88] who derived their titles from the fact that they were paid twice and one and a half times the private’s pay respectively, an institution found in the Hellenistic military system from which it was probably borrowed.[89] Lastly we should perhaps add the optio, who commanded the escort of the praefectus (singulares).[90]
To the lower group, the immunes, belong the signifer, custos armorum, and curator attached to every turma,[91] the cornicularius,[92] actarius,[93] strator,[94] stator,[95] librarius,[96] and beneficiarius,[97] who form the clerical and administrative staff of the praefectus, and his escort, the singulares.[98] In determining the position of the holders of these posts among the immunes we are supported by the analogy of the Equites Singulares Imperatoris, a corps modelled upon and to a certain extent recruited from the auxiliary cavalry. The list of a turma of this regiment contained on a Roman inscription gives the following arrangement:[99]
nomina turmae
Iul(ius) Mascel(lus) dec(urio)
Nonius Severus dup(licarius)
Iul(ius) Victorinus sesq(uiplicarius)
Aur(elius) Mucatral
Aur(elius) Lucius
Ael(ius) Crescens sig(nifer)
Aur(elius) Victor arm(orum custos)
Aur(elius) Atero cur(ator)
Ael(ius) Victor bf (beneficiarius)
Cl(audius) Victorinus lib(rarius)
Iul(ius) Vindex bf (beneficiarius)
17 names of equites follow.
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]
Total number of the auxilia. This section should naturally conclude with some statement of the total number of auxilia in the imperial service. Unfortunately, no clear and direct evidence can be obtained on this point either from literary or epigraphical sources. Tacitus, in his survey of the military resources of the Empire in the reign of Tiberius, after enumerating the legions in detail, contents himself with a vague sentence suggesting that the auxiliaries were as numerous as the legionaries and Household Troops.[149] This phrase is perhaps accurate enough for the period to which he is referring, but it is obviously not meant to be precise, and must certainly not be taken to express any principle habitually followed in the composition of the imperial army. If we endeavour to check the statement from other sources we have the remark of Velleius that in 6, at the time of the great Pannonian revolt, the ten legions concentrated under Tiberius’s command were accompanied by 70 cohorts and 14 alae.[150] If we allow for a few regiments being miliariae, this would represent a little over 50,000 men, a number about equivalent to that of the legionaries. If we may assume a similar ratio in other provinces, the total for the auxilia at this period would amount to 150,000 men.[151] It must be remembered, however, that at this date and throughout the whole pre-Flavian period the government relied upon the troops of the client kingdoms and levies of border militia to supplement the imperial troops. With the gradual elimination of these secondary forces, which has already been described, the number of regular units was proportionately increased. More than twenty regiments were raised in the old kingdom of Thrace after its annexation in 46, and five alae and nineteen cohorts are found in 69 garrisoning the two provinces which had been formed from the kingdom of Mauretania.[152] We need not, then, be surprised if the figures supplied by Tacitus and Josephus show that so early as 69 the number of the auxiliaries considerably exceeds the figure suggested for the end of the reign of Augustus. According to Josephus, Vespasian entered Judaea in 67 with at least 20,000 auxiliaries, which probably represents two-thirds of the total number available in the Eastern provinces.[153] In the Danubian provinces in 69 there were, according to Tacitus, sixteen alae.[154] On the basis of the information given in the diplomata, we can safely reckon that there would be at least three cohorts to every ala, and that one regiment in four would be miliaria. Some 40,000 auxiliaries, therefore, must have been stationed in the Danubian provinces at this period. In the same year Vitellius entered Rome with twelve alae and thirty-four cohorts, that is to say some 30,000 men, which represented probably two-thirds of the auxilia in the Rhine armies and Raetia.[155] The garrison of the two Mauretanias, to which allusion has already been made, would amount to about 15,000 men. We thus arrive at the following totals for the auxilia at this period:
| The Eastern provinces | 30,000 | men |
| The Danubian provinces | 40,000 | „ |
| Germany and Raetia | 45,000 | „ |
| The two Mauretanias | 15,000 | „ |
| 130,000 | „ |
To this at least another 50,000 men must be added for the auxilia of Britain, Spain, Africa, Noricum, and the small garrisons of the inland provinces, making a grand total of 180,000 men. The next forty years saw the figure mount even higher. The remaining client kingdoms in the East, which were still strong enough to furnish 15,000 men for the Jewish war in 67, were annexed, and the appearance of several new units with the titles Flavia or Ulpia shows that more than this number of regular auxilia was raised in their place.[156] Even Hadrian seems to have made a few additions to the list, since his foreign policy, though essentially pacific, was based upon a system of frontier defence to which the auxilia were more than ever essential.[157] In Appendix I, where the evidence as to the strength and distribution of the auxilia in the second century is discussed in detail, it is suggested that by the middle of the second century the force may have amounted to some 220,000 men, and that even this figure was probably exceeded sixty years later.