Auxiliaries (Roman military) edit extracted from Wikipedia, the Free Encyclopedia (using Wikipedia Reflection Script)

This article is part of the series on: Military of ancient Rome (portal) 800 BC – AD 476
Structural history
Roman army (unit types and ranks, legions, auxiliaries, generals)
Roman navy (fleets, admirals)
Campaign history
Lists of wars and battles
Decorations and punishments
Technological history
Military engineering (castra, siege engines, arches, roads)
Personal equipment
Political history
Strategy and tactics
Infantry tactics
Frontiers and fortifications (limes, Hadrian's Wall)
This box: view • talk •

Auxiliaries (from Latin: auxilia = "supports") formed the standing non-citizen corps of the Roman army of the Principate (30 BC–284 AD), alongside the citizen legions. By the 2nd century, the auxilia contained the same number of infantry as the legions and in addition provided almost all the Roman army's cavalry and more specialised troops (especially light cavalry and archers). The auxilia thus represented three-fifths of Rome's regular land forces at that time. Like their legionary counterparts, auxiliary recruits were mostly volunteers, not conscripts.

Auxiliary troops were mainly recruited from the peregrini, i.e. free provincial subjects of the Roman Empire who did not hold Roman citizenship and constituted the vast majority of the empire's population in the 1st and 2nd centuries (ca. 90% in the early 1st century). Auxiliaries also included some Roman citizens and probably barbarians (barbari, as the Romans called peoples located outside the Empire's borders). This was in contrast to the legions, which admitted Roman citizens only.

The auxilia developed from the varied contingents of non-Italian troops, especially cavalry, that the Roman Republic used in increasing numbers to support its legions after 200 BC. The Julio-Claudian period (30 BC–68 AD) saw the transformation of these motley temporary levies into a standing corps of regiments with standardised structure, equipment and conditions of service. By the end of this period, there were no significant differences between legionaries and most auxiliaries in terms of training, or thus combat capability.

Auxiliary regiments were often stationed in provinces other than the province in which they were originally raised, to increase the process of romanisation and unification of the provinces into a single empire. The regimental names of many auxiliary units persisted into the 4th century, but by then the units in question were different in size, structure, and quality from their predecessors.

Historical development

Roman Republic (to 30 BC)

Roman auxiliary infantry crossing a river, probably the Danube, on a pontoon bridge during the Dacian Wars (101–106 AD). They can be distinguished from legionaries by their oval shields. Trajan's Column, Rome

The core of the Roman republic's fighting machine was the manipular legion, which was a heavy infantry unit adapted to close-quarter engagements on more or less any terrain probably adopted sometime during the Samnite Wars (343–290 BC).¹ But the legion had a number of deficiencies, especially a lack of cavalry. Around 200 BC, a legion of 4,200 infantry had a cavalry arm of only 300 horse (just 7% of the total force).² This was because the class of citizens who could afford to pay for their own horse and equipment – the equestrian order, the second rank in Roman society, after the senatorial order – was small. In addition the legion lacked missile forces such as slingers and archers.³

Until 200 BC, the bulk of a Roman army's cavalry was provided by Rome's regular Italian allies (socii), commonly known as the "Latin" allies, which made up the Roman military confederation. This was Rome's defence system until the Social War of 91–88 BC. The Italian forces were organised into alae (literally: "wings", because they were generally posted on the flanks of the Roman line of battle). An allied ala, commanded by three Roman praefecti sociorum, was similar or slightly larger in infantry size (4–5,000 men) to a legion, but contained a more substantial cavalry contingent: 900 horse, three times the legionary contingent. Since a pre-Social War consular army always contained an equal number of legions and alae, 75% of its cavalry was provided by the Latin allies. The overall cavalry element, however, remained modest: a normal consular army of two legions and two alae contained ca. 17,500 infantry and 2,400 cavalry (ca. 12% of the total force).⁴ This compares with the overall 21% cavalry component that was typical of the Principate army (80,000 cavalry out of 380,000 total effectives in early the 2nd century).⁵⁶

The Roman/Latin cavalry was sufficient while Rome was in conflict with other states in the mountainous Italian peninsula, which also disposed of limited cavalry resources. But as Rome was confronted by enemies that deployed far more powerful cavalry elements, such as the Gauls and the Carthaginians, the Roman deficiency in cavalry resulted in heavy defeats. The dangers were shown during the sporadic major invasions of Italy by the Gauls. The decisive turning point was the Second Punic War (218–202 BC). Hannibal's major victories at the Trebia and at Cannae, were owed to his Spanish and Gallic heavy cavalry, which far outnumbered the Roman and Latin levies, and to his Numidians, light, fast cavalry which the Romans wholly lacked.⁷ The decisive Roman victory at Zama in 202 BC, which ended the war, owed much to the Numidian cavalry provided by king Massinissa, which outnumbered the Roman/Latin cavalry fielded by 2 to 1.⁸ From then, Roman armies were always accompanied by large numbers of non-Italian cavalry: Numidian light cavalry and, later, Gallic heavy cavalry. For example, Caesar relied heavily on Gallic and German cavalry for his Conquest of Gaul (58–51 BC).⁹

As the role of native cavalry grew, that of Roman/Latin cavalry diminished. In the early 1st century BC, Roman cavalry was phased out altogether. After the Social War, the socii were all granted Roman citizenship, the Latin alae abolished, and the socii recruited into the legions.¹⁰ Furthermore, Roman equestrians were no longer required to perform cavalry service after this time.¹¹ The late Republican legion was thus probably bereft of cavalry (a tiny cavalry force of 120 men was probably added back to the legion under Augustus).¹²

By the outbreak of the Second Punic War, the Romans were remedying the legion's other deficiencies by using non-Italian specialised troops. Livy reports Hiero of Syracuse offering to supply Rome with archers and slingers in 217 BC.¹³ From 200 BC onwards, specialist troops were hired as mercenaries on a regular basis: sagittarii (archers) from Crete, and funditores (slingers) from the Balearic Isles almost always accompanied Roman legions in campaigns all over the Mediterranean.¹⁴

The main other sources of non-Italian troops in the late Republic were subject provincials, allied cities and Rome's amici (satellite kings). During the late Republic, non-Italian units were led by their own native chiefs, and their internal organisation was left to their own commanders. The units varied widely in dress, equipment, and weapons. They were normally raised for specific campaigns and often disbanded soon afterwards, in a similar manner to the earlier socii militia legions.¹⁵

Rule of Augustus (30 BC–14 AD)

At the end of the civil war period (31 BC), it appears that not all indigenous units were disbanded. Some of the more experienced units were kept in being to complement the legions, and became the core of the standing auxiliary forces that developed in the Julio-Claudian period.¹⁶ During the early rule of Augustus (27 BC onwards), the corps of regular auxilia was created. It was clearly inspired by the Latin forces of the pre-Social War Republic, as a corps of non-citizen troops parallel to the legions. But there were fundamental differences, the same as between Republican and Augustan legions. The Latin forces of the Republic were made up of part-time conscripts in units that would be raised and disbanded for and after particular campaigns. The Augustan auxilia were all-volunteer professionals serving in permanent units.¹⁷

The unit structure of the auxilia also differed from the Latin alae, which were like legions with a larger cavalry arm. Augustus however organised the auxilia into regiments the size of cohorts (a tenth the size of legions), due to the much greater flexibility of the smaller unit size. Further, the regiments were of three types: ala (cavalry), cohors (peditata) (infantry) and cohors equitata (mixed cavalry/infantry).¹⁸

The evidence for the size of the Augustus' new units is not clearcut, with our most precise evidence dating to the 2nd century, by which time the unit strengths may have changed. Cohortes were likely modelled on legionary cohorts i.e. six centuriae of about 80 men each (total about 480 men).¹⁹ Alae were divided into turmae (squadrons) of 30 (or 32) men, each under a decurio (literally: "leader of ten").²⁰ This title which derives from the old Roman cavalry of the pre-Social War republic, in which each turma was under the command of three decuriones).²¹ Cohortes equitatae were simply infantry cohortes with a cavalry contingent of four turmae added.²²

Auxiliary regiments were now led by one praefectus (prefect), who could be either a native nobleman, who would probably be granted Roman citizenship for the purpose (e.g. the famous German war leader Arminius gained Roman citizenship probably by serving as an auxiliary prefect before turning against Rome); or a Roman, either of equestrian rank, or a senior centurion.²³

At the start of Augustus' sole rule (30 BC), the original core auxiliary units in the West were composed of warlike tribesmen from the Gallic provinces (especially Gallia Belgica, which then included the regions later separated to form the provinces Germania Inferior and Germania Superior), and from the Illyrian provinces (Dalmatia and Illyricum. By 19 BC, the Cantabrian and Asturian Wars were concluded, leading to the annexation of northern Hispania and Lusitania. Judging by the names of attested auxiliary regiments, these parts of the Iberian peninsula soon became a major source of recruits. Then the Danubian regions were annexed: Raetia (annexed 15 BC), Noricum (16 BC), Pannonia (9 BC) and Moesia (6 AD), becoming, with Illyricum, the Principate's most important source of auxiliary recruits for its entire duration. In the East, where the Syrians already provided the bulk of the Roman army's archers, Augustus annexed Galatia (25 BC) and Judaea: the former, a region in central Anatolia with a Celtic-speaking people, became an important source of recruits. In N. Africa, Egypt, Cyrene, and Numidia (25 BC) were added to the empire. Numidia (modern day Eastern Algeria) was home to the Mauri, the ancestors of today's Berber people. Their light cavalry (equites Maurorum) was highly prized and had alternately fought and assisted the Romans for well over two centuries: they now started to be recruited into the regular auxilia. Even more Mauri units were formed after the annexation of Mauretania (NW Algeria, Morocco), the rest of the Berber homeland, in 44 AD by emperor Claudius (ruled 41–54).²⁴

Recruitment was thus heavy throughout the Augustan period, with a steady increase in the number of units formed. By 23 AD, there were roughly the same numbers of auxiliaries in service as there were legionaries.²⁵ Since at this time there were 25 legions of ca. 5,000 men each, the auxilia thus amounted to ca. 125,000 men, implying ca. 250 auxiliary regiments.²⁶

Illyrian revolt (6–9 AD)

During the early Julio-Claudian period, many auxiliary regiments raised in frontier provinces were stationed in or near their home provinces, except during periods of major crises such as the Cantabrian Wars, when they were deployed temporarily in theatre. This carried the obvious risk if their own tribe or ethnic group rebelled against Rome (or attacked the Roman frontier from outside the Empire), auxiliary troops could be tempted to make common cause with them. The Romans would then be faced by an enemy that included units fully equipped and trained by themselves, thus losing their usual tactical advantages over tribal foes.²⁷

Arminius (Hermann in modern German) is the classic example at an individual level: after several years of serving in Rome's forces as prefect of an auxiliary unit, he used the military training and experience he had gained to lead a confederacy of German tribes against Rome, culminating in the destruction of three Roman legions in the Teutoberg Forest in 9 AD, and the abandonment of Augustus' strategy of annexing Germany as far as the Elbe river. (This strategy was never revived by later emperors).²⁸

At a collective level, the risk was even greater, as the hugely dangerous Illyrian revolt proved. The central Illyrian tribes were tough and spartan shepherds of the Bosnian mountains and excellent soldier-material. Their territory formed part of the strategic province of Illyricum, recently expanded to include the territory of the Pannonii, an Illyrian tribe based on the west bank of the Danube who were subjugated by Rome in 12–9 BC. By the start of the Common Era, they were an important recruitment base for the auxilia.²⁹ But discontent was festering among the Illyrian tribes due to what they saw as the rapacity of Roman tax officials.³⁰ In 6 AD, several regiments of Dalmatae, a warlike Illyrian tribe, were ordered to gather in one place to prepare to join Augustus' stepson and senior military commander Tiberius in a war against the Germans. Instead they mutinied at the assembly point, and defeated a Roman force sent against them.³¹ The Dalmatae were soon joined by the Breuci, another Illyrian tribe that supplied several auxiliary regiments. They gave battle to a second Roman force from Moesia. They lost, but inflicted heavy casualties.³² The rebels were now joined by a large number of other Illyrian tribes. The Dalmatae attacked Salona and overran the Adriatic coast, defeating a Roman force and exposing the Roman heartland of Italy to the fear of a rebel invasion.³³

Augustus ordered Tiberius to break off operations in Germany and move his main army to Illyricum.³⁴ When it became clear that even Tiberius' forces were insufficient, Augustus was obliged to raise a second task force under Tiberius' nephew Germanicus, resorting to the compulsory purchase and emancipation of thousands of slaves to find enough troops, for the first time since the aftermath of the Battle of Cannae two centuries earlier.³⁵ The Romans had now deployed no less than 15 legions and an equivalent number of auxilia.³⁶ Ths amounts to a total of ca. 150,000 men. It included at least 50 auxiliary cohorts composed, exceptionally, of Roman citizens. These were men whose status or background was regarded by Augustus as unsuitable for recruitment into the legions: either natural-born citizens of the lowest category including vagrants and convicted criminals, or the freed slaves (Roman law accorded citizenship to the freed slaves of Roman citizens). These special units were accorded the title civium Romanorum ("of Roman citizens", or c.R. for short. After the Illyrian revolt, these cohorts remained in being and recruited non-citizens like other auxiliary units, but retained their prestigious c.R. title).³⁷³⁸ In addition, the regular forces were assisted by a large number of allied troops from neighbouring Thracia deployed by their king Rhoemetalces, a Roman amicus (puppet king).³⁹

The Romans faced further reverses on the battlefield and a savage guerrilla war in the Bosnian mountains.⁴⁰ It took them three years of hard fighting to quell the revolt, which was described by the Roman historian Suetonius as the most difficult conflict faced by Rome since the Punic wars two centuries earlier.⁴¹ Tiberius finally quelled the revolt in 9 AD. This was just in time: that same year Arminius destroyed Varus' three legions in Germany. The Roman high command was in no doubt that Arminius would have formed a grand alliance with the Illyrians.⁴²

Despite the gravity of this rebellion, the Illyrians went on to become the backbone of the Roman army. By the 2nd century, with roughly half the Roman army deployed on the Danube frontier, the auxilia and legions alike were dominated by Illyrian recruits. In the 3rd century, Illyrians largely replaced Italians in the senior officer echelons of praefecti of auxiliary regiments and tribuni militum of legions. Finally, from 268 to 379 AD, virtually all emperors, including Diocletian and Constantine the Great were Romanised Illyrians from the provinces of Dalmatia, Moesia Superior and Pannonia. These were members of a military aristocracy, outstanding soldiers who saved the empire from collapse in the turbulent late 3rd century.⁴³

Later Julio-Claudians (14–68 AD)

Significant development of the auxilia appears to have taken place during the rule of the emperor Claudius (41–54 AD). A minimum term of service of 25 years was established, at the end of which the retiring auxiliary soldier, and all his children, were awarded Roman citizenship.⁴⁴ This is deduced from the fact that the first known Roman military diplomas date from the time of Claudius. This was a folding bronze tablet engraved with the details of the soldier's service record, which he could use to prove his citizenship.⁴⁵ Claudius also decreed that prefects of auxiliary regiments must all be of equestrian rank, thus excluding centurions from such commands.⁴⁶ The fact that auxiliary commanders were now all of the same social rank as most tribuni militum, (military tribunes, a legion's senior staff officers, all of whom only one, the tribunus laticlavius, was of the higher senatorial rank), probably indicates that auxilia now enjoyed greater prestige. Indigenous chiefs continued to command some auxiliary regiments, and were probably granted equestrian rank for the purpose. It is also likely that auxiliary pay was standardised at this time, but we only have estimates for the Julio-Claudian period.⁴⁷

Auxiliary uniform, armour, weapons and equipment were probably standardised by the end of the Julio-Claudian period. Auxiliary equipment was broadly similar to that of the legions (see Section 2.1 below for possible differences in armour). By 68 AD, there was little difference between most auxiliary infantry and their legionary counterparts in equipment, training and fighting capability. The main difference was that auxilia contained combat cavalry, both heavy and light, and other specialised units that legions lacked.⁴⁸

Claudius annexed to the empire three regions that became important sources of auxiliary recruits: Britannia (43 AD), and the client kingdoms of Mauretania (44) and Thracia (46). The latter became as important as Illyria as a source of auxiliary recruits, especially cavalry and archers. Britain in mid-2nd century contained the largest number of auxiliary regiments in any single province: about 60 out of about 400 (15%).⁴⁹ By the rule of Nero (54–68), auxiliary numbers may have reached, by one estimate, about 200,000 men, implying about 400 regiments.⁵⁰

Revolt of the Batavi (69–70 AD)

Rhine frontier of the Roman empire, 70 AD, showing the location of the Batavi in the Rhine delta region. Roman territory is shaded dark.

They were a warlike people, skilled horsemen, boatmen and swimmers. They were therefore excellent soldier-material. In return for the unusual privilege of exemption from tributum (direct taxes on land and heads that most peregrini were subject to), they supplied a disproportionate number of recruits to the Julio-Claudian auxilia: one ala and eight cohortes. They also provided most of Augustus' elite personal bodyguard unit (Germani corpore custodes), which continued in service until 68 AD. The Batavi auxilia amounted to about 5,000 men, implying that for the entire Julio-Claudian period, over 50% of all Batavi males reaching military age (16 years) may have enlisted in the auxilia.⁵¹ Thus the Batavi, although just about 0.05% of the total population of the empire (of ca. 70 million^{citation needed}) in 23 AD, supplied about 4% of the total auxilia i.e. 80 times their proportionate share.⁵² They were regarded by the Romans as the very best (fortissimi, validissimi) of their auxiliary, and indeed all, their forces.⁵³ In Roman service, they had perfected a technique for swimming across rivers wearing full armour and weapons.⁵⁴

Julius Civilis (clearly an adopted Latin name, not his native one) was a hereditary prince of the Batavi and the prefect of a Batavi cohort. A veteran of 25 years' service, he had distinguished himself by service in Britain, where he and the eight Batavi cohorts had played a crucial role in both the Roman invasion in 43 AD and the subsequent subjugation of southern Britain.⁵⁵

By 69, however, Civilis, the Batavi regiments and the Batavi people had become utterly disaffected with Rome. After the Batavi regiments were withdrawn from Britain to Italy in 66, Civilis and his brother (also a prefect) were arrested by the governor of Germania Inferior on false suspicion of treason. His brother was executed, and Civilis sent to Rome in chains for judgement by Nero.⁵⁶ He was released by Nero's successor, Galba, but the latter also disbanded the imperial bodyguard unit, thus alienating several hundred crack Batavi troops, and indeed the whole Batavi nation who regarded it as a grave insult.⁵⁷ At the same time, relations collapsed between the Batavi cohorts and the legion they had been attached to since the invasion of Britain 25 years earlier (XIV Gemina): their mutual hatred erupted in open fighting on at least two occasions.⁵⁸

At this juncture, the Roman empire was convulsed by its first major civil war since the Battle of Actium exactly a century earlier. The governor of Germania Inferior, ordered to raise more troops, outraged the Batavi by attempting to conscript more Batavi than the maximum stipulated in their treaty. The brutality and corruption of the Roman recruiting centurions (including incidents of sexual assault on Batavi young men) brought already deep discontent in the Batavi homeland to the boil.⁵⁹

Civilis now led his people in open revolt. Initially, he claimed he was supporting his friend from British days Vespasian's bid for power. But the uprising soon became a bid for independence.⁶⁰ Civilis took advantage of the fact that some legions were absent from the Rhine area due to the civil war, and the rest under-strength. In addition, the Roman commanders and their rank-and-file soldiers were divided by loyalty to rival emperors.⁶¹ Civilis quickly won the support of the Batavi's neighbours and cousins, the Cananefates, who in turn won over the Frisii. First the rebel allies captured two Roman forts in their territory, and a cohort of Tungri defected to Civilis.⁶² Then two legions sent against Civilis were defeated when their companion Batavi ala defected to his side.⁶³ The classis germanica (Rhine flotilla), largely manned by Batavi, was seized by Civilis.⁶⁴ Then a further eight Batavi regiments joined him, defeating a Roman force that attempted to thwart them.⁶⁵ By now, Civilis commanded at least 6,000 (12 regiments) of Roman-trained and equipped auxiliary troops (as well as a much larger number of tribal levies). A number of German tribes from beyond the Rhine joined his cause.⁶⁶ Several other German and Gallic units sent against him deserted, as the revolt spread to the rest of Gallia Belgica, including the Tungri, Lingones and Treviri tribes.⁶⁷ He was able to destroy the two remaining legions in Germania Inferior (V Alaudae and XV Primigenia).⁶⁸

By this stage Rome's entire position on the Rhine and even in Gaul was imperiled. Their civil war over, the Romans mustered a huge task force of eight legions (five despatched from Italy, two from Spain and one from Britain) to deal with Civilis.⁶⁹ Its commander Petillius Cerialis had to fight two difficult battles, at Trier and Xanten, before he could overrun the Batavi's homeland.⁷⁰ Tacitus' surviving narrative breaks off as he describes a meeting on an island in the Rhine delta between Civilis and Cerialis to discuss peace terms.⁷¹ We do not know the outcome of this meeting or Civilis' ultimate fate. But in view of his former friendship with Vespasian, who had already offered him a pardon, and the fact that the Romans still needed the crack Batavi troops, it is likely that the terms were lenient by Roman standards.⁷²

Petilius Cerialis took a number of reconstituted Batavi units with him to Britain, and the Batavi regiments continued to serve with special distinction in Britain and elsewhere for the rest of the 1st century and beyond.⁷³ Even as late as 395, units with the Batavi name were classified as elite palatini e.g. equites Batavi seniores (cavalry) and auxilium Batavi seniores (infantry).⁷⁴

Flavian era (69–96 AD)

Tombstone of the eques alaris Titus Flavius Bassus, son of Mucala of the Thracian Dentheletae (Dansala) tribe. He was probably a Roman citizen (since he had served the required term), although unusually his adopted Roman tribal name is not specified (unless the letters M, A, and C of his father's name are supposed to double as an abbreviation of the tribe Maecia). He belonged to the Ala Noricorum (originally raised from the Taurisci tribe of Noricum). He died at age 46 after 26 years' service. The arrangement of the scene, rider spearing a barbarian (the Thracian Hero), indicates that Bassus was a Thracian. He has Romanised names, adopting the names of the emperor Titus Flavius (r. 79–81). Römisch-Germanisches Museum, Cologne, Germany

Roman auxiliary troops defend a fortified position against attacking Dacians. Detail from Trajan's Column, Rome. Early 2nd century

The revolt of the Batavi appears to have led to a significant change in the Roman government's policy on auxiliary deployment. The revolt proved that in times of civil strife, when legions were far from their bases campaigning for rival claimants to the imperial throne, it was dangerous to leave provinces in the hands of auxiliary regiments recruited from the indigenous nation. During the Julio-Claudian period, auxiliary regiments had often been deployed away from their original home province.⁷⁵ But in the Flavian period (69–96), this appears to have become standard policy.⁷⁶ Thus in 70 AD five reconstituted Batavi regiments (one ala and four cohortes) were transferred to Britain under Petillius Cerialis, who had suppressed the Civilis revolt and then embarked on the governorship of the island.⁷⁷ The great majority of regiments probably founded in the first century were stationed away from their province of origin in the second e.g. of 13 British regiments recorded in mid 2nd century, none were stationed in Britain.⁷⁸ Furthermore, it appears that in the Flavian era native nobles were no longer permitted to command auxiliary units from their own nation.⁷⁹

After a prolonged period in a foreign province a regiment would become assimilated, since the majority of its new recruits would be drawn from the province in which it was stationed, or neighbouring provinces.⁸⁰ Those same "British" units, mostly based on the Danube frontier, would by ca. 150, after almost a century away from their home island, be largely composed of Illyrian, Thracian and Dacian recruits. However, there is evidence that a few regiments at least continued to draw some recruits from their original home provinces in the 2nd century e.g. Batavi units stationed in Britain.⁸¹

The Flavian period also saw the first formation of large, double-size units, both infantry and cavalry, of a nominal strength of 1,000 men (cohors/ala milliaria), though they were actually mostly smaller (720 for an ala milliaria and 800 for a cohors milliaria).⁸² These were the mirror image of the double-strength first cohorts of legions also introduced at this time. Such units remained a minority of the auxilia: in mid-2nd century, they constituted 13% of units, containing 20% of total manpower.⁸³

Later Principate (97–284)

Roman cavalry spatha, a longer sword (median blade length: 780 mm [30.7 in]), designed to give the rider a longer reach than the gladius⁸⁴

In 106 AD, emperor Trajan finally defeated the Dacian kingdom of Decebalus and annexed it as the Roman province of Dacia Traiana. By mid 2nd century, there were 44 auxiliary regiments stationed there, about 10% of the total auxilia. In Britain there were 60. Together these two provinces contained about a quarter of the total auxiliary regiments.⁸⁵

At the midway point in this period, there were probably about 380 auxiliary regiments (ca. 90 alae and 290 cohortes, of which about 200 equitatae) . At this time, the auxilia probably numbered a total of about 220,000 effectives i.e. nearly twice the strength in 23 AD. Of the total, about 150,000 were infantry, about 75,000 cavalry.⁸⁶ This compares with 154,000 legionaries (28 legions of 5,500 men each) at this time, of which just 3,360 were cavalry. (See section 4: Auxilia deployment in the 2nd century, below).

During the second half of the 2nd century, the Roman army underwent considerable further expansion, with the addition of five new legions (27,500 men) to a peak of 33.⁸⁷ An equivalent number of auxilia (i.e. 50–60 new regiments) were probably added, perhaps reaching a peak of ca. 440 regiments by the end of Septimius Severus's rule (211 AD).⁸⁸

The likely growth of the Roman auxilia may be summarised as follows:

NOTE: Figures are based on official (not actual) unit strengths and exclude Roman Navy effectives and barbarian foederati.

During the 2nd century some units with the new names numerus ("group") and vexillatio ("detachment") appear in the diploma record.¹⁰² Their size is uncertain, but was likely smaller than the regular alae and cohortes. Some older scholars see these names as specifically denoting the irregular foederati, ethnic units outside the regular auxilia (see section 2.4 Irregular units, below). But the present consensus is that they were part of the regular auxiliary organisation.¹⁰³

In 212, the constitutio Antoniniana (Antonine decree) of emperor Caracalla granted Roman citizenship to all the free inhabitants of the Empire – the peregrini – thus abolishing their second-class status.¹⁰⁴ But there is no evidence that the citizens-only rule for legions was also abolished at this time. The legions simply gained a much wider recruitment base, as they were now able to recruit any male free resident of the empire. Auxiliary units were now recruited mainly from Roman citizens, but probably continued to recruit non-citizen barbari from outside the Empire's borders.¹⁰⁵ However, the citizens-only rule for legions appears to have been dropped some time during the 3rd century, as by the 4th century Romans and barbarians are found serving together in all units.¹⁰⁶

In the mid to late 3rd century, the army was afflicted by a combination of military disasters and of pestilence, the so-called third century crisis. In 251–271 Gaul, the Alpine regions and Italy, the Balkans and the East were simultaneously overrun by Alamanni, Sarmatians, Goths and Persians respectively.¹⁰⁷ At the same time, the Roman army was struggling with the effects of a devastating pandemic, probably of smallpox: the Plague of Cyprian which began in 251 and was still raging in 270, when it claimed the life of emperor Claudius II Gothicus. The evidence for an earlier pandemic, the Antonine Plague (also smallpox) indicates a mortality of 15–30% in the empire as a whole.¹⁰⁸ The armies would likely have suffered deaths at the top end of the range, due to their close concentration of individuals and frequent movements across the empire.¹⁰⁹ This probably led to a steep decline in military numbers, which only recovered at the end of the century under Diocletian (r. 284–305).¹¹⁰

The recruitment shortfall caused by the crisis seems to have led to recruitment of barbarians to the auxilia on a much greater scale than previously. By the 4th century, it has been estimated that some 25% of regular army recruits were barbarian-born. In the elite palatini regiments anywhere between a third and a half of recruits may have been barbarian.¹¹¹ This is likely a much greater proportion of foreigners than joined the auxilia in the 1st-2nd centuries.¹¹² In the 3rd century, a small number of regular auxiliary units appear in the record that, for the first time, bear the names of barbarian tribes from outside the empire e.g. the ala I Sarmatarum attested in 3rd-century Britain.¹¹³ This was probably an offshoot of the 5,500 surrendered Sarmatian horsemen posted on Hadrian's Wall by emperor Marcus Aurelius in ca. 175.¹¹⁴ This unit may be an early example of a novel process whereby irregular units of barbari (foederati) were transformed into regular auxilia. This process intensified in the 4th century: the Notitia Dignitatum, a key document on the late Roman army, lists a large number of regular units with barbarian names.¹¹⁵

Fourth century

In the fourth century, the Roman army underwent a radical restructuring. In the rule of Diocletian (284–305), the traditional Principate formations of legiones, alae and cohortes appear to have been broken up into smaller units, many of which bore a variety of new names.¹¹⁶ Under Constantine I (r. 312–337) it appears that military units were classified into three grades based on strategic role and to some extent quality: palatini, elite units normally part of the exercitus praesentales (imperial escort armies); comitatenses, higher-grade interception forces based in frontier provinces; and limitanei, lower-grade border troops.¹¹⁷ (See Late Roman army).

The old Principate auxilia regiments provided the basis for units at all three grades. The Notitia Dignitatum lists about 70 alae and cohortes that retained their 2nd century names, mostly limitanei.¹¹⁸ But traces of other auxilia regiments can be found in the praesentales and comitatenses armies. For example, many of the new-style auxilia palatina infantry regiments, considered among the best units in the army, were probably formed from old-style auxiliary cohortes, which they appear to closely resemble.¹¹⁹

The late 4th century writer on military affairs Vegetius complains of contemporary young men joining the "auxilia" in preference to the "legions" to avoid the latter's tougher training and duties.¹²⁰ But it is unclear what types of units he was referring to. It is possible that those older terms were still popularly used (misleadingly) to mean limitanei and comitatenses respectively. In any event, his quote in no way describes accurately the Principate auxilia, many of which were of very high quality.¹²¹

Comparison with legions

Auxiliary cavalryman (eques alaris or alarius) with spatha (sword). In addition, he carries a hasta (spear) and oval shield (not visible, over his left shoulder). Note the reconstructed four-horned sella (Roman saddle). This was designed to give a firm seat, to compensate for the absence of stirrups, which were not introduced until the 6th century.¹²²

Legionary foot soldier wielding a gladius, a sword design invented by the Iberian people of pre-Roman Spain. The example shown is of the "Pompeii" type, used from the later 1st century onwards. This was a shorter (median blade length: 460mm [18.1 in]) stabbing-and-slashing sword designed for close combat. On his left hip is just visible his pugio (dagger). The soldier is wearing a chain mail cuirass (lorica hamata) and an "imperial Gallic" type helmet, also prevalent in the late 1st century. He is leaning on his curved rectangular shield (scutum). The armour and weapons of an auxiliary infantryman were identical except that he carried an oval shield (clipeus)¹²³

Roman infantry helmet (Imperial Gallic type), late 1st century. Note (1) reinforcing ridge on the front, to resist downward sword thrusts; (2) wide, hinged cheek-guards to offer maximum facial protection, without covering the front of the face, which would restrict vision, breathing and shouting range; (3) protruding ear-guards to prevent ears being severed, but not covering ears, which would obstruct hearing; (4) angled neck-guard, to prevent chafing against cuirass. Museum Carnuntum, (Austria)¹²⁴

The role of the early Empire auxilia corps vis-a-vis the legions has often been misunderstood. This is ultimately due to the influence of Vegetius, an ancient writer on Roman military doctrine and practices. Vegetius' work De re militari contains much useful information, but it is misleading overall. This is because Vegetius fails to fit his descriptions of army practices into a chronological framework. By his own account, Vegetius' sources stretch three centuries from Cato the Elder in ca. 200 BC to the emperor Hadrian, while he himself wrote two centuries after the latter, when the army was radically different. His work thus contains a jumble of concepts from different eras, largely out of context. Furthermore, not having military experience himself, his understanding of the practical value of the doctrines he espoused was minimal.¹²⁵

Quality and combat capability

Vegetius' comment about young men preferring to join the auxilia in order to escape the harsher discipline and training of the legions is the origin of the view that legionaries were higher quality troops than auxiliaries. The main evidence used to support this view is that legionaries were paid a higher salary. There is no clearcut evidence about the differentials between legionary and auxiliary pay. Outdated scholars suggest pay was as little as one-third of the legionary level. But more recent studies have concluded that the differential was much smaller (just 20% less) and in any case only applied to infantry. Equites cohortales (cohort cavalry) were paid the same as legionaries, and equites alares (ala cavalry) about 20% more.¹²⁶ The legionary's higher pay and valuable bonuses are probably due more to his social superiority as a Roman citizen than to any higher military proficiency. Tacitus' account of the clashes between Batavi auxiliaries and Roman legionaries during the revolt of the Batavi shows that there was no appreciable difference in quality between them.¹²⁷

The view that auxilia were light troops originates from Vegetius' comment that "auxilia are always joined as light troops with the legions in the line".¹²⁸ It is true that some specialist units in the auxilia, such as Syrian archers and Numidian cavalry wore light armour (or none). But they were a small minority of the auxilia. Most auxiliary cohortes contained heavy infantry similar to legionaries.¹²⁹

Much has been made of the clear difference in armour between the two corps shown on Trajan's Column. This is a monument erected in 113 in Rome to commemorate the conquest of Dacia by Emperor Trajan (r. 97–117): its bas-reliefs are a key source for Roman military equipment. Auxilia are generally shown wearing chain mail (lorica hamata) cuirasses or simple leather corslets, and carrying oval shields. Legionaries are depicted wearing laminated-strip armour (lorica segmentata) at all times (whether in combat or in other activities, such as construction) and with curved rectangular shields.¹³⁰ But the figures in Trajan's Column are highly stereotyped, in order to distinguish clearly between different types of troops.¹³¹ On another Trajanic monument, the Adamclisi Tropaeum, the lorica segmentata does not appear at all, and legionaries and auxilia alike are depicted wearing either chain mail or scales (lorica squamata). There is general recognition that the Adamclisi monument is a more accurate portrayal of normality, with the segmentata used rarely, maybe only for combat and parades.¹³² Testing of replica segmentata by reenactors has shown that it is uncomfortable and that chafing makes it painful to wear for more than short periods. On the plus side, it provides more effective protection than the other armour types: it is impenetrable to most arrow or spear strikes.¹³³ It has been argued that the lorica segmentata was used by auxiliaries also. But there is no firm evidence for this. Traces of this type of armour have been found in forts in Raetia from a time when no legions were stationed in the province.¹³⁴ But these may simply have been left behind by legionaries on temporary detachment. Furthermore auxilia are nowhere depicted wearing such armour.¹³⁵

In any event, both corps were equipped with the same weapons: gladius (a close-combat stabbing sword) and javelins, although the type of javelin known as a pilum seems to have been provided to legionaries only.¹³⁶ Goldsworthy points out that the equipment of both corps were roughly equal in weight.¹³⁷ If there was a difference in armour, it was probably due, again, to non-military reasons: by providing legionaries with more protective and expensive armour, the army was highlighting their social superiority, just as it did with higher pay. During the 3rd century, when all peregrini were granted citizenship, and therefore legionaries lost their social superiority, the lorica segmentata and the rectangular shield disappeared.¹³⁸

Auxiliary cohortes (except specialised units) were heavy infantry that fought in the line like the legions. There is no evidence that cohortes fought in a looser order than the legions.¹³⁹ It appears that in a set-piece battle-line, auxiliary infantry would normally be stationed on the flanks, with legionary infantry holding the centre e.g. as in the Battle of Watling Street (60 AD), the final defeat of the rebel Britons under queen Boudicca.¹⁴⁰ This was a tradition inherited from the Republic, when the precursors of auxiliary cohortes, the Latin alae, occupied the same position in the line.¹⁴¹ But the flanks of the line required equal, if not greater, skill to hold as the centre.

Ala cavalry was considered elite.¹⁴² Very little is known about legionary cavalry, but their numbers were so small that they were tactically insignificant. There is no evidence that legions contained archers, and so auxiliary archers (and slingers) were the only missile forces of the Roman army.¹⁴³

Operational autonomy

An auxiliary regiment would normally, but not always, be attached to a legion for operational purposes, with the praefectus under the command of the legatus legionis (the legion's commander). The period that it was so attached could be a long one e.g. the eight Batavi cohortes apparently attached to legion XIV Gemina for the 26 years from the invasion of Britain in 43 AD to the Civil War of 69.¹⁴⁴ But a legion had no standard, permanent complement of auxilia.¹⁴⁵ Its attached auxiliary units were changed and varied in number according to operational requirements at the behest of the legatus Augusti (the governor of the province where the legion was based at the time) or of the emperor in Rome.¹⁴⁶

But the fact that auxiliary regiments were attached to a legion does not imply that they were not capable of, or were not permitted to, carry out operations unaccompanied. Auxiliary regiments were designed as independent formations.¹⁴⁷ Indeed, in view of their lack of significant cavalry or archers, it was the legions which could not easily campaign independently. Examples of major operations carried out by auxilia alone is the campaign against the Iceni tribe in Britain under governor Ostorius Scapula in 47, and the rescue of Brigantian queen Cartimandua in 52.¹⁴⁸ On Trajan's Column, some 20 major battle scenes are shown. Auxilia take part in 19 of these, in 12 of which they are fighting alone, unaccompanied by legionaries.¹⁴⁹

Strategic role

It has been suggested that the auxilia acted as a border defence force, similar to the limitanei troops of the Late Roman army, while the legions acted as a strategic reserve, charged with intercepting major barbarian incursions that the auxilia could not deal with alone. The evidence for this is mixed. In some provinces, e.g. Britain, legionary bases were well behind the frontline. In Britain, the legionary fortresses of Chester and York were over 100 kilometres (62 mi) from Hadrian's Wall. But in other provinces, legions were stationed right on the border: e.g. Regensburg, Vienna and Budapest on the Danube.¹⁵⁰ In Britain, the main responsibility for garrisoning the forts on the Wall and beyond lay with the auxilia. But there is growing evidence that such forts were also garrisoned by legionary detachments, and even by mixed legionary/auxiliary garrisons¹⁵¹

Unit types and structure

Standard unit types

The following table sets out the official, or establishment, strength of auxiliary units in the 2nd century. The real strength of a unit would fluctuate continually, but would likely have been somewhat less than the establishment most of the time.

* tribunus militum in original c.R. cohortes¹⁵³
** praefectus in Batavi and Tungri cohortes milliariae¹⁵⁴

NOTE: Opinion is divided about the size of an ala turma, between 30 and 32 men. 30 was the size of a turma in the Republican cavalry and in the cohors equitata of the Principate auxilia. Against this is a statement by Arrian that an ala was 512 strong.¹⁵⁵ This would make an ala turma 32 men strong.

Recruitment, ranks and pay

Tombstone of Titus Calidius Severus, of the Camilia Roman tribe, an auxiliary trooper who worked his way up from eques (common cavalryman) to decurion of the cohors I Alpinorum (a regiment from the western Alps). He then switched to a legion (presumably after gaining Roman citizenship after 25 of his 34 years of service) and became a centurio of XV Apollinaris (an infantry officer, unless legionary cavalry was officered by centurions also). He died at age 58. Note the portrayal of his chain mail armour, decurion's crested helmet and horse, led by his equerry, probably a slave. This soldier's long career shows that many auxiliaries served longer than the minimum 25 years, and sometimes joined legions. Erected by his brother, Q. Calidius. From Carnuntum, Austria

Tombstone of Marius son of Ructicnus, an auxiliary soldier whose career was less successful than the one above. He never rose above miles (common soldier) in 25 years of service with his regiment, Cohors I Montanorum (originally raised from Raetians of the Julian Alps). Nor, it seems from the absence of a Roman tribal name, did he live to receive his citizenship award, as he died in the final year of the required term. Erected by his heir. 1st century. From Carinthia, Austria

The evidence for auxiliary ranks and pay is scant, even less than the patchy evidence for their legionary counterparts. The available data may be summarised as follows:

* Assuming same pay multiples as equivalent officers in Late Roman army¹⁵⁷

Common soldiers

At the bottom end of the rank pyramid, ordinary soldiers held the official ranks of pedes (foot soldier in a cohors), eques (cavalryman in a cohors equitata) and gregalis (ala cavalryman).¹⁵⁸

During the Principate, recruitment into the legions was restricted to Roman citizens only. This rule, which derived from the pre-Social War Republican army, was strictly enforced. The few exceptions recorded, such as during emergencies and for the illegitimate sons of legionaries, do not warrant the suggestion that that the rule was routinely ignored.¹⁵⁹

In the 1st century, the vast majority of auxiliary common soldiers were recruited from the Roman peregrini (second-class citizens). In the Julio-Claudian era, conscription of peregrini seems to have been practiced alongside voluntary recruitment, probably in the form of a fixed proportion of men reaching military age in each tribe being drafted.¹⁶⁰ From the Flavian era onwards, the auxilia were an all-volunteer force.¹⁶¹ Although recruits as young as 14 are recorded, the majority of recruits (66%) were from the 18–23 age group.¹⁶²

When it was first raised, an auxiliary regiment would have been recruited from the native tribe or people whose name it bore. In the early Julio-Claudian period, it seems that efforts were made to preserve the ethnic integrity of units, even when the regiment was posted in a faraway province. But in the later part of the period, recruitment in the region where the regiment was posted increased and became predominant from the Flavian era onwards.¹⁶³ The regiment would thus lose its original ethnic identity.¹⁶⁴ The unit's name would thus become a mere curiosity devoid of meaning, although some of its members might inherit foreign names from their veteran ancestors. This view has to be qualified, however, as evidence from military diplomas and other inscriptions shows that some units continued to recruit in their original home areas e.g. Batavi units stationed in Britain, where some units had an international membership.¹⁶⁵ It also appears that the Danubian provinces (Raetia, Pannonia, Moesia, Dacia) remained key recruiting grounds for units stationed all over the empire.¹⁶⁶¹⁶⁷

It appears that Roman citizens were also regularly recruited to the auxilia. Most likely, the majority of citizen recruits to auxiliary regiments were the sons of auxiliary veterans who were enfranchised on their fathers' discharge.¹⁶⁸ Many such may have preferred to join their fathers' old regiments, which were a kind of extended family to them, rather than join a much larger, unfamiliar legion. There are also instances of legionaries transferring to the auxilia (to a higher rank).¹⁶⁹ The incidence of citizens in the auxilia would thus have grown steadily over time until, after the grant of citizenship to all peregrini in 212, auxiliary regiments became predominantly, if not exclusively, citizen units.

Less clearcut is the question of whether the regular auxilia recruited barbari (barbarians, as the Romans called people living outside the empire's borders). Although there is little evidence of it before the 3rd century, the consensus is that auxilia recruited barbarians throughout their history.¹⁷⁰¹⁷¹ In the 3rd century, a few auxilia units of clearly barbarian origin start to appear in the record e.g. Ala I Sarmatarum, cuneus Frisiorum and numerus Hnaufridi in Britain.¹⁷²¹⁷³

There existed a hierarchy of pay between types of auxiliary, with cavalry higher paid than infantry. One recent estimate is that in the time of Augustus, the annual pay structure was: eques alaris (gregalis) 263 denarii, eques cohortalis 225, and cohors infantryman 188.¹⁷⁴ The same differentials (of about 20% between grades) seem to have existed at the time of Domitian (r. 81-96).¹⁷⁵ However, Goldsworthy points out that the common assumption that rates of pay were universal across provinces and units is unproven. Pay may have varied according to the origin of the unit.¹⁷⁶

The remuneration of an auxiliary pedes cohortalis may be compared to a legionary's as follows:

Gross salary was subject to deductions for food, clothing, boots and hay (probably for the company mules). It is unclear whether the cost of armour and weapons was also deducted, or borne by the army. Deductions left the soldier with a net salary of 78 denarii. This sum was sufficient, on the basis of the food deduction, to amply feed an adult for a year. In 84 AD Domitian increased basic legionary pay by 33% (from 225 to 300 denarii): a similar increase was presumably accorded to auxiliaries, boosting their net income to 140 denarii, i.e. more than two food allowances.¹⁷⁸ It was entirely disposable, as the soldier was exempt from the poll tax (capitatio), did not pay rent (he was housed in fort barracks) and his food, clothing and equipment were already deducted. It should be borne in mind that most recruits came from peasant families living at subsistence level. To such persons, any disposable income would appear attractive.¹⁷⁹ It could be spent on leisure activities, sent to relatives or simply saved for retirement.

There is no evidence that auxiliaries received the substantial cash bonuses (donativa), handed to legionaries on the accession of a new emperor and other occasions.¹⁸⁰ Although irregular, these payments (each worth 75 denarii to a common legionary) averaged once every 7.5 years in the early 1st century and every three years later. Duncan-Jones has suggested that donativa may have been paid to auxiliaries also from the time of Hadrian onwards, on the grounds that the total amount of donative to the military increased sharply.¹⁸¹ A very valuable benefit paid to legionaries was the discharge bonus (praemia) paid on completion of the full 25 years' service. At 3,000 denarii, this was equivalent to ten years' gross salary for a common legionary after the pay increase of 84 AD. It would enable him to purchase a substantial plot of land. Again, there is no indication that auxiliaries were paid a discharge bonus. For auxiliaries, the discharge bonus was the grant of Roman citizenship, which carried important tax exemptions. However, Duncan-Jones argues that the fact that service in the auxilia was competitive with the legions (deduced from the many Roman citizens that joined the auxilia) that a discharge bonus may have been paid.¹⁸²

Junior officers

Officers in the Roman army were known as principales. Below centurion rank, a cohort's centuriae appear to have the same ranks as legionary centuriae i.e. the group of junior officers: vexillarius (standard-bearer for the whole regiment, from vexillum) optio (the centurion's deputy), signifer (standard-bearer for the centuria) and tesserarius (officer of the watch), in order of rank. In the turmae of cohortes equitatae (and of alae?), the decurion's second-in-command was probably known as a curator, responsible for horses and caparison.¹⁸³ As in the legions, the junior principales, together with some regimental specialists, were classified in two general ranks: duplicarii ("double-pay men") and sesquiplicarii ("one-and-a-half-pay men").¹⁸⁴ These ranks probably compare most closely, in function and pay levels, with the modern junior ranks of sergeant and corporal.

Besides combat effectives, regiments also contained specialists, some of whom held the ranks of duplicarius or sesquiplicarius, others were common soldiers with the status of milites immunes ("exempt soldiers" i.e. exempt from normal duties). Ranking specialists included the medicus (regimental doctor), veterinarius (veterinary doctor, in charge of the care of horses, pack animals and livestock), custos armorum (keeper of the armoury), cornicularius (clerk in charge of all the regiment's records and paperwork).¹⁸⁵

Senior officers

The limited evidence on auxiliary centuriones and decuriones is that such officers could be directly commissioned as well as promoted from the ranks. Many appear to have come from provincial aristocracies.¹⁸⁶ Those rising from the ranks could be promotions from the legions as well as from the unit's own ranks. In the Julio-Claudian period auxiliary centuriones and decuriones were a roughly equal split between citizens and peregrini, though later citizens became predominant due to the spread of citizenship among military families.¹⁸⁷ Because centuriones and decuriones could rise from the ranks, they have often been compared to non-commissioned officers such as sergeants in modern armies. But this comparison certainly undervalues their role and social status. In addition to their military duties, centurions performed a wide range of administrative tasks, which was necessary in the absence of an adequate bureaucracy to support provincial governors. They were also relatively wealthy, due to their high salaries (see below).¹⁸⁸ A mid-level modern officer such as a major is probably a closer parallel. However, most of the surviving evidence concerns legionary centurions and it is uncertain whether their auxiliary counterparts shared their high status and non-military role.¹⁸⁹

We do not know pay rates for centuriones and decuriones, but these are also believed to have amounted to several times that of a miles.¹⁹⁰ In the late Roman army, an officer called a centenarius, which may be the equivalent of the earlier centurio, was paid 2.5 times the salary of a common soldier. His immediate superior, a ducenarius (who according to the unreliable Vegetius commanded 200 men, as the title implies), was paid 3.5 times.¹⁹¹

Unlike a legatus legionis (who had an officer staff of six tribuni militum and one praefectus castrorum), an auxiliary praefectus does not appear to have enjoyed the support of purely staff officers. The possible exception is an attested beneficiarius ("deputy"), who may have been the praefectus' second-in-command, if this title was a regular rank and not simply an ad hoc appointment for a specific task. Also attached to the praefectus were the regiment's vexillarius (standard-bearer for the whole unit) and cornucen (horn-blower).¹⁹²

Commanders

It appears that in the 2nd century, the majority of auxiliary prefects were still of Italian origin.¹⁹³ In contrast, the evidence for the 3rd century is that Italians provided less than a third of prefects.¹⁹⁴ All prefects were members of the equestrian order, either by birth, or by attaining the property qualification (100,000 denarii, the equivalent of 400 years' gross salary for an auxiliary alaris) or by military promotion. The latter were the chief centurions of legions (centurio primus pilus) who would normally be awarded equestrian rank after a year as primuspilus.¹⁹⁵

Equestrians by birth would normally begin their military careers at ca. 30 years of age. Commands were held in a set sequence, each held for 3–4 years: prefect of an auxiliary cohors, tribunus militum in a legion and finally prefect of an auxiliary ala. In Hadrian's time, a fourth command was added, for exceptionally able officers, of prefect of an ala milliaria. Like officers senatorial rank, hereditary equestrians held civilian posts before and after their decade of military service, whereas non-hereditary officers tended to remain in the army, commanding various units in various provinces. By the 3rd century, most auxiliary prefects had exclusively military careers.¹⁹⁶¹⁹⁷

The pay of a praefectus of an auxiliary regiment in the early 2nd century has been estimated at over 50 times that of a miles (common soldier).¹⁹⁸ (This compares to a full colonel in the British Army, who is currently paid about five times a private's salary).