Auxiliaries ( Roman military ) Auxiliaries ( from Latin : auxilia = " helps " ) formed the standing non - citizen corps of the Imperial Roman army during the Principate era ( 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 of 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 ( c . 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 only admitted Roman citizens . 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 , both for reasons of imperial security and to foster the process of Romanisation and integration of the provinces . 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 . Background : Roman Republic ( to 30 BC ) . The mainstay of the Roman republic ' s war machine was the manipular legion , a heavy infantry unit suitable for close - quarter engagements on more or less any terrain , which was probably adopted sometime during the Samnite Wars ( 343 – 290 BC ) . Despite its formidable strength , 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 ) . 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 relatively small . In addition the legion lacked missile forces such as slingers and archers . 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 3 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 , c . 12 % of the total force ( 2 , 400 out of a normal consular army of approximately 20 , 000 total effectives ) , was greater than in most peninsular Italian forces , but well below 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 ) . 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 external enemies that deployed far more powerful cavalry elements , such as the Gauls and the Carthaginians , the Roman deficiency in cavalry numbers could be a serious liability , which in the Second Punic War ( 218 – 202 BC ) resulted in crushing defeats . 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 . 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 . 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 ) . 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 . Furthermore , Roman equestrians were no longer required to perform cavalry service after this time . 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 ) . By the outbreak of the Second Punic War , the Romans were remedying the legions ' other deficiencies by using non - Italian specialised troops . Livy reports Hiero of Syracuse offering to supply Rome with archers and slingers in 217 BC . 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 . 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 . Foundation of the auxilia under Augustus ( 30 BC – 14 AD ) . It appears that not all indigenous units were disbanded at the end of the civil war period ( 31 BC ) . 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 . 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 mainly volunteer professionals serving in permanent units . 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 ) . 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 ) . " Alae " were divided into " turma e " ( squadrons ) of 30 ( or 32 ) men , each under a " decurio " ( literally : " leader of ten " ) . 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 " ) . " Cohortes equitatae " were simply infantry " cohortes " with a cavalry contingent of four " turmae " added . 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 . 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 ) . Additionally , independent auxiliary units were often the only Roman military force present in the " inermes provinciae " , or " unarmed provinces " , such as Mauretania . Recruitment was thus heavy throughout the Augustan period , with a steady increase in the number of units formed . By 23 AD , the Roman historian Tacitus records that there were roughly the same numbers of auxiliaries in service as there were legionaries . Since at this time there were 25 legions of c . 5 , 000 men each , the auxilia thus amounted to c . 125 , 000 men , implying c . 250 auxiliary regiments . 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 . The German leader Arminius 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 ) . 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 , Celticised Illyrian tribes based on the west bank of the Danube who were subjugated by Rome in 12 – 9 BC ( the " Bellum Pannonicum " ) . By the start of the Common Era , they were an important recruitment base for the auxilia . But discontent was festering among the Illyrian tribes , largely due to what they saw as the rapacity of Roman tax officials . In AD 6 , several regiments of Dalmatae , a warlike Illyrian tribe , were ordered to report to a designated location 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 . 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 . The rebels were now joined by a large number of other Illyrian tribes . The Dalmatae attacked the port of Salona and overran the Adriatic coast , defeating a Roman force and exposing the Roman heartland of Italy to the fear of a rebel invasion . Augustus ordered Tiberius to break off operations in Germany and move his main army to Illyricum . 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 over two centuries earlier . The Romans had now deployed no less than 15 legions and an equivalent number of auxilia . This amounts to a total of c . 150 , 000 men , including 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 . In addition , the regular forces were assisted by a large number of allied troops from neighbouring Thrace deployed by their king Rhoemetalces I , a Roman " amicus " ( puppet king ) . The Romans faced further reverses on the battlefield and a savage guerrilla war in the Bosnian mountains . It took them three years of hard fighting to quell the revolt , which was described by the Roman historian Suetonius , writing in ca . AD 100 , as the most difficult conflict faced by Rome since the Punic Wars over two centuries earlier . Tiberius finally succeeded in quelling the revolt in 9 AD . This was apparently lucky timing for the Romans : that same year Arminius destroyed Varus ' three legions in Germany . The Roman high command had no doubt that Arminius would have formed a grand alliance with the Illyrians . Despite the gravity of this rebellion , the Illyrians went on , alongside their neighbours the Thracians , 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 AD 268 to 379 , 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 . 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 . This is deduced from the fact that the first known Roman military diploma s 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 . Claudius also decreed that prefects of auxiliary regiments must all be of equestrian rank , thus excluding centurions from such commands . 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 . 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 specialized units that legions lacked . Claudius annexed to the empire three regions that became important sources of auxiliary recruits : Britannia ( 43 AD ) , and the former 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 % ) . By the rule of Nero ( 54 – 68 ) , auxiliary numbers may have reached , by one estimate , about 200 , 000 men , implying about 400 regiments . Revolt of the Batavi ( 69 – 70 AD ) . The Batavi , a Germanic tribe , inhabited the region today known as Gelderland ( Netherlands ) , in the Rhine river delta , then known as the " Insula Batavorum " ( " Island of the Batavi " , because surrounded by branches of the Rhine ) , part of the Roman province of Germania Inferior . They were a warlike people , skilled horsemen , boatmen and swimmers . In return for the unusual privilege of exemption from " tributum " ( direct taxes on land and heads normally exacted from " peregrini " ) , 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 ( the " Germani corpore custodes " ) , which continued in service until 68 AD . The Batavi auxilia amounted to about 5 , 000 men , implying that during the entire Julio - Claudian period , over 50 % of all Batavi males reaching military age ( 16 years ) may have enlisted in the auxilia . Thus the Batavi , although just 0 . 05 % of the total population of the empire of c . 70 million in 23 AD , supplied about 4 % of the total auxilia i . e . 80 times their proportionate share . They were regarded by the Romans as the very best ( " fortissimi " , " validissimi " ) of their auxiliary , and indeed all , their forces . In Roman service , both their cavalry and infantry had perfected a technique for swimming across rivers wearing full armour and weapons . Julius Civilis ( literally : " Julius the Citizen " , clearly a Latin name adopted on gaining Roman citizenship , 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 . 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 a fabricated accusation of sedition . The governor ordered his brother ' s execution , while Civilis , who as a Roman citizen had the right to appeal to the emperor , was sent to Rome in chains for judgement by Nero . He was released by Nero ' s overthrower and successor , Galba , but the latter also disbanded the imperial bodyguard unit for their loyalty to Nero . This alienated several hundred crack Batavi troops , and indeed the whole Batavi nation who regarded it as a grave insult . At the same time , relations collapsed between the Batavi cohorts and the legion to which they had been attached since the invasion of Britain 25 years earlier ( " XIV Gemina " ) . Their mutual hatred erupted in open fighting on at least two occasions . At this juncture , the Roman empire was convulsed by its first major civil war since the Battle of Actium exactly a century earlier : the Year of the Four Emperors ( 69 - 70 AD ) . 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 . Civilis now led his people in open revolt . Initially , he claimed he was supporting the bid for power of Vespasian , the general in command of the legions in Syria , whom Civilis had probably befriended when both were involved in the Roman invasion of Britain 25 years earlier ( Vespasian was then commander of the legion " II Augusta " ) . But the uprising soon became a bid for independence . Civilis exploited 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 . Civilis quickly won the support of the Batavi ' s neighbours and kinsmen , 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 . Then two legions sent against Civilis were defeated when their companion Batavi " ala " defected to his side . The " Classis Germanica " ( Rhine flotilla ) , largely manned by Batavi , was seized by Civilis . Most importantly , the 8 Batavi cohorts stationed at Mainz with " XIV Gemina " mutinied and joined him , defeating at Bonn a Roman force that attempted to block their return to their homeland . By now , Civilis commanded at least 12 regiments ( 6 , 000 men ) 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 . 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 . He was able to destroy the two remaining legions in Germania Inferior , ( " V Alaudae " and " XV Primigenia " ) . 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 dispatched from Italy , two from Spain and one from Britain ) to deal with Civilis . Its commander Petillius Cerialis had to fight two difficult battles , at Trier and Xanten , before he could overrun the Batavi ' s homeland . 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 . 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 Batavi levies , it is likely that the terms were lenient by Roman standards . 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 . Even as late as 395 , units with the Batavi name , although long since composed of recruits from all over the empire , were still classified as elite " palatini " , e . g . the " equites Batavi seniores " ( cavalry ) and " auxilium Batavi seniores " ( infantry ) . Flavian era ( 69 – 96 AD ) . 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 exclusively 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 . But in the Flavian period ( 69 – 96 ) , this appears to have become standard policy . 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 . The great majority of regiments probably founded in the 1st 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 . Furthermore , it appears that in the Flavian era native nobles were no longer permitted to command auxiliary units from their own nation . 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 . Those same " British " units , mostly based on the Danube frontier , would by c . 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 . 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 " ) . 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 . Later Principate ( 97 – 284 ) . 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 . There is considerable scholarly dispute about the precise size of the auxilia during the imperial era , even during the corp ' s best - documented period , the rule of Trajan ' s successor , Hadrian ( 117 - 138 ) . This is evident if one compares calculations by Spaul ( 2000 ) and Holder ( 2003 ) : In addition , Holder believes that a further 14 " cohortes " , which are attested under Trajan , immediately before Hadrian ' s rule , but not during or after it , probably continued in existence , giving a total of 381 units and 225 , 000 effectives . The discrepancy between the two scholars is due to : ( i ) Interpretation of units with the same name and number , but attested in different provinces in the same period . Spaul tends to take a more cautious approach and to assume such are the same unit moving base frequently , while Holder tends to regard them as separate units which acquired the same number due to duplicated ( or even triplicated ) seriation . ( ii ) Assumptions about how many " cohortes " were " equitatae " . Spaul accepts only those " cohortes " specifically attested as " equitatae " i . e . , about 40 % of recorded units . Holder estimates that at least 70 % of " cohortes " contained cavalry contingents by the early 2nd century Even according to the more conservative estimate , the auxilia were by this time significantly larger than the legions , which contained c . 155 , 000 effectives ( 28 legions of 5 , 500 men each ) at this time , of which just 3 , 360 were cavalry . ( For a detailed breakdown , 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 5 new legions ( 27 , 500 men ) to a Principate peak of 33 . A matching number of auxilia ( i . e . ca . 50 regiments , although only the names of around 25 - 30 have survived in the epigraphic record ) were probably added , possibly reaching a peak of c . 440 regiments and around 250 , 000 effectives by the end of Septimius Severus ' s rule ( 211 AD ) . 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 . Their size is uncertain , but was likely smaller than the regular " alae " and " cohortes " , as originally they were probably detachments from the latter , acquiring independent status after long - term separation . As these units are mentioned in diplomas , they were presumably part of the regular auxiliary organisation . But " numeri " was also a generic term used for barbarian units outside the regular auxilia . ( see section 2 . 4 Irregular units , below ) . 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 . 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 . 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 . In the mid to late 3rd century , the army was afflicted by a combination of military disasters and of pestilence , the so - called Crisis of the Third Century . In 251 – 271 Gaul , the Alpine regions and Italy , the Balkans and the East were simultaneously overrun by Alamanni , Sarmatians , Goths and Persians respectively . 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 . 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 . This probably led to a steep decline in military numbers , which only recovered at the end of the century under Diocletian ( r . 284 – 305 ) . 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 . This is likely a much greater proportion of foreigners than joined the auxilia in the 1st - 2nd centuries . 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 . This was probably an offshoot of the 5 , 500 surrendered Sarmatian horsemen posted on Hadrian ' s Wall by emperor Marcus Aurelius in c . 175 . 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 . 4th century . In the 4th 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 . 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 . ( 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 " . 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 . 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 . 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 . Unit types and structure . Regular 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 . " Cohortes " . These all - infantry units were modelled on the cohorts of the legions , with the same officers and sub - units . It was a common misconception among dated scholars that auxiliary " cohortes " only contained light infantry . Most of the auxiliary infantry were armed in similar fashion as legionaries , with metal helmets and cuirasses ( chain - mail or scale ) , and " gladius " swords . Some auxiliaries may even have been equipped with the " lorica segmentata " , the most sophisticated legionary body - armour , although this disputed by some scholars . There is no evidence that auxiliary infantry fought in a looser order than legionaries . 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 ( AD 60 ) , the final defeat of the rebel Britons under queen Boudicca . This was a tradition inherited from the Republic , when the precursors of auxiliary " cohortes " , the Latin " alae " , occupied the same position in the line . The flanks of the line required equal , if not greater , skill to hold as the centre . " Alae " . During the Principate period of the Roman Empire ( 30 BC – AD 284 ) , the all - mounted " alae " contained the elite cavalry of the army . They were specially trained in elaborate manoeuvres , such as those displayed to the emperor Hadrian during a documented inspection . They were best - suited for large - scale operations and battle , during which they acted as the primary cavalry escort for the legions , which had almost no cavalry of their own . They were heavily protected , with chain - mail or scale body armour , a cavalry version of the infantry helmet ( with more protective features ) and oval shield . Their offensive weapons included a spear ( " hasta " ) , a cavalry sword ( " spatha " ) , which was much longer than the infantry " gladius " to provide greater reach and a long dagger . The elite status of an " alaris " is shown by the fact that he received 20 % greater pay than his counterpart in a cohort , and than a legionary infantryman . " Cohortes equitatae " . These were " cohortes " with a cavalry contingent attached . There is evidence that their numbers expanded with the passage of time . Only about 40 % of attested " cohortes " are specifically attested as " equitatae " in inscriptions , which is probably the original Augustan proportion . A study of units stationed in Syria in the mid 2nd century found that many units which did not carry the " equitata " title did in fact contain cavalrymen e . g . by discovery of a tombstone of a cavalryman attached to the cohort . This implies that by that time , at least 70 % of " cohortes " were probably " equitatae " . The addition of cavalry to a cohort obviously enabled it to carry out a wider range of independent operations . A " cohors equitata " was in effect a self - contained mini - army . The traditional view of " equites cohortales " ( the cavalry arm of " cohortes equitatae " ) , as expounded by G . L . Cheesman , was that they were just a mounted infantry with poor - quality horses . They would use their mounts simply to reach the battlefield and then would dismount to fight . This view is today discredited . Although it is clear that " equites cohortales " did not match " equites alares " ( " ala " cavalrymen ) in quality ( hence their lower pay ) , the evidence is that they fought as cavalry in the same way as the " alares " and often alongside them . Their armour and weapons were the same as for the " alares " . Nevertheless , non - combat roles of the " equites cohortales " differed significantly from the " alares " . Non - combat roles such as despatch - riders ( " dispositi " ) were generally filled by cohort cavalry . Auxiliary specialised units . In the Republican period , the standard trio of specialised auxilia were Balearic slingers , Cretan archers and Numidian light cavalry . These functions , plus some new ones , continued in the 2nd century auxilia . Heavily - armoured lancers . " Equites cataphractarii " , or simply " cataphractarii " for short , were the heavily - armoured cavalry of the Roman army . Based on Sarmatian and Parthian models , they were also known as " contarii " and " clibanarii " , although it is unclear whether these terms were interchangeable or whether they denoted variations in equipment or role . Together with new units of light mounted archers , the " cataphractarii " were designed to counter Parthian ( and , in Pannonia , Sarmatian ) battle tactics . Parthian armies consisted largely of cavalry . Their standard tactic was to use light mounted archers to weaken and break up the Roman infantry line , and then to rout it with a charge by the " cataphractarii " concentrated on the weakest point . The only special heavy cavalry units to appear in the 2nd century record are : " ala I Ulpia contariorum " and " ala I Gallorum et Pannoniorum cataphractaria " stationed in Pannonia and Moesia Inferior respectively in the 2nd century . Light cavalry . From the Second Punic War until the 3rd century AD , the bulk of Rome ' s light cavalry ( apart from mounted archers from Syria ) was provided by the inhabitants of the Maghrebi provinces of Africa and Mauretania Caesariensis , the Numidae or Mauri ( from whom derives the English term " Moors " ) , who were the ancestors of the Berber people of modern Algeria and Morocco . They were known as the " equites Maurorum " or " Numidarum " ( " Moorish or Numidian cavalry " ) . On Trajan ' s Column , Mauri horsemen , depicted with long hair in dreadlocks , are shown riding their small but resilient horses bare - back and unbridled , with a simple braided rope round their mount ' s neck for control . They wear no body or head armour , carrying only a small , round leather shield . Their weaponry cannot be discerned due to stone erosion , but is known from Livy to have consisted of several short javelins . Exceptionally fast and maneuverable , Numidian cavalry would harass the enemy by hit - and - run attacks , riding up and loosing volleys of javelins , then scattering faster than any opposing cavalry could pursue . They were superbly suited to scouting , harassment , ambush and pursuit . It is unclear what proportion of the Numidian cavalry were regular auxilia units as opposed to irregular " foederati " units . In the 3rd century , new formations of light cavalry appear , apparently recruited from the Danubian provinces : the " equites Dalmatae " ( " Dalmatian cavalry " ) . Little is known about these , but they were prominent in the 4th century , with several units listed in the " Notitia Dignitatum " . Camel troops . A unit of " dromedarii " ( " camel - mounted troops " ) is attested from the 2nd century , the " ala I Ulpia dromedariorum milliaria " in Syria . Archers . A substantial number of auxiliary regiments ( 32 , or about 1 in 12 in the 2nd century ) were denoted " sagittariorum " , or archer - units ( from " sagittarii " lit . " arrow - men " , from " sagitta " = " arrow " ) . These 32 units ( of which 4 were double - strength ) had a total official strength of 17 , 600 men . All three types of auxiliary regiment ( " ala " , " cohors " and " cohors equitata " ) could be denoted " sagittariorum " . Although these units evidently specialised in archery , it is uncertain from the available evidence whether all " sagittariorum " personnel were archers , or simply a higher proportion than in ordinary units . At the same time , ordinary regiments probably also possessed some archers , otherwise their capacity for independent operations would have been unduly constrained . Bas - reliefs appear to show personnel in ordinary units employing bows . From about 218 BC onwards , the archers of the Roman army of the mid - Republic were virtually all mercenaries from the island of Crete , which boasted a long specialist tradition . During the late Republic ( 88 - 30 BC ) and the Augustan period , Crete was gradually eclipsed by men from other , much more populous , regions subjugated by the Romans with strong archery traditions . These included Thrace , Anatolia and above all , Syria . Of the 32 " sagittarii " units attested in mid 2nd century , 13 have Syrian names , 7 Thracian , 5 from Anatolia , 1 from Crete and the remaining 6 of other or uncertain origin . Three distinct types of archers are shown on Trajan ' s Column : ( a ) with scalar cuirass , conical steel helmet and cloak ; ( b ) without armour , with cloth conical cap and long tunic ; or ( c ) equipped in the same way as general auxiliary foot - soldiers ( apart from carrying bows instead of javelins ) . The first type were probably Syrian or Anatolian units ; the third type probably Thracian . The standard bow used by Roman auxilia was the recurved composite bow , a sophisticated , compact and powerful weapon . Slingers . From about 218 BC onwards , the Republican army ' s slingers were exclusively mercenaries from the Balearic Islands , which had nurtured a strong indigenous tradition of slinging from prehistoric times . As a result , in classical Latin , " Baleares " ( literally " inhabitants of the Balearic Islands " ) became an alternative word for " slingers " ( " funditores " , from " funda " = " sling " ) . Because of this , it is uncertain whether the most of the imperial army ' s slingers continued to be drawn from the Balearics themselves , or , like archers , derived mainly from other regions . Independent slinger units are not attested in the epigraphic record of the Principate . However , slingers are portrayed on Trajan ' s Column . They are shown unarmoured , wearing a short tunic . They carry a cloth bag , slung in front , to hold their shot ( " glandes " ) . Scouts / Numeri . " Exploratores " ( ' reconnaissance troops ' , from " explorare " = " to scout " ) . Two examples include " numeri exploratorum " attested to in the third century in Britain : " Habitanco " and " Bremenio " ( both names of forts ) . It is possible , however , that more than 20 such units served in Britain . The literal translation of " numeri " is ' numbers ' and it was often used in the context of a generic title for any unit that was not of a standard size or structure . From the second century onward they served as frontier guards , often supplied by the Sarmatians and the Germans . Little else is known about such units . Irregular allied forces . Throughout the Principate period , there is evidence of ethnic units of " barbari " outside the normal auxilia organisation fighting alongside Roman troops . To an extent , these units were simply a continuation of the old client - king levies of the late Republic : " ad hoc " bodies of troops supplied by Rome ' s puppet petty - kings on the imperial borders for particular campaigns . Some clearly remained in Roman service beyond the campaigns , keeping their own native leadership , attire and equipment and structure . These units were known to the Romans as " socii " ( " allies " ) , " symmachiarii " ( from " symmachoi " , Greek for " allies " ) or " foederati " ( " treaty troops " from " foedus " , " treaty " ) . One estimate puts the number of " foederati " in the time of Trajan at about 11 , 000 , divided into about 40 " numeri " ( units ) of about 300 men each . The purpose of employing " foederati " units was to use their specialist fighting skills . Many of these would have been troops of Numidian cavalry ( see light cavalry above ) . The " foederati " make their first official appearance on Trajan ' s Column , where they are portrayed in a standardised manner , with long hair and beards , barefoot , stripped to the waist , wearing long trousers held up by wide belts and wielding clubs . In reality several different tribes supported the Romans in the Dacian wars . Their attire and weapons would have varied widely . The Column stereotypes them with the appearance of a single tribe , probably the most outlandish - looking , to differentiate them clearly from the regular auxilia . Judging by the frequency of their appearance in the Column ' s battle scenes , the " foederati " were important contributors to the Roman operations in Dacia . Another example of " foederati " are the 5 , 500 captured Sarmatian cavalrymen sent by Emperor Marcus Aurelius ( r . 161 – 180 ) to garrison a fort on Hadrian ' s Wall after their defeat in the Marcomannic Wars . Recruitment , ranks and pay . The evidence for auxiliary ranks and pay is scant : even less exists than the patchy evidence for their legionary counterparts . There seems to be some consensus , however , that the auxiliary was paid one third of what a legionary received : 300 sesterces a year ( 400 after the reign of the emperor Commodus ) . Both auxiliaries and seamen received the " viaticum " of 300 sesterces , although the various sources differ as to whether auxiliaries and sailors received the retirement bonus known as the " honesta missio " , or honorable discharge . The available data may be broken down and summarised as follows : Rankers ( " caligati " ) . At the bottom end of the rank pyramid , rankers were known as " caligati " ( lit : " sandal men " from the " caliga e " or hob - nailed sandals worn by soldiers ) . Depending on the type of regiment they belonged to , they held the official ranks of " pedes " ( foot soldier in a " cohors " ) , " eques " ( cavalryman in a " cohors equitata " ) and " gregalis " ( " ala " cavalryman ) . 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 the rule was routinely ignored . In the 1st century , the vast majority of auxiliary common soldiers were recruited from the Roman " peregrini " ( second - class citizen s ) . 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 . From the Flavian era onwards , the auxilia were an all - volunteer force . Although recruits as young as 14 are recorded , the majority of recruits ( 66 % ) were from the 18 – 23 age group . 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 . The regiment would thus lose its original ethnic identity . 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 . It also appears that the Danubian provinces ( Raetia , Pannonia , Moesia , Dacia ) remained key recruiting grounds for units stationed all over the empire . 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 . 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 ) . 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 . 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 . 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 . The same differentials ( of about 20 % between grades ) seem to have existed at the time of Domitian ( r . 81 - 96 ) . 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 . 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 . 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 . 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 ( donativum ) handed to legionaries on the accession of a new emperor and other occasions . 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 at that time . 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 . Junior officers ( " principales " ) . Below centurion / decurion rank , junior officers in the Roman army were known as " principales " . An auxiliary cohort ' s ranks appear the same as in a legionary " centuria " . These were , in ascending order : " tesserarius " ( " officer of the watch " ) , " signifer " ( standard - bearer for the " centuria " ) , " optio " ( centurion ' s deputy ) and " vexillarius " ( standard - bearer for the whole regiment , from " vexillum " ) . 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 . As in the legions , the " principales " , together with some regimental specialists , were classified in two pay - scales : " sesquiplicarii " ( " one - and - a - half - pay men " ) and " duplicarii " ( " double - pay men " ) . These ranks are probably most closely resembled by the modern ranks of corporal and sergeant respectively . Besides combat effectives , regiments also contained specialists , the most senior of whom were " sesquiplicarii " or " duplicarii " , the rest common soldiers with the status of " milities 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 ) , and the " cornicularius " ( clerk in charge of all the regiment ' s records and paperwork ) . 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 . Those rising from the ranks could be promotions from the legions as well as from the regiment ' 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 . Because " centuriones " and " decuriones " often rose from the ranks , they have often been compared to warrant officer s such as sergeants - major in modern armies . However , centurions ' social role was much wider than a modern warrant - officer . 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 table above ) . 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 . There is little evidence about the pay - scales of auxiliary " centuriones " and " decuriones " , but these are also believed to have amounted to several times that of a " miles " . Unlike a " legatus legionis " ( who had an officer staff of 6 " 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 ) . Commanders . It appears that in the 2nd century , the majority of auxiliary prefects were still of Italian origin . In contrast , the evidence for the 3rd century is that Italians provided less than a third of prefects . 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 elevated to equestrian rank by the emperor after completing their single - year term as " primuspilus " . Equestrians by birth would normally begin their military careers at c . 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 . 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 ) . ( This compares to a full colonel in the British Army , who is currently paid about five times a private ' s salary ) . The reason for the huge gap between the top and the bottom of the pyramid is that Roman society was far more hierarchical than a modern one . A " praefectus " was not just a senior officer . He was also a Roman citizen ( which most of his men were not ) and , as a member of the equestrian order , an aristocrat . The social gulf between the " praefectus " and a " peregrinus " soldier was thus immense , and the pay differential reflected that fact . Names , titles and decorations . Regimental names . The nomenclature of the great majority of regiments followed a standard configuration : unit type , followed by serial number , followed by name of the " peregrini " tribe ( or nation ) from whom the regiment was originally raised , in the genitive plural case e . g . " cohors III Batavorum " ( " 3rd Cohort of Batavi " ) ; " cohors I Brittonum " ( " 1st Cohort of Britons " ) . Some regiments combine the names of two " peregrini " tribes , most likely after the merger of two previously separate regiments e . g . " ala I Pannoniorum et Gallorum " ( " 1st Wing of Pannonii and Gauls " ) . A minority of regiments are named after an individual , mostly after the first prefect of the regiment e . g . " ala Sulpicia " ( presumably named after a prefect whose middle ( " gens " ) name was Sulpicius ) . The latter is also an example of regiments that did not have a serial number . Titles . Regiments were often rewarded for meritorious service by the grant of an honorific title . The most sought - after was the prestigious " c . R . " ( " civium Romanorum " = " of Roman citizens " ) title . In the latter case , all the regiment ' s members at the time , but not their successors , would be granted Roman citizenship . But the regiment would retain the c . R . title in perpetuity . Another common title was the " gens " name of the emperor making the award ( or founding the regiment ) e . g . " Ulpia " : the " gens " name of Trajan ( Marcus Ulpius Traianus r . 98 – 117 ) . Other titles were similar to those given to the legions e . g . " pia fidelis " ( " p . f . " = " dutiful and loyal " ) . Decorations . The Roman army awarded a variety of individual decorations ( " dona " ) for valour to its legionaries . " Hasta pura " was a miniature spear ; " phalerae " were large medal - like bronze or silver discs worn on the cuirass ; " armillae " were bracelets worn on the wrist ; and torques were worn round the neck , or on the cuirass . The highest awards were the " coronae " ( " crowns " ) , of which the most prestigious was the " corona civica " , a crown made of oak - leaves awarded for saving the life of a Roman citizen in battle . The most valuable award was the " corona muralis " , a crown made of gold awarded to the first man to scale an enemy rampart . This was awarded rarely , as such a man hardly ever survived . There is no evidence that auxiliary common soldiers received individual decorations , although auxiliary officers did . Instead , the whole regiment was honoured by a title reflecting the type of award e . g . " torquata " ( awarded a torque ) or " armillata " ( awarded bracelets ) . Some regiments would , in the course of time , accumulate a long list of titles and decorations e . g . " cohors I Brittonum Ulpia torquata pia fidelis c . R . " . Deployment in 2nd century . Notes : ( 1 ) Table excludes about 2 , 000 officers ( centurions and above ) . ( 2 ) Auxiliary cavalry nos . assumes 70 % of " cohortes " were " equitatae " Analysis