All you want to know about the Roman army

1. The Roman Army

The army of the empire – the principate.

The power of the Roman emperors rested on their control of massive armed forces, paid for out of the emperor’s privy purse and bound to him by an oath of personal allegiance. The vast majority of soldiers were stationed in so-called imperial provinces, commanded by direct appointees of the emperor. The Roman imperial army was thus in effect very much a private army.

The imperial army was a standing professional army. It contained both conscripts and volunteers serving a minimum term of sixteen years, though most had to serve for 25 years or more before they were up for retirement. To preserve the loyalty of the soldiers on which their position of power rested, the emperors looked well after their interests. Pay was regular and comparatively generous and on occasion supplemented by donativa, special bonuses of up to five years pay. On completion of their term of service soldiers received a large retirement grant of thirteen to seventeen years’ worth of pay. In addition to these monetary rewards serving soldiers and retired veterans were also granted numerous legal privileges.

The army of the empire was like its republican predecessors made up of a variety of different units. The most important divisions were however made between the legions, the auxiliaries, the fleet and the imperial guards. It are these main branches of the armed services that will be briefly discussed below.

The legions

The core of the Roman army was formed by the units called legions from the Latin legio, meaning a levy. During the first three centuries of the empire the army contained no more than 25 to 34 legions. Each of these units consisted of about 5000-6000 men recruited among the citizen body. Although the soldiers of the legion were Roman citizens, this did not imply that they originated from the city of Rome or even Italy. With the spread of the franchise among the population of the conquered territories provincials quickly became the most important source of recruits. Italian levies however remained the most usual source for newly raised legions, although several units were formed using marines or legionaries detached from existing formations.

The legio was a miniature army that contained within its ranks troops trained and equipped to perform all kinds of different duties both on and off the battlefield. Although the vast majority of soldiers served as heavy infantry, other legionaries fought as cavalry, archers or light infantry. Other specialised troops operated artillery consisting of torsion guns. The troops were however not solely prepared for combat. Legionaries regularly served as combat engineers constructing fortifications, roads and bridges. As the legion counted among its complement a vast number of men with special skills it was in many ways self-supporting. A large part of its military equipment could be produced by artisans in the ranks. Soldiers trained as surveyors, engineers and architects ensured that the legion needed little outside help for its building requirements. Administrative duties were performed by other legionaries both within their unit as well as in the provincial bureaucracy.

Each legion carried a number and a name, e.g. legio X Gemina (the tenth ‘twin’ or ‘double’ legion), to which honorary titles like pia fidelis (dutiful and loyal) could be added. The numbering and naming of units followed no rationalised pattern. As many of the formations originated in the various armies of the civil wars following the death of Julius Caesar, several legions carried identical numerals or nicknames. Even new legions that were levied were named and numbered according to diverse systems. The sense of individuality provided by these numbers and titles was reinforced by the use of different unit symbols and signs like bulls, boars or capricorns.

The organisation

The strength and organisation of the legions varied in time and was probably not completely standardised throughout the army. Generally speaking however the legio was organised in ten cohortes or cohorts. These cohorts consisted each of three manipuli, literally ‘handfuls’, which were in their turn subdivided in two centuriae or ‘hundreds’. These centuriae were composed of a number of contubernia or ‘tentparties’. Although the name centuria would seem to indicate a unit of a hundred soldiers, this unit could comprise anything from 30 to over 200 individuals. The usual establishment strength however is thought to have been 80 men. From the second half of the first century AD in at least some of the legions the first cohort was reorganised in five double strength centuriae while the remainder continued to be organised in the old manner.

In addition to the regular organisation of cohortesmanipuli and centuriae of the legionary heavy infantry there were other subunits for the equites legionis, the legionary cavalry, and the antesignani or lancearii, the elite legionary light infantry. The exact details of their organisation are as yet not very clear. For a variety of duties provisional units known as vexillationes or numeri were formed. The strength and organisation of these provisional units varied greatly and was only in part based on the more regular subdivisions of the legion.

The officers

Command of the legion was usually given to a legatus legionis picked by the emperor from the senatorial class who generally had some previous military experience through service as a tribunus. In Egypt and from the start of the third century also in other provinces the command was not entrusted to a senatorial legatus, but to a praefectus legionis, an acting commander drawn from the equestrian order. The legionary commander was assisted by six military tribunes. With the exception of the units stationed in Egypt one of these tribuni was usually a young senator at the start of his public career. Known as a tribunus laticlavius from the broad purple stripes on his tunic this senior tribune was second-in-command. His collegues from the equestrian order were known as tribuni angusticlavii and generally had done earlier service as a commander of an auxiliary infantry unit. A former senior centurion usually performed the duties of praefectus castrorum, camp commandant, and was the third in the chain of command.

The most important officers in the legions were the centuriones. These men were partly directly recruited from the Roman knights or the city councilmembers, but the greater part of the centurions had previously served as soldiers and NCO’s in the legions or the praetorian cohorts. Depending on the organisation of the legion either sixty or fifty nine centuriones ordinarii commanded the centuriae, while a varying number of centuriones supernumerarii were employed for special duties. These officers were known by titles derived from the place of their units in the old battle order. The hastatus prior, princeps prior and pilus prior were the higher ranking officers commanding the manipuli. The hastatus posteriorprinceps posterior and pilus posterior acted as their deputies. The cohorts were under the command of the pilus prior. Distinguished from their fellow officers were the primi ordines, the senior centurions of the first cohort of the legion. These men had achieved their posts by prior service in other postings and were chief advisors of the legionary commanders. The post of primus pilus, the highest ranking centurion in the legion, carried great prestige and assured entry into the equestrian order.

An uncertain number of supernumerary centurions performed a variety of tasks both within the legion itself and in other units. Centuriones exercitatores for example were used as training officers for the legionary cavalry and the horse guards of provincial governors and the emperor. Acenturio stratorum was employed to oversee the remount system of the provincial armies and on occasion to command the singulares, the auxiliary soldiers serving as a governor’s guard. The centuriones lanceariorum led the elite legionary infantry known as antesignani or lancearii. Other supernumerary officers performed duties in the medical service of the legions.

The non-commissioned officers

To assist the officers the legion counted a number of NCO’s among its strength. These men were known as principales and depending on their status received as duplicarii double pay or as sesquiplicarii pay and a half. Each centurio ordinarius had an optio as his deputy. Whereas the centurion led his men from the front, the optio was stationed at the rear of the unit to keep the legionaries from shirking away in combat. The signifer or standard bearer carried the signum of the unit. This standard served both as a rallying point for the soldiers and to communicate simple visual commands to the troops in battle. The task of carrying the signum in battle was dangerous as the soldier had to stand in the first rank and could carry only a small buckler. It may not be strictly coincidental that available epigraphical evidence contains a relatively large number of discentes signiferorum, trainee standard-bearers. The signifer also assumed responsibility for the financial administration of the unit and functioned as the legionaries’ banker. The tesserarius was a third NCO attached to a centuria and in charge of the distribution and collection of the watch words. Both optio and signifer received double pay, but the tesserarius attached to a centuria was on pay and a half. Other principales like the cornicularius were attached to the administrative offices of the legion.

A considerable number of legionary soldiers were classed as immunes. These men were exempted from the more tedious chores because of the special tasks they had to perform, but received no extra pay. As many a soldier without immunity was forced to bribe his centurion to escape the less desirable duties, the immunes would in practice have had some financial gain from their position. Among the immunes were musicians, military police, cavalry troopers, drill and weapons instructors, artisans, clerks and medical orderlies. It was usual for both immunes and principales to have served several years as a munifex, a private liable for all kinds of duty and fatigues, before they received promotion. Most, if not all, positions were reached after a period of specialised training as a discens.

The auxilia

The imperial Roman army continued the republican tradition of supplementing the citizen legions with units recruited from peregrini, non-citizens from conquered or allied communities. In the imperial army the total numerical strength of the various auxiliary formations was roughly comparable to that of the legionary troops. These forces were known as socii or auxilia and were composed of both regular and irregular formations. Many modern works distinguish regular auxilia consisting of cohortes and alae from irregular numeri. This present day division disregards the fact that irregular units could be designated as a cohors and that numerus was a very generic term which was also in general use for regular army units. As in the legiones draftees and volunteers served side by side in the auxiliary forces. With the spread of Roman citizenship among the population of the conquered territories the auxilia were increasingly recruiting citizens into the ranks, blurring the original division between peregrine auxiliaries and citizen legionaries.

The imperial auxilia were composed of a variety of units. Infantry units were generally organised in cohorts that in the case of cohortes equitatae could include a small mounted force. Cavalry was usually formed into alae or ‘wings’. Both cohortes and alae could comprise either quingenaria units of approximately 500 man or milliaria formations of 800-1000 soldiers. Infantry cohorts with a mounted contingent had an additional 120 to 250 cavalry troopers. Infantry cohorts were composed of three to five manipuli of each two centuriae. Cavalry alae counted 16 to 24 turmae of 30-40 mounted soldiers. Auxiliary formations were usually commanded by a praefectus cohortis or praefectus alae, though a tribunus cohortis or legionary centurio was occasionally employed. Some of these commanders were drawn from the tribal aristocracy, though most were recruited from the equestrian order. Command of a cavalry alae was only entrusted to men who had previously served as a praefectus cohortis and legionary tribunus. The infantry subunits had similar officers and NCO’s as their legionary counterparts. Cavalry turmae were placed under a decurio instead of a centurion. Legionaries were regularly transferred to act as officers and NCO’s in the units of the auxilia.

Units in the auxiliary forces carried like the legions a number and a title. The numbering of units followed different patterns and partly reflected the order in which troops had been levied. The names of units varied greatly, many like cohors I Batavorum being derived from the tribe that provided the original levies, others reflecting the armament, e.g. the ala I contariorum, or honouring a former commander, for example ala Siliana. Redeployment of units and the Roman practice of local recruitment of replacements meant that the ethnic titles borne by formations did not reflect the actual origins of its soldiers.

The infantry of the auxilia consisted mainly of soldiers trained and equipped to fight in a way comparable to that of the legionary heavy infantry. In addition to these existed specialised formations of light infantry adept at fighting in a looser order. Units of archers formed a large proportion of the available auxiliary forces. The alae were for the larger part made up of medium cavalry suited for both skirmishing and shock tactics. Formations of mounted archers were also much employed. A minority of the cavalry units were composed of heavy cavalry troopers armed with the contus, a two handed cavalry spear. These soldiers and some of their mounts as well were heavily armoured. In at least part of the medium cavalry alae a number of troopers used to fight as horse archers or heavy cavalry giving the unit a wider range of combat capabilities.

From the auxiliary units of a provincial army a number of soldiers were selected for service in the singulares of the governor’s guard. Infantrymen from the cohorts were grouped in the pedites singulares while horsemen from both cohortes equitatae and alae were brigaded in the equites singulares. Both units were trained and commanded by legionary centuriones. The strength of these guard formations was probably related to the numbers of troops deployed in a province. The fact however that regular army formations like the ala singularium were formed from such elite units seems to indicate a strength of approximately 500 for both infantry and cavalry singulares. As promotions in the Roman army were as much depending on personal relations as on merit, men serving in the governor’s guard could look forward to better army careers.

The service conditions

There is much debate on the actual service conditions enjoyed by soldiers serving in the auxilia. Recently published evidence seems to indicate that basic pay under the principate was either 1/6th part less or even equal to that of the legionaries. Auxiliaries were also included in the occasional distribution of donativa. These similar service conditions help explain why legionary soldiers were transferring freely to posts in auxiliary units. An important service condition for non-citizens enlisted in the auxilia was the grant of Roman citizenship. Generally this was awarded after 25 years of service, though on occasion grants were made during service as a reward for bravery in battle. An additional retirement grant of money for the auxilia is very likely, though the evidence available is ambiguous. The often cited difference in dimensions of the living space between the larger bases of legions and the smaller frontier forts may not have served to accentuate status differences between the legions and auxiliaries. Not only were legionary soldiers regularly stationed in the smaller forts, but the larger forts were also in part garrisoned by units of the auxilia.

The imperial guard

The Roman emperor had several guard units at his disposal. The most important of these were the cohortes praetoriae or praetorian guard. During the reign of the Julio-Claudian dynasty the Germani custodes corporis or German bodyguard provided additional security. From the accession of Traianus the equites singulares Augusti recruited among the auxiliary cavalry formed the emperor’s horse guard. The majority of these men served as guards, i.e. picked troops, rather than bodyguards directly watching over the person of the emperor. These elite forces at the emperor’s immediate disposal formed the nucleus of the field armies assembled for imperial military expeditions. Smaller numbers of soldiers were selected among the guard units for personal protection duties.

The praetorian guard

Under the republic Roman generals had usually formed a guard unit named cohors praetoria after the praetorium or HQ. Under the empire such units became a privilege reserved for the emperor under whose auspicia all military operations were conducted. Augustus originally formed nine numbered cohortes praetoriae consisting of both infantry and cavalry billeted at Rome and some other Italian cities. This number was later raised to ten units and the cohorts were concentrated in a large base adjacent to Rome. Command of the praetorian guard was entrusted to one or two equestrian praefecti praetorio. Three additional cohortes urbanae with a similar structure were also present at Rome, but not under the direct control of the praetorian prefects.

A praetorian cohort consisted of approximately 500 infantrymen organised in manipuli and centuriae and under the overall command of a tribunus. This strength was doubled in the course of the first century AD. The majority of praetorians fought as heavy infantry with smaller numbers acting as light infantry lancearii and archers. Added to these foot soldiers each cohort contained a number of cavalrymen. The combined equites praetoriani numbered at least 400 men and may even have been a thousand strong. Other troopers were known as equites speculatores and served as bodyguards to the emperor. The praetorian cohort that guarded the imperial palace and accompanied the emperor in the city of Rome was known as the cohors togata. As their duties were performed within the pomerium, the sacred boundary of the city, these soldiers could not wear full armour and equipment and therefore dressed in civilian togae, though keeping their swords at hand.

Service conditions in the praetorian cohorts were better than in the legions. Pay was substantially higher and donativa were more frequent. The term of service of sixteen years compared favourably to the 20 to 25 years in the legions. Promotion opportunities were also excellent. A large part of the legionary posts as centurio was filled by former praetorian guardsmen. The cohortes praetoriae recruited originally in Italy and the older coloniae in the provinces, though at times legionaries were transferred to the guard. From the reign of Septimius Severus the transfer of picked legionaries became the usual method of filling the ranks of the praetorian guard.

The praetorian guard originally served as the backbone of field armies assembled for campaigns that involved the emperor, one of his relatives or a praefectus praetorio. Contrary to popular opinion this meant that the Rome based soldiers had a fair chance of being involved in combat either against the barbarians from across the borders or rebellious Roman army units. Despite the increase in the establishment strength of the praetorian cohorts the guards were increasingly complemented by other formations. In the course of the third century AD the cohortes praetoriae in the comitatus, the imperial field army, were regularly supplemented by mobile troops from the legio II Parthica based at Albanum in Italy. Vexillationes of elite legionaries and auxiliaries from the frontier armies joining these core formations in the imperial field army were slowly developing into separate units that were permanently attached to the imperial retinue.

The imperial horse guard

The citizen guardsmen of the praetorian cohorts had their counterpart in the originally non-citizen horse guards. These consisted in the Julio-Claudian era of the Germani custodes corporis disbanded after Nero and the later equites singulares Augusti. Both these units were also known as Batavi after the tribal origin of many imperial horse guards. Members were usually recruited from the alae and cohortes equitatae, though at times men were directly recruited. The centuriones exercitatores or cavalry training officers for the imperial horse guard were however not drawn from the auxilia, but were selected from the legionary cavalry. The strength of the horse guard was approximately a thousand troopers, a number doubled by Septimius Severus. The organisation of the horse guard resembled that of the cavalry in the auxilia with turmae commanded by decuriones. An equestrian tribunus functioned as overall commander of the imperial horse guards.

The fleet

The main function of the classis or fleet was to combat piracy and to support the operations of the other armed services. The imperial navy maintained two larger fleets based in the Mediterranean with smaller squadrons operating on the North Sea, Black Sea and the major rivers. Ravenna and Misenum were the main naval bases in the mare nostrum though ships were regularly detached to other ports. There existed some dedicated fleet installations along the river Rhine and Danube, but most were attached to bases of the frontier armies. The ships used by the imperial navy comprised both oared warships and transports as well as sailing craft used mainly for logistical support.

The vessels of the Roman navy were not manned by the slave rowers of popular imagination. All personnel serving in the imperial fleet were classed as soldiers, regardless of their function. Though the fleet had its own marines, these troops were used for boarding parties rather than amphibious assaults. The status of the sailors and marines of the Roman navy is somewhat unclear, though the fleet is generally regarded as the least prestigious branch of service. The fleet recruited freeborn citizens and peregrini as well as freedmen. Soldiers that did not possess Roman citizenship received this privilege after a minimum of 25 years of service.

A ship’s crew, regardless of its size, was organised as a centuria with one officer responsible for sailing operations and a centurio for the military tasks. Among the crew were usually also a number of principales and immunes, some of which were identical to those of the army and some of which were peculiar to the fleet. Command of fleets was given to equestrian praefecti, those of the fleets based at Ravenna and Misenum having the largest prestige. The total strength of the Roman navy is not known with any exactitude, though it was reportedly some 40.000 strong during the reign of Diocletian. The Ravenna and Misenum fleets were each at least numerous enough to furnish the required number of men for a new legio.

Naval forces were used to create both auxiliary units, the cohortes classiariorum and cohortes classicae, and legionary formations, the legiones I and II Adiutrices. In addition men were also transferred to the auxilia or legiones on an individual basis. The fleet squadrons in at least the Danubian provinces may have received direct support from army units, as there is evidence available that a number of legionary soldiers received training as epibatae or liburnarii for service as marines.

2. The Army of the Dominate

The army of the tetrarchy

The field armies

Under Diocletian the frontier armies bore the brunt of the defence of the empire. The role of the field armies decreased somewhat as political stability meant that usurpations were a lesser threat that they had been before. Each of the tetrarchs had a small sacer comitatus at his disposal. The nucleus of these imperial field armies was formed by guard units and a select number of permanently attached detachments from the provincial armies. For large campaigns these formations were temporarily joined by vexillationes from the frontier forces.

The tetrarchic field armies were made up of a number of different formations. Detachments from the praetorian guards, both infantry and mounted troops like the equites promoti, were permanently attached to the retinue of the emperors. These units were by this date also known as cohortes palatinae. The old equites singulares Augusti still existed as the imperial horse guard, although these guardsmen had traded in their name for equites dominorum nostrorum. New guard units had been created in addition to the old. A mounted schola scutariorum was probably already part of the imperial guard. The unit of protectores consisted of promising men being groomed for higher commands. Elite legionary detachments like the Ioviani and Herculiani drawn from the legio I Iovia Scythica and legio II Herculia and the lancearii recruited among the legionary light infantry were permanently attached to the comitatusVexillationes of picked cavalrymen from the frontier units and elite auxilia were also included.

The frontier armies

The reign of Diocletian and his fellow emperors saw a massive increase in the number of legions. There were 39 legiones in existence in 286, but this number was almost doubled over the next thirty years. This did not however mean that the total strength of the army was increased on the same scale. Although the structure and establishment strength of these new formations were similar to that of earlier units, some of the tetrarchic legions were formed by combining existing units of the auxilia. These formations were distributed in pairs among the new, smaller provinces. Some new auxiliary units were also created, but the overall strength of the auxilia probably dropped as a result of the formation of legions from auxiliary cohorts.

Recruitment for the enlarged armies proved to be a problem. Not only were old conscription regulations applied with more severity than before, but several new measures were introduced to fill the ranks. Sons of serving soldiers and veterans were now by law required to enlist in the army. The protostasia, a recruitment tax on landownership, was a novel measure. Landowners were obliged to furnish army recruits in proportion to the size and yield of their properties. Those owning only small tracts of land were grouped together and taxed collectively. Not all parts of the empire were subject to levies of men. In the provinces whose population was considered to lack the required martial spirit, the recruiting tax was converted into payments of money known as the aurum tironicum or recruit gold. This money was used to provide bounties to attract volunteers. Men were also recruited from outside the empire, either voluntarily or by the incorporation of barbarian POW’s in the army.

The late Roman army

The field armies

The late Roman army contained several different field armies. Some of these, the so-called praesental armies, were under the direct control of the emperors and were the successors to the third century sacer comitatus. Other formations were based in the provinces and served as regional reaction forces. The field army units were composed of both palatini and comitatenses. There were few, if any, differences between these classes of troops, though the former carried more prestige. Cavalry units consisted of vexillationes palatinae and vexillationes comitatenses that provided a mix of heavy, medium and light cavalry. The legiones palatinaelegiones comitatenses and the auxilia palatina consisted mostly of heavy infantry, although some units were also employed as light infantry and archers. The legiones pseudocomitatenses attached to some field armies were detached formations from the frontier armies. A new development was the formation of separate legiones of ballistarii. These formations consisted of artillerymen operating light torsion guns and crossbows.

Unit organisations and establishment strengths for the late Roman army are difficult to reconstruct. Legionary detachments had evolved into separate units and were now termed legio rather than vexillatio. This meant that a legio could compromise any number between 500 and 5000 men. However 1000 to 1200 soldiers appears to have been a common establishment strength for many of the smaller legions. The internal organisation of these new legions is hard to establish. Although the ancient sources mention centuriaemanipuli and cohortes, the references appear formalistic and may not reflect actual conditions. The auxilia palatina consisted partly of newly raised units, but others had evolved from existing auxiliary cohortes. Their strength and organisation were probably similar to those of military cohorts. Cavalry vexillationes are likely to have been 500 strong with internal unit organisation similar to that of the earlier alae. A major break with the past army organisation was the removal of mounted troops previously attached to infantry formations. Units in the late Roman army consisted of either horsemen or foot soldiers, not a mix of both.

Command of the field armies was normally in the hands of senior officers known as magistri, though minor armies could be commanded by a comes. There were some minor variations in the titles of the field army commanders but there appears to have been little difference between the rank and function of a magister equitummagister peditum or magister militum. Command of units of any kind was by now generally in the hands of a tribunus. These tribunes were professional military officers who had often served as a protector at the imperial court. The tribuni vacantes were officers that were not directly attached to army formations and served in similar capacities as the earlier centuriones supernumerarii. The designation praepositus merely indicated the function of commander rather than an actual military rank. Centuriones were by this date more commonly referred to as ordinarii and centenarii. Officers with identical titles served in both cavalry and infantry units. Optiones received the new title of biarchus. Many other new designations for officers and NCO’s appear in the sources, but are often difficult to interpret.

Unit titles in the later Roman army were of a slightly different style than those of their early imperial counterparts. Although a lot of units retained names derived from unit numbers, like the Quarti Dalmatae, or their armament, as the Sagittarii Dominici did, there were a few peculiar late Roman practices. Many formations carried the designations of seniores, the ‘old ones’ or ‘veterans’, and iuniores, the ‘young ones’ or ‘recruits’. These titles were probably connected to a split-up of the armies among the sons of Constantine that resulted in small cadre forces being detached from existing units to form the backbone of newly recruited formations of the same name. As both types of unit received replacements in an identical fashion iuniores and seniores alike were soon composed of a similar mix of recruits and experienced men. Some late Roman army units also carried barbarian tribal names, but like the titles of earlier auxiliary units these were usually not representative of the ethnic origin of its soldiers, the majority being of Roman rather than foreign extraction.

The frontier armies

The frontier forces were entitled limitanei or riparii. These consisted of infantry legionescohortes and numeri and cavalry vexillationesalae and cunei. Frontier legiones were generally but not invariably larger formations than those found in the field armies with a strength and organisation resembling that of the earlier legions. Many units of the limitanei, both legionary and auxiliary, were divided over a number of small fortified bases. Often labelled a peasant militia with low fighting value in modern studies, these troops were in fact professional military units not significantly worse in calibre from those in the field armies. The palatini and comitatenses were regularly supplemented by forces drawn from the frontier armies.

Armour and equipment

Contrary to popular opinion late Roman troops were as heavily protected by armour as their early imperial predecessors. Although according to the available evidence the famous “lorica segmentata” was no longer in use after the late third century, literary and depictional sources indicate a continued general use of scale, mail and lamellar body armour by both mounted troops and foot soldiers. A padded leather and linen protective vest known as a thoracomachus was worn beneath metallic armour. Additional protection was provided by splinted greaves and armguards, notably in the ranks of the heavy cavalry. Helmet bowls were by this date usually constructed of several segments. The distinction made in some modern works between cavalry and infantry types does not appear to reflect ancient practice. Shields for all troop types were generally of oval or round shape. The unit shield patterns for many field army formations have been preserved in the Notitia Dignitatum, apparently with a remarkable degree of reliability.

Late Roman soldiers carried a variety of missile weapons. The introduction of new names for shafted weapons tends to disguise the fact that there was little essential difference between early and later imperial military practice. Heavy infantry continued to use javelins with long iron shanks similar to the earlier pilum. These could have both pyramidical points for better armour penetration or viciously barbed heads for use against unarmoured targets. Lighter javelins of different types remained the normal equipment of the cavalry, the light infantry and the rear ranks of infantry formations. There may however have been a greater emphasis on longer range fire power. A genuinely new addition to the armoury was the weighted throwing dart, the plumbata or martiobarbulus. This gave troops missile weapons with an improved range, though carrying the penalty of a somewhat decreased penetration power. Also the more widespread indications for the incorporation of archers in javelin armed units may point to an increase in the proportion of archers in late Roman formations.

The sword remained the weapon of choice for close quarter combat, though thrusting spears, daggers and axes were also employed. From the second century AD onwards weapons with longer blades had gradually replaced short swords in infantry service. The change in weapon type does not appear to have been linked to a drastic alteration in the tactics of the Roman heavy infantry. Troops continued to fight in close order formations using cut-and-thrust swordplay. Apart from the appearance of weapons and equipment little had changed from the days of the Roman republic.


The late Roman army is often stated to have suffered from barbarisation, a deterioration of old standards as the result of the recruitment of large numbers of barbarians, especially Germanic tribesmen, from across the borders of the empire. In fact the recruitment of barbarians into the ranks of the late Roman army did not take place in extraordinary numbers. Recent research indicated that even in the auxilia palatina, formerly considered to be heavily barbarian in composition, only a fifth to a quarter of soldiers were of barbarian extraction. Many early imperial army units contained a higher proportion of foreigners or only recently subjected barbarians. The majority of troops in the late Roman army were therefore of provincial Roman origin.

Barbarian influence on tactics, equipment and organisation also appears to have been very limited. The longer swords used by Roman infantry soldiers from the second century AD were not a sign of changing tactics. The use of the Roman short swords for stabbing rather than slashing has always been overemphasized in modern literature. Even the republican legionaries are explicitly described by Polybius to employ their Spanish swords for slashing as well as thrusting. The longer blades of late Roman troops were pointed and would have increased their reach in close quarter battle. The spatha was in fact not a weapon that Romans took over from Germanic barbarians, but a separate Roman development of earlier Celtic blades. As most weapons of this type found across the borders were imports from the Roman empire it appears that the barbarians adopted a Roman weapon rather than the other way round.

The performance in battle of late Roman troops was not significantly worse than that of their early imperial counterparts. The Roman army had never been an invincible war machine. The battle at Adrianople fitted in the list of Cannae, Carrhae, the Varian disaster, Tapae and countless other defeats. Even poorly armed Judean rebels destroyed the legio XII in the early stages of the Jewish War. The late Roman army had more than a fair chance of victory against any barbarian opponent it met. Persians, Sarmatians and Germans all alike were defeated time and again.

3. The Army of Republican Rome

It is hard to overestimate the importance of warfare in the Roman republic. Waging war was the most important way of acquiring the reputation and wealth that the Roman elite needed for a successful political career. Each year new men came forward to fill the annually elected magistracies, each intent on securing their political future by achieving military victories that would ensure them the high honour of a triumphus. Rome was therefore in this period almost continually at war and gradually extending its power across Italy and the Mediterranean world.

The legions

The Roman army of the middle republic was a militia army. It was composed of a number of legiones recruited among the citizen body which were levied for specific campaigns. Under normal circumstances four such legions were under arms which were assigned two apiece to the two consules. In case more units were needed these were placed under the command of praetores or pro-magistrates.

The legiones were numbered sequentially with the numbers I to IV being reserved for the units under the command of the consules. Contrary to imperial practice the numbers carried by the units were not duplicated. The shifting of the composition of the army over the years meant that from time to time existing units received a new numeral. As units were levied for specific campaigns and disbanded when no longer needed, units did not have the opportunity to develop a distinct identity. The honorary titles so familiar of the imperial legions only developed during the first century BC as legions were kept under arms for a prolonged time.


In republican Rome the right to serve in the army was a privilege of the assidui or propertied citizens. Together these formed the classis or populus. This restriction was imposed by the fact that the government generally did not take responsibility for the arming of its fighting men. Citizens were expected to equip themselves at their own cost with the necessary armour and weaponry when called up for service. Those not able to meet the property requirements for army service were known as the capite censi, the headcount, or as proletarii. These poorer citizens were only enrolled in times of emergency and equipped at state expense. Though the capite censi usually served as rowers in the navy they were at times incorporated in the legiones. Extreme measures were taken in the aftermath of Cannae with the formation of several units composed of volones, freed slave volunteers. Property qualifications for service in the army were gradually lowered as time went by to enlarge the potential pool of recruits. Generally the number of volunteers in the army was limited, though campaigns with lucrative prospects of plunder like those against Macedonia could attract larger quantities of men eager to serve.

Roman citizens that met the property qualifications were liable for conscription from the age of seventeen, though repeated legislation against the enlistment of younger soldiers indicates that recruits could be very young indeed. Up to the age of 46 citizens of means remained under the obligation to serve. The maximum number of years to be spent in the army was set at sixteen, though this limit was removed in time of emergency. Gradually however it became the norm to serve six years in succession before being discharged with reservist obligations. Cavalrymen on the other hand had to serve ten campaigns before being released.

The cavalry arm of the republican legion was constituted from wealthy citizens drawn mainly from the ordo equester able to meet the extra expense of providing a horse and its necessary equipment. Though a few select individuals served with a horse provided by the state, the so-called equus publicus, most cavalrymen bore the cost of their mounts themselves. The great financial burden of serving in the cavalry limited the size of the legionary horse. To some extent this lack of numbers was made up by the larger contingent of allied and auxiliary cavalry.

Pay at this date was minimal, barely meeting the expenses for equipment, food and other necessities. Soldiers in the republican army therefore needed other sources of income. With Roman armies almost continually campaigning abroad the opportunity for plunder was however great. This helped ensure a continued support for expansion of the empire.

Legionary armament

The Roman cavalrymen were armed in a similar way to their counterparts in the Hellenistic armies. Legionary horsemen were equipped with helmet, body armour, shield, sword and a thrusting spear. The majority of troopers served as shock cavalry, though there are indications that some men may have served as ferentarii, light cavalry skirmishers. Legionary light infantrymen were at times intermixed with the cavalry to bolster its strength.

The legionary infantry were divided in a number of classes with varying equipment and battlefield duties. The youngest and poorest soldiers served as light infantry which were known as veliteslevesrorarii or ferentarii. These light infantrymen were backed up by more heavily armed antesignani. The primary strength of the legio however resided in its heavy infantry. This was divided in three main divisions. The first of these were the hastati, the ‘spearmen’. These consisted of relatively young soldiers and were usually deployed in the first battle line. The second class were the principes or ‘leaders’. These men constituted the cream of the army and were normally deployed in the second battle line. The veteran triarii or pili made up the third class and were either deployed in the third battle line or left behind to guard the camp.

The legionary light infantrymen were mostly equipped with a parma or buckler, a number of hastae velitariae or light javelins, a sword and a helmet covered with an animal pelt. Some may however been armed with a sling. The antesignani used to support the light troops carried equipment similar to the heavy infantry with pila and body armour being mentioned in the sources. The hastatiprincipes and triarii were equipped with helmet, body armour, greaves, swords and large scuta or shields. Most men wore a copper alloy pectorale, though the wealthiest legionaries wore either scale or mail armour or an anatomical cuirass. The men of the first two battle lines carried heavy javelins called pila, but the usual shaft weapon of the triarii was a long stabbing spear. Double edged swords were the main weapon used in combat, the famous gladius Hispaniensis being derived from Spanish examples. Torsion gun artillery was at times used by the legions in this period, though it may not have been allocated on a regular basis.

The legion deployed usually in a formation of three battle lines of heavy infantry protected by a screen of skirmishers. The manipuli would initially deploy with the centuriae positioned one behind the other for ease of manoeuvre. Gaps were left between the manipuli but these were closed before engaging the enemy by the centuriae posteriores moving up to position themselves on the left of the centuriae priores. Tactics were generally simple consisting mainly of a blunt frontal attack. First the hastati would engage the enemy, throwing their pila before charging with their swords. These troops were relieved by the units of the principes in case of failure. The triarii were used as a last resort, the Latin expression ad triarios redisse being used to indicate that one was in a desperate position. Roman commanders confident in the ability of the hastati and principes to secure victory in battle left the triarii behind to guard the camp. Given the militia nature of the army at this point and the lack of prolonged and continuous training of the troops Roman tactics were by necessity predictable. Only when troops were kept under arms for years at a time could commanders like Scipio Africanus attempt to introduce more sophisticated tactics.

The organisation

The strength of a legio was variable and depended on the specific needs of a campaign. The authorised strength of foot varied between some 4200 to over 6000 infantrymen and the establishment strength of the horse varied between 200 and 300 troopers. In a legion of 4200 this was divided in some 1200 each of veliteshastati and principes and 600 triarii. An increase in the number of infantrymen did not affect the number of subunits as the strength of these was merely increased. It was also usual that when the legion’s complement was strengthened the units of triarii generally received fewer extra men than the other classes of troops.

legio was subdivided in thirty manipuli consisting of two centuriae. Command of the manipulus lay in the hands of the senior centurio commanding the unit on the right of the formation, the officer of the other centuria acting as his deputy. The hastatiprincipes and triarii each had ten such manipuli numbered I to X. The other infantrymen were attached to these units having no separate organisation. The strength of the units of triarii was generally only half that of the hastati and principes Gradually new subdivisions called cohortes were introduced in the Roman legiones, probably patterned on similar formations of the Italic allies. In these units one manipulus of hastatiprincipes and triarii with their attached light infantrymen were brigaded together. The need for small independent units to fight against the tribesmen in the mountains of Spain is likely to have been the stimulus for the creation of these new legionary subdivisions.

Each legio had its own organic cavalry arm. The usual strength of the legionary horse varied between 200 and 300 cavalrymen. These horsemen were organised in decuriae of each ten troopers under the command of a decurio, three decuriae being grouped together in a turma under the overall command of the senior decurio. Within each decuria a rear rank officer was appointed by its commander.

The officers

The command of a legio was entrusted to six tribuni militum drawn from the senatorial class. A minimum of five to ten years prior army service was required before men were eligible for the post of tribunus militum. Former praetores and consules as well as young men at the start of their public careers served as tribunus ensuring that at least part of these officers were experienced commanders. Part of the tribuni were elected by the popular assembly and known as comitiati while other officers of this rank termed Rufuli were selected by the commanders-in-chief. Junior officers known as centuriones were selected by the tribuni among the more experienced fighting men. Commanding the manipuli were the centurions called hastatus priorprincips prior and pilus prior with the hastatus posteriorprinceps posterior and pilus posterior personally selected by the former acting as their deputies. Great prestige was attached to the post of primus pilus, the senior centurion commanding the first manipulus of triarii. As senior centurion of the legion this officer was admitted to the councils of the high command.

The centuriones were assisted in their tasks by a small number of NCO’s. The republican legionary organisation was however much simpler than the elaborate imperial system of principales and immunes. An optio served as a rear rank officer keeping the legionaries in check, a signifer carried the unit’s standard and a tesserarius was in charge of the watchword. Attached to each manipulus as military musicians were further a cornicen and tubicen. Contrary to imperial practice the NCO’s probably earned the same pay as the ordinary soldiers, centurions themselves at this time only being paid twice the amount of the rank and file.

The fleet

The military power of the Roman state had until the Punic Wars been mainly based on land. The struggle with Carthago forced the Romans however to become a maritime power as well. During the First Punic War a large fleet was built from scratch allegedly using a stranded Carthaginian vessel as a prototype. The standard type of warship was the quinqueremis with five rowers on three banks. The lack of skill of the Roman sailors meant that the traditional manner of naval combat with manoeuvring galleys trying to ram their opponents was abandoned for a new approach. Roman vessels were equipped with a corvus or raven, a movable boarding bridge which enabled the Romans to turn naval battles in engagements between marines rather than ships. This new invention enabled the Romans to score some spectacular successes against the Carthaginian fleet, but the added weight of the boarding bridge made their vessels less seaworthy resulting in heavy losses due to storms.

The achievement of military superiority on sea during the Punic Wars enabled the Romans to land their land forces on the coast of North Africa to bring the war to their enemy. The naval supremacy gained by the Roman fleet also resulted in Carthago, formerly relying on its sea power, choosing to fight the Second Punic War on land instead. With the demise of Carthago as a leading naval threat the Romans lost interest in maintaining a powerful fleet themselves. With the seas no longer patrolled by warships this led to an increase in piracy in the Mediterranean.

The allies

The citizen troops serving in the legiones were supplemented by troops drawn from allied and conquered communities, the socii. Another term in general use for the socii was auxilia, supporting troops, or cohortes alariae. These forces were divided in several types but the most important were the Italic socii or allies. Among these the socii nominis Latinis, the allies of the Latin league, were the most prominent. Generally the majority of these Italic allies were staunchly loyal to the Roman cause. Even after the series of disastrous defeats inflicted by Hannibal only a minority of Italic communities defected to the enemy. The Italic socii were occasionally rewarded for their services by the granting of Latin rights or Roman citizenship. The increasing rarity of these grants in the second century BC was one of the main causes of the Social War fought between Rome and her Italic allies.

The Italic allies were organised in alae sociorum, one of which was attached to each Roman legion. The name of ala or wing was derived from their usual position on the flanks of the citizen troops. As with the legions the establishment strength of these units was variable and adjusted to the requirements of the envisaged campaigns. Few allied communities were large enough to supply a full sized ala sociorum and therefore these units were usually composed of a number of contingents supplied by various allies. These contingents were organised in cohortes with a praetor drawn from the upper class in command. The allied praetores were however subordinated to Roman praefecti sociorum within the organisation of the alae.

The exact structure of the allied alae is somewhat unclear. However most modern authorities assume that the units of the socii were generally similar in composition to the citizen troops with a mix of both light and heavy infantrymen and cavalrymen drawn from the same community. However some passages in the sources mention allied contingents consisting solely of skirmishers. This may indicate that there was no generalised pattern and the type as well as number of forces supplied varied for each ally. A major difference between the legions and the alae sociorum was in the number of horsemen attached. Generally the allied formations counted double or triple the number of cavalry attached to the citizen units.

Among the Italic allies one fifth of the infantry and a third part of the horse were selected for service as pedites – and equites extraordinarii. This elite corps served as a bodyguard to the Roman generals and formed the vanguard on the march. These troops were organised in their own cohortes. If later imperial practice is a reliable guide, soldiers were individually picked for service in these guard formations. As a citizen counterpart to the allied extraordinarii some Roman commanders formed a cohors praetoria of picked legionary troops.

In addition to the ground forces supplied by the Italic allies, the so-called socii navales, the naval allies, were responsible for furnishing Rome with ships and crews. After the Punic Wars Rome increasingly relied on such allies to supply the vessels and men whenever the formation of a fleet was required. The warships provided by the allies were of the current types such as triremes and quinqueremes.

Next to the Italic allies existed other supplementary forces. Some of these were true allies bound by treaty obligations while others served as mercenaries. The numbers and type of these forces varied as much as their origin. Many were employed only in local campaigns, but Numidian light cavalry, Balearic slingers, Cretan archers, Gallic and Thracian horsemen regularly served in Roman armies far from their home countries. To some extent these troops provided complementary fighting skills to those of the Roman legions and their Italic allies.

4. The Roman army of the late republic

The army of the late republic

The Roman army of the late republic is often connected to the so-called Marian army reforms. In fact radical reforms of the army structure were few. What novel measures were taken, were moreover in fact the work of other generals than Gaius Marius. One of the more current misconceptions regarding the Roman army in the later republican era concerns the introduction of a professional army recruited from volunteers to replace the militia army composed of conscripts. Conscription was not ended by the fact that Marius accepted volunteers from the capite censi. Draftees rather than volunteers continued to provide the bulk of legionary recruits. Neither is there much actual evidence for wide ranging organisational and tactical reforms by the great general. The cohors appears to have been incorporated in the regular organisation well before the days of Marius. Although gladiatorial trainers were employed as an emergency measure by Rutilius Rufus after the defeats inflicted on the Romans by the Cimbri and Teutones there are no indications available that this entailed a drastic improvement in training standards. It is also very doubtful that instructors of this unsuitable background continued to be employed after the emergency situation had passed. The light infantry velites were not abolished by Marius, merely being equipped with different shields and continuing to serve in the wars of Sulla against Mithridates. One measure however is very closely associated with Marius. This general reduced the size of the legion’s baggage train by requiring his soldiers to carry much of their equipment themselves. This resulted in the heavily laden legionaries being nicknamed muli Mariani or Marius’s mules.

The command structure of the Roman army underwent considerable changes in the late republic. The role of the consules as the primary commanders of Rome’s legions diminished, finally being ended by the Sullan reforms of the constitution. In their stead proconsuls and commanders granted extraordinary powers were now the most important army leaders. The restriction on the maximum number of legions under the command of a single general was lifted. Armies could now be made up of up to several dozens of legions. The nature of the army also changed with soldiers being loyal to their commanders rather than the Roman state itself. The fact that campaigns in this period tended to be more prolonged and the securing of discharge benefits by the personal influence of the generals attached the soldiers much more closely to their leaders.

The legions

The legiones provided the citizen troops of the Roman army. As a result of the expansion of the empire the number of units under arms at any given moment had risen since the middle republic. Some of these units remained in service for longer periods, discharging soldiers who had served their time and accepting new recruits in their place. These semi-permanent units began gradually to develop their own distinctive identity, a process accelerated by the prolonged Gallic campaigns of Caesar and the civil wars that followed it. With different parties in the civil wars each levying their own armies, legionary numerals started to be duplicated. Legions started to adopt honorary cognomina and acquire particular symbols and signs. Some commanders valued this esprit de corps of their legiones to such an extent that they preferred to levy new units rather than dilute their veteran formations with the influx of new men.

Legionary recruitment

Contrary to popular opinion the majority of legionary soldiers in this period remained levied conscripts rather than volunteers drawn from the capite censi. The property qualifications that had already been lowered several times in the previous decades however appear to have been waived altogether. To enlarge the legionary strength legiones vernaculae were raised from provincials rather than Roman citizens on several occasions, notably during the civil wars of the first century BC.

Men enlisted in the army now generally had to serve for longer periods of time and were often from an impoverished agrarian background. Roman generals interested in gaining the loyalty of the troops were therefore keen on securing special discharge benefits for their men. This often took the form of distribution of land to time served soldiers. For this purpose land was on several occasions confiscated on a huge scale, both in Italy as well as the provinces.

Service conditions were greatly improved during the civil wars. Previously pay had barely covered expenses and soldiers gained only by the opportunities for plunder. The fighting between the various civil war parties enabled the loyalty of the troops to be converted in wealth. Commanders anxious to attach the legionaries to their cause distributed generous bounties known as donativa to their troops on a regular basis. Caesar did much to enlarge his popularity by doubling the standard rate of pay and providing silvered and gilded equipment to his men. The provision of weaponry and equipment by the Roman government and commanders to the troops remained an exception to the rule, the soldiers still being expected to equip themselves at their own expense.

Legionary organisation

The composition of the legio in the late republic was different from the earlier formations. The light infantry velites disappear from the records after the battles of Sulla in Asia Minor, their role being taken over by a mix of legionary antesignani and auxiliary skirmishers. The units of the triarii were by now brought up to the same strength as those of the hastati and principes and by this date carried the pilum in place of the thrusting spear. Ten cohortes combining manipuli of hastatiprincipes and pili with the same number had become part of the regular legionary organisation. The battle formation of the legion also changed. The triple battle lines of ten manipuli had either been replaced or supplemented by a new formation with four cohortes in the first and three cohortes each in the other two battle lines. This new deployment meant that the legion now had twelve rather than ten manipuli available for action in the front line.

The old legionary cavalry recruited from the equites Romani disappeared from the legionary organisation at some point in the first century BC. This may have left the legio without an integral cavalry arm. However if speculatores in this period were mounted troops as their imperial counterparts certainly were, a very small number of legionaries may have been cavalrymen. The apparent lack of substantial citizen cavalry was made good by recruiting large numbers of barbarian and provincial horsemen. The Bellum Gallicum relates of one interesting occasion when Caesar had the entire legio X mounted on horses from the auxiliary troopers to serve as a reliable cavalry guard during a meeting with the German chieftain Ariovistus.

In the civil wars commanders spent much effort in the formation of loyal elite units. This was partly achieved by employing foreign bodyguards from barbarians with a high reputation for loyalty and devotion to duty. Hispanic, Gallic and German horsemen served widely as personal guards. However picked citizen troops also played an important role. Caesar established the legio X Equestris as his favourite unit while other commanders selected legionary soldiers for service in cohortes praetoriae or bodies of speculatores. The antesignani were another elite corps picked from the bravest legionaries and employed in a variety of roles including light infantry skirmishing as well as spearheading assaults.

Legionary officers

There were some changes in the structure of the legionary officer corps compared to the legions of the middle republic. The status and remuneration of the centuriones in the Roman army was significantly raised in the late republican period. This was in recognition of their importance to the army. The pay raise for the centurions may well have been accompanied by an increase in pay to the non-commissioned officers which would eventually emerge as the principales of the imperial army. Legionary tribuni which had previously included men of great experience, were by this date often young and lacking in experience. This resulted in the command of legiones being given to legati appointed by the army commander rather than to the senior tribunus. These legati had however not yet developed in the similarly named legionary commanders of the imperial army as they were not attached to particular units and regularly shifted commands.

The auxilia

After the Social War waged against the Italic allies Roman citizenship was granted to all of these below the river Po. This meant that Italic soldiers were now directly recruited in the legiones rather than serving in separate alae sociorum. Auxiliary forces from outside Italy were however employed on a large scale. Many of these forces were raised for specific campaigns and disbanded as soon as their services were no longer needed. Only a minority of these units, notably cavalry, achieved a semi-permanent status.

Part of the auxiliary forces levied for service in the Roman army were organised on the Roman pattern in cohortes and alae of some 500 men. Command of these units was partially entrusted to nobles from the communities that supplied the troops, though legionary centuriones and equestrian officers were also employed. Equipment and tactics of the auxiliaries were for a large part those of their native regions. Some units however were equipped and trained according to Roman standards. A peculiar feature was the formation of some cavalry formations as more or less private armies of retainers by Roman officers, the ala Scaevae being an example.

Little is known of the remuneration and other service conditions of the auxiliary forces. During earlier times allies received upkeep from the Roman state but no regular pay was provided. Other troops though are described as mercenaries in the sources indicating that at least some auxilia were paid for their services. To a limited extent auxiliary soldiers with good service records were granted Roman citizenship. However these grants were made to individuals and were not a regular occurrence. Only after the reign of the emperor Claudius would time served soldiers in the auxilia receive citizenship on a regular basis.

Special thanks to Sander van Dorst, who is the author of this text.

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