Ancient History & Civilisation

The Army of the Principate

The legions

By the death of Rome’s first Emperor, Augustus, in ad 14 the Roman army had become a fully professional and permanent institution. The heart of the army remained the legions, many of which would endure for centuries, vanishing only when destroyed in action or, more rarely, disbanded in disgrace. Augustus had inherited a force of over 60 legions by the end of the civil wars, but reduced this to 28. This total was only to fluctuate a little above or below 30 for the next 300 years. Each legion was given a number and most rapidly acquired names and titles as well. The system was never entirely logical, suggesting that there was strong resistance from some existing legions to give up their identity. As a result several numbers were duplicated and there were no fewer than three third legions. The situation became even more apparently confusing as later emperors raised new legions in sequences starting at ‘one’. Under Augustus the highest-numbered legion was XXII Deiotariana. This had an unusual origin, since it was formed from the army of the Galatian King Deiotarus, who had equipped, organized and trained his soldiers on the Roman model. The original recruits appear to have been given Roman citizenship, but soon the legion was recruited from men who already possessed the franchise and treated in exactly the same way as all the other legions. Other unit titles preserved some trace of their origins. Three legions, X, XIII and XIV, were known as Gemina or ‘Twin’, suggesting that they were originally formed by the amalgamation of two units.

Some legions had developed a distinct identity and reputation in the post-Marian army, but the Augustan reforms institutionalized this trend. Their names sometimes expressed martial virtues, such as Ferrata (Ironsides) or Fulminata (Thunderer), or commemorated regions where the unit had presumably served with distinction. Traditions were now passed within a legion from one generation of soldiers to the next. Legionaries were proud of their unit and contemptuous of others. The standards and the symbols on men’s shields, as well quite possibly as other peculiarities of dress and routine, made each legion unique. Even on short inscriptions, and especially on important ones such as epitaphs, legionaries usually mention their legion. Emperors carefully granted the right to titles to win the favour of their soldiers. Therefore after their prominent role in the defeat of Boudicca in AD 60, Nero added the names Martia Victrix (Mar’s own, the Victorious) to the full title of Legio XIV Gemina. Trajan, whose full name was Marcus Ulpius Traianus, named Legion XXX Ulpia Victrix. Not all honours were won in war, Claudius granting the title Claudia pia fidelis (Claudius’ own, pious and faithful) to Legio VII Macedonica and Legio XI when they refused to follow their commander in an attempted coup.

Roman soldiers had a sum annually deducted from their pay to provide for the costs of funeral ceremonies. However, this charge does not seem to have covered anything more than the most rudimentary of markers for the grave, and many individuals set additional money aside to pay for more substantial memorials. Even a simple, unadorned inscription like this would have represented a sizeable investment.

There had been no set term of service even after the Marian reforms, although the traditional maximum of 16 campaigns or years may have continued to apply. Legions sometimes served for the duration of a conflict, but many remained in garrison at a war’s end. Augustus established the length of service in his new, permanent legions as 16 years with a further four as a veteran. Veterans remained with their legion, but were excused guard duty and fatigues and in theory only obliged to fight in defence of the legion’s base or camp. However, a shortage of recruits resulted, later in Augustus’ reign, in the extension of service to 20 years with an additional five as a veteran. Although the change was at first bitterly resented, it remained standard throughout the Principate.

Under Augustus the command structure of the legion was laid out more clearly and a permanent commander appointed. This was the legatus legionis, a senator, usually in his early 30s. The second-in-command was the only other senator in the unit, the tribunus laticlavius, a man usually in his late teens or early 20s and with little or no prior military experience. Third-in-command was the praefectus castrorum, or Camp Prefect, who was an experienced former chief centurion and had probably spent most of his adult life in the army. The Prefect seems to have been responsible for many aspects of administration which required some technical knowledge. There were also five tribunes recruited from the equestrian order, tribuni angusticlavii, who performed whatever tasks were allocated to them but commanded no specific section of the legion. Beneath these were the centurions, six to each cohort, whose titles preserved the traditions of the old manipular legion. In ascending order of seniority these were called hastatus posterior, hastatus prior, princeps posterior, princeps prior, pilus posterior and pilus prior. Pilus was an alternative name for triarius.

Legions of the Principate

Legion

Formed

Destroyed/disbanded

Notes

I Germanica

Late Republic

dis. ad 70

Disbanded after Civilis’ revolt

I Adiatrix pia fidelis

Nero

 

Originally formed from men drafted from the fleet

I Italica

Nero

 

Raised in Italy. All the original recruits are supposed to have been 1.8 m (6 ft) tall Short-lived, civil war legion

I Macriana

Nero

dis. ad 69-70

I Flavia Minervia pia fidelis

Domitian

 

Titles awarded for loyalty to Domitian

I Parthica

Severus

 

Raised for his Parthian expedition

II Augusta

Late Republic/ Augustus

 

Probably originally called Gallica

II Adiatrix pia fidelis

Nero

 

Originally formed from men drafted from the fleet

II Italica

M. Aurelius

 

Probably formed in ad 165

II Parthica

Severus

 

Raised for his Parthian expedition

II Traiana fortis

Trajan

 

‘Strong’, probably awarded for service in Dacia

III Augusta pia fidelis

Late Republic/ Augustus

   

ID Cyrenaica

Late Republic

 

III Gallica

Caesar

 

III Italica concors

M. Aurelius

 

‘United’, probably formed in ad 165

III Parthica

Severus

 

Raised for his Parthian expedition

ПП Macedonica

Caesar

dis. ad 70

Disbanded for defection to Civilis

IIII Flavia felix

Vespasian

 

‘Lucky’, formed from the legions disbanded in AD 70

НП Scythica

M. Antony?

   

V Alaudae

Caesar

dstr. under Domitian?

The ‘Larks’, originally raised in Transalpine Gaul

V Macedonica

Late Republic

   

VI Ferrata fidelis constans

Caesar

 

The ‘Ironsides’, faithful and constant

VIVictrix

Late Republic

 

‘Victorious’

VII Claudia pia fidelis

Caesar

 

Given titles for remaining loyal to Claudius in AD 42

VII Gemina

Galba

 

‘Twin’ - probably reformed from two legions c. ad 70

VIII Augusta

Late Republic

   

IX (or VIIII) Hispana

Late Republic

dstr. under Hadrian?

Possibly destroyed during the Bar Kochba rebellion in Judaea

X Fretensis

Late Republic

 

Fretensis was the strait between Italy and Sicily

X Gemina

Caesar

 

‘Twin’, formed from amalgamation of two units

XI Claudia pia fidelis

Late Republic

 

Given titles for remaining loyal to Claudius in AD 42

ХП Fulminata

Caesar

 

The ‘lightening-thrower’

XIII Gemina pia fidelis

Late Republic

 

‘Twin’, formed from amalgamation of two units

XIV Gemina Martia Victrix

Late Republic

 

Another ‘twin’. Other titles awarded for supressing Boudicca’s revolt in AD 60-61

Augustus claimed a special relationship with the god Apollo

XV Apollinaris

Augustus

 

XV Primigenia

Caligula

dis. AD 70

Disbanded for defection to Civilis

XVI Gallica

Augustan

dis. AD 70

Disbanded for defection to Civilis

XVI Flavia Firma

Vespasian

 

Reformed as new unit from XVI Gallica

XVII

Augustus

dstr. ad 9

Destroyed in Germany

XVIII (or XIIX)

Augustus

dstr. AD 9

Destroyed in Germany

XIX

Augustus

dstr. ad 9

Destroyed in Germany

XX Valeria Victrix

Augustus

 

Probably awarded titles for suppressing the Boudiccan revolt in AD 60-61

‘Grasping’, i.e. greedy for victory

XXI Rapax

Augustus

dstr. under Domitian?

XXII Deiotariana

Augustus

dstr. under Hadrian?

Formed from the army of the Galatian King Deiotarus

XXII Primigenia pia fidelis

Caligula

   

XXX Ulpia Victrix

Trajan

 

Raised for the Dacian Wars, during which it won the title ‘victorious’

A legion possessed a small cavalry force of some 120 men, but its main fighting strength remained the 10 cohorts. Each consisted on paper of 480 men, divided into six centuries each commanded by a centurion. There were 80 men in a century, divided into ten sections of contubernia of eight men. The contubernium shared a tent on campaign, and a pair of rooms in a barrack block, living and eating together. Such conditions tended to foster a very close bond between its members, of the type observable in the small units of modern armies. Contubernalis developed as a word for close comrade and was used by officers and men alike. To assist the centurion in running the century he had the same group of subordinate officers (principales) as the old Republican army, the optio, signifer, and tesserarius.

The Defeat of Boudicca

AD 60

In ad 43 the Emperor Claudius invaded Britain. The most serious rebellion the Romans were ever to face in the island came almost a generation later in AD 60.

It was led by Boudicca, widow of King Prasutagus of the Iceni tribe (who lived in the area of modern-day Norfolk) and was prompted by the brutal behaviour of certain Roman officials. The Queen rallied many supporters from her own and neighbouring tribes, sacked Camulodunum (Colchester), Verulamium (St Albans) and Londinium (London), and defeated a vexillation of Legio IX Hispana. When the revolt erupted the governor of the province, Caius Suetonius Paulinus, was campaigning in north Wales. He hastily returned and confronted the rebels at an unknown location.

The forces

1 The Romans: most of Legio XIV Gemina and part of Legio XX, supported by auxiliary infantry and cavalry. In total around 10,000 men commanded by the legate Suetonius Paulinus.

2 The Britons: there are no reliable statistics for the British army, but it was evidently several times larger than the Roman force.

Aware that he was heavily outnumbered, but that his men were far superior in training, equipment and discipline, Suetonius Paulinus deployed his army in a defile, with his flanks and rear protected by high ground and woodland. The legions were in the centre, the auxiliary cohorts on either side and the cavalry on the wings. Boudicca relied on her army’s size rather than any subtle tactics to crush the enemy. Behind the massed warriors was a line of wagons, from which the men’s wives watched the fighting. The Romans waited for the Britons to advance, but counterattacked when they were very close. After heavy fighting the Britons were routed with great loss.

Casualties

1 Roman: around 400 killed and somewhat more wounded (c. 8-10 per cent).

2 Britons: one source claims as many as 80,000 were killed, and certainly their losses were very heavy.

Results

The rebellion was decisively defeated although further operations were required to stamp out its last embers. Boudicca is believed to have despaired and taken poison.

A heavily romanticized 19th-century statue of Boudicca riding in her scythed chariot.

BOUDICCA (died c. ad 60-61)

Boudicca was wife of King Prasutagus of the Iceni, who had made his peace with the Romans soon after the Emperor Claudius invaded Britain in AD 43. British tribes often had more than one king at a time and it is probable that Prasutagus ruled only one section or clan of the Iceni. Boudicca’s name was probably derived from Bouda, a Celtic goddess of victory. When Prasutagus died in ad 60 bequeathing his possessions jointly to his daughters and the Emperor Nero, the Roman Procurator Decianus Catus (an official in charge of provincial finances) plundered his kingdom. His men flogged Boudicca and raped her daughters, outrages which immediately prompted rebellion.

The historian Dio Cassius, writing a century and a half later, described Boudicca as very tall, with long red hair, piercing eyes and a harsh voice - a picture which may owe more to the stereotype of the northern barbarian than the Queen’s actual appearance. He also says that she habitually wore a many coloured dress (probably tartan or checked), a golden torque around her neck, and a long cloak pinned in place with a brooch.

The first cohort appears to have been different. At the very least by the later 1st century ad, some, and perhaps all, legions had a first cohort broken into five instead of six centuries. Each century was double the normal strength at 160 men, so that the entire cohort mustered 800. In ascending order of seniority, its centurions were known as hastatus posterior, hastatus, princeps posterior,princeps, and primus pilus. All of these ranks, and especially the primus pilus, enjoyed immense prestige, their holders living in substantial houses rather than barrack rooms in a permanent camp. In the Late Roman manual of Vegetius, the author claims that the men of the first cohort were supposed to be taller than the men of the rest of the legion. A modern suggestion is that the cohort included the legion’s veterans. Either way, this might suggest that the first cohort provided a strong, elite force within the legion. Yet the evidence is by no means good enough to tell us whether all legions were reorganized in this way or only some. One possibility is that for reasons of prestige, or perhaps the scale of the local military problem, certain legions were selected to be enlarged in this way.

Legionaries in the Teutoburg Wald, ad 9

At the end of the 1st century вс the Emperor Augustus’ commanders undertook the conquest of a new province of Germany, covering the area between the Rhine and the Elbe. However, in AD 9 a major rebellion was led by Arminius, a chieftain of the Cherusci tribe. Feigning loyalty to Rome until the last minute, he led the provinrial legate, Publius Quinctilius Varus, into an ambush. The Roman army - consisting of Legiones XVII, XIIX and XIX, supported by three cavalry alae and six infantry cohorts of auxiliaries - was lured into the woods and marshes of the Teutoburg Wald where it was destroyed in several days of bitter fighting. Varus committed suicide before the end and only a handful of his men managed to escape. The loss of a tenth of the entire Roman army proved a terrible blow to the ageing Augustus, who is said to have wandered around his palace banging his head against the walls and shouting out ‘Quinctilius Varus, give me back my legions!’ Although other Roman armies were sent against Arminius and inflicted some reverses upon him, they proved unable to recover the lost province.

The professional auxilia

The Romans had always relied heavily on allied soldiers to supplement their armies. These were known generally as the auxilia, since they aided and supported the citizen legions. In the Mid Republic each legion was supported by an ala, and many armies also included contingents of non-Italian allies, often fighting in their native style. Usually these men were drawn from the theatre of operations in which the campaign was being waged. During the Punic Wars Roman armies in Sicily were supplemented by troops from the Greek cities of the region, those in northern Italy received aid from the local Gallic tribes, the forces in Spain usually included large numbers of Iberian and Celtiberian tribesmen, and the final defeat of Hannibal in North Africa owed much to Rome’s Numidian allies. Local allies were a useful source of additional numbers, but were often even more important in providing soldiers whose fighting styles were particularly suited to the conditions of the region. However, such allies were not always reliable, and a major disaster occurred in Spain in 212 BC when a Roman army was abandoned by its Celtiberian allies and then overwhelmed by numerically superior Carthaginian forces.

A 1st-century ad relief from the headquarters of the legionary fortress at Mainz showing an auxiliary infantryman. He brandishes a javelin in his right hand and has two more held behind his flat oval shield.

After the Social War the Italian allies (or socii) were absorbed into the legions, reducing the proportion of non-citizen soldiers in most Roman field armies. However, the practice of employing contingents from outside Italy continued and in many ways became more important. The post-Marian legions lacked integral cavalry and light infantry, so it was necessary for commanders to find such troops from other sources. During the campaigns in Gaul, Julius Caesar supported his legions with Gallic, German and Spanish cavalry, and Numidian, Cretan and German skirmishers. One of the reasons for the disaster at Carrhae in 53 вс was that Crassus lacked sufficient horsemen and missile-armed foot to combat the Parthian horse archers and cataphracts. Very little is known of the allies of this period, so that we cannot tell to what extent these were trained and disciplined. At least some of these units remained essentially the personal followings of a tribal war-leader, fighting for him in the same way that they would have done in inter-tribal warfare.

Known Auxiliary Regiments

Unit name

Additional titles

Formed

Served

Ala I Brittonum

Veterana civium Romanorum equitata

Domitian?

Pannonia Inferior, Syria?

Cohors I Septimia Belgarum

 

late 1st century?

Dalmatia, Germania Inferior*

Cohors 1 Britannica

Milliaria equitata civium Romanorum

Claudius? Or Domitian

Pannonia, Upper Moesia, Dacia

Cohors I Brittonum

Milliaria Ulpia Torquata Pia Fidelis

   
 

civium Romanorum

Vespasian?

Noricum, Pannonia, Moesia, Dacia

Cohors II Britannorum

Milliaria civium Romanorum Pia Fidelis

?

Germania Inferior, Moesia, Dacia

Cohors II Flavia Brittonum

equitata

Flavians

Moesia Inferior

Cohors II Augusta Nervia Pacensis

Milliaria Brittonum

Trajan

Pannonia, Dacia

Cohors III Britannorum

 

Flavian?

Raetia

Cohors III Brittonum

Veterana equitata

Flavian?

Moesia Superior

Cohors VI Brittonum

equitata Pia Fidelis

 

Cappadocia?

* A British origin for this unit has been suggested, but cannot be proven.

(Above) The tombstone of Genialis, an imaginifer (bearer of the image of the emperor - probably Claudius in this case) in Cohors VII Raetorum. The animal skin draped over his left shoulder was probably usually wont over his helmet. He died at the age of 35. having served in the army for 13 years.

(Above) An entire quingeniary ala of cavalry beginning to deploy. There are 16 turmae of 30 men, each led by a standard-bearer. At the front of the entire formation is the prefect and the ala’s standard. It is unlikely that a unit would actually tight in such a deep formation.

Under Augustus and his immediate successors, the auxilia were turned into a much more regular and professional force. Significantly they were not organized into formations of equivalent size to the legions or old Italian alae, but into units of roughly cohort strength. One reason for this was that it was far easier to shift such small units around the Empire as the situation required. Perhaps as importantly, the higher level of the legionary command structure gave the citizen soldiers a marked advantage in pitched battles should the foreign auxiliaries ever rebel.

There were three types of auxiliary unit - infantry, cavalry and mixed. The infantry were organized into cohorts, either quingenary (500 strong) or milliary (1,000 strong). In spite of their names, a quingenary cohort normally consisted of 480 men divided into six centuries of 80, whilst a milliary cohort mustered 800 men divided into 10 centuries of 80. The cavalry were also organized into quingeniary and milliary units, although in this case these were known as alae rather than cohorts. A quingenary ala consisted of 512 men divided into 16 troops (turmae) of 32 men. A milliary ala fielded a formidable total of 768 men in 32 turmae. The organization of the mixed units, or cohortes equitatae, is far less certain, but the most probable interpretation is that these had the same number of infantrymen as an ordinary cohort and added 120 cavalry and 240 cavalry for a quingeniary and milliary unit respectively. These cavalrymen were not as well mounted or equipped as the men in the specialist cavalry alae.

The auxilia provided the imperial army with the vast majority of its cavalry. It also provided men armed with longer-ranged missile weapons than the pilum, including units of foot and horse archers. There were also slingers amongst the auxilia, although as yet we know of no unit exclusively armed with this weapon, and it is possible that small contingents were included in other units. Our literary sources state that some cohorts were lightly armed, although none is specifically attested epigraphically. Most auxiliary infantry were close- order troops who fought in a manner very similar to the legions. They ‘supported’ the legions more by providing them with extra manpower rather than novel methods of fighting. The smaller units of the auxilia were especially useful in providing a cheaper and more flexible force for frontier policing.

A metope from the early 2nd- century AD Tropaeum Traiani at Adamklissi in Romania showing three auxiliary infantrymen. All wear mail, carry oval shields and have swords in their right hands.

Troops stationed in Italy

It was not until the very end of the 2nd century AD that a legion was permanently stationed within Italy itself. Augustus and his successors had not wished their reliance on military support to be too blatant. Nevertheless some troops were required by the emperor in Rome and Italy, and this led to the formation of the praetorian and urban cohorts.

Many Roman commanders had maintained a bodyguard unit known as the praetorian cohort after the headquarters (praetorium) in a camp. Augustus maintained such a force even after the end of the civil wars. Its size was kept at nine cohorts of 480 men, just smaller than a legion. At first only three cohorts did duty in Rome at any one time, but under Tiberius all nine cohorts were concentrated in the newly built barracks (the castra praetoria) on the edge of the city. Later emperors would also increase the size of each cohort to milliary strength. Each cohort was commanded by a tribune and the entire praetorian guard by two prefects. All of these officers were members of the equestrian order.

The praetorian guard gave the emperor the capacity to enforce his will on the population of Rome. They soon acquired a grim reputation for the arrest and execution of Roman noblemen suspected of plotting against the emperor. The support of the guard could make or break an emperor. Claudius was discovered hiding behind a curtain after the assassination of Caligula by the praetorians, who forced a reluctant Senate to grant him the throne. Nero’s position only became hopeless when the guardsmen abandoned his cause. In AD 193 the power of the praetorians was even more blatantly demonstrated. Having murdered the Emperor Pertinax, the praetorian prefect auctioned off the throne to the highest bidder from the walls of the castra praetoria.

The praetorians were expected to accompany the emperor to war. This was rare in the 1st century, but became increasingly common later. As a military force the praetorians were trained and equipped as legionaries, although some of their gear was considerably more ornate. We hear of praetorian cohorts being allowed to load their heavily decorated standards onto pack animals when their bearers had difficulty carrying them on a long march.

Attached to the praetorian guard was a cavalry force which steadily grew in size, which along with the emperors horse guards (equites singulars Augusti) reached a peak of 2,000 men at the end of the 2nd century ad. These men were specially chosen from the auxiliary cavalry and trained to a very high standard. There were also two paramilitary forces in Rome. The three (later five) urban cohorts acted as a police force, as well as providing one unit to guard the imperial mint at Lugdunum (Lyons) in Gaul. There were also seven cohorts of vigiles, who acted as a fire brigade and night police force in Rome itself. Both groups only ever took the field at times of extreme crisis, usually provoked by civil war.

A close-up view of praetorians on a relief found in Rome and probably dating to the early 2nd century вс These men have thick crests in long crest-boxes fitted to the top of their classical helmets.

A group of soldiers - who may well be praetorians - on Trajan's Column. These men have somewhat smaller crests than those shown above.

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