The Roman Army

Ancient Rome

The Roman Army

Gary Edward Forsythe: Assistant Professor of Classical Languages and Literatures, University of Chicago. Author of The Historian L. Calpurnius Piso Frugi and the Roman Annalistic Tradition. Robert A. Guisepi: Author of Ancient Voices

(Re-printed by permission)

"Remember, Roman, that it is for thee to rule the nations. This shall be thy task, to impose the ways of peace, to spare the vanquished, and to tame the proud by war."

Portion of this Information Contributed by Sander van Dorst

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The history of Rome is in many ways, the history of its highly successful armies. Between the 2nd century BC and the 1st century AD Rome expanded from a city-state to an empire controlling the whole Mediterranean basin. This achievement was the work of its legions

The earliest Roman army formation was the phalanx, the formation used by the Greeks, Macedonians, and Carthaginians. For the Romans the phalanx proved to be too unwieldy a unit to fight on hilly and broken ground and they soon began to change the nature of their battle formations. The result was the legion. Unlike the phalanx, the legion was not a static form; it varied greatly over the centuries.

The term legion did not originally mean any specific type of military formation. Its origin probably denoted those who were chosen for military service during the annual public assembly of citizens. As it developed, the legion became a unit of from 4,000 to 6,000 heavy infantry supported by cavalry and light infantry. The term infantry simply means soldiers who fight on foot; the terms light and heavy refer to the kinds and weight of their weapons.

The advantage the legion had over the phalanx was flexibility and mobility. The legion did not have to move in a solid block of men as did the phalanx. The legion was divided into maniples, groups of 120 men, which were able to fight in a much more open and versatile battle array; they marched in lines instead of solid formation.

On the march soldiers carried weapons, armor, cooking gear, and tools. Each day the army would stop and build a camp surrounded by a wall of logs and a deep ditch. With the army went a train of baggage animals, armorers, supply staff, engineers, and secretaries.

From the earliest days of the Republic until the end of the 2nd century BC the armies of Rome were made up of citizens called up for duty each year. Every male citizen between the ages of 17 and 46 was liable for duty. In times of extreme emergency all male citizens could be called up, even the young and the aged. Each class of citizens had to furnish a specific number of companies made up of 100 men. These units were called centuries, or hundreds, and they were commanded by officers called centurions. Even after the units of one hundred were abandoned, the term centurion persisted as an officer designation.

Shortly before the end of the 2nd century BC a number of changes were made in the Roman army system that were to change the very nature of Rome itself. Reliance on an annual call-up of citizens meant that Rome never had a permanent army. This practice was abandoned. The citizen army was replaced by a standing army made up of landless city dwellers and newly created citizens from outlying provinces. The allegiance of these new legions was to their commander rather than to the Roman state. The commander was expected to pay his soldiers in money or land supplied by the state.

The leader in this reform of Rome's military system was the general Gaius Marius. He reformed the legion, substituting for the maniple a 600-man unit that was called the cohort. The soldiers swore an oath to him, binding them to service for a period of ten years. This transformation from a temporary citizen army to a professional one made better training possible. It also meant that each Roman commander had his own private army, with legions that were faithful to him for their term of service.

This new army system paved the way for the destruction of the Roman Republic and the establishing of the empire. Army commanders not only went abroad making new conquests and fighting barbarians, but also vied with each other for political control of the Republic. During the 1st century BC, Roman legions often fought each other under the leadership of such generals as Pompey, Julius Caesar, Mark Antony, and Octavian.

In the end, it was Octavian, later called Augustus Caesar, who defeated all his opponents and instituted imperial rule at Rome. Once in power, he revised the army system by cutting the number of legions from 60 to 28, requiring 20 years of service from the soldiers, and setting up a military treasury to pay the armies in the field and in retirement.

Under the empire the main task of the legions was not conquest, but defense. The extensive borders of the empire in Europe, the Middle East, and Africa had to be continually held against domestic insurrection and foreign invasion. Most of the legions were deployed at the outposts of the empire. More and more, the army's manpower was derived from conquered barbarians rather than Roman citizens.

In the 3rd and 4th centuries AD the army was again reorganized, first by the emperor Diocletian, and later by Constantine. The number of men in a legion was cut from 4,500 to 2,000 in order to gain mobility in fighting border wars. Total manpower was raised to 500,000, and discipline was strengthened. Constantine reorganized the legions into border guards and organized a mobile field army for a reserve force.

During the 5th and 6th centuries the western portion of the Roman Empire was overrun by invading barbarians. The center of power shifted to the Eastern, or Byzantine, Empire, with its capital at Constantinople. The Byzantine Empire was able to defend itself with a small, professional army consisting of barbarian mercenaries and landless peasants who volunteered as lifetime soldiers.

The organization

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 'handfulls', 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 cohortes, manipuli 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 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 posterior, princeps 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. A centurio 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 recieved 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 standardbearers. 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 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.

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