Legion

Шиманович А.А.

A legion was the main tactical and organizational unit of the Roman army. In the Principate a full legion is usually described as a force of about 5,000-6,000 men, divided into cohorts, centuries and contubernia; real strength depended on date, losses, recruitment and campaign conditions.

In brief:

a legion had ten cohorts;
a normal cohort contained six centuries;
a century was commanded by a centurion;
a contubernium was a tent group of about eight soldiers;
a legion was not only a battlefield formation, but also an administrative, engineering and marching organization.

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legion meaning / what was a Roman legion	A legion was the main large formation of the Roman army. In the classical period it consisted of cohorts and centuries and had its own commanders, standards, heavy infantry and support needed for long campaigns.	Cohort, Century, List of Roman legions

A legion should not be treated as one fixed number of soldiers for every period. Its size, structure and equipment changed from the Republic to the late Empire.

Common follow-up questions

Was a legion the whole Roman army? No. A legion was a major part of the army, but auxilia, fleets, garrisons and other forces also existed.

How many men were in a legion? Usually several thousand soldiers, but the exact number depends on period and the condition of the unit.

Legion structure in numbers

Unit	Usual strength	Role
Contubernium	About 8 men	Tent group
Century	About 80 men	Basic tactical unit
Cohort	About 480 men	Main legion subdivision
Legion	About 5,000-6,000 men	Large army formation

Legionnaires of Legio X Fretensis. Reconstruction

The Structure of a Legion

A legion’s organisation is easiest to follow from its smallest units upwards:

Contubernium: a tent group of about eight soldiers.
Century: a basic tactical and administrative unit commanded by a centurion.
Cohort: a group of centuries; a legion of the Principate normally had ten cohorts.
Legion: a formation with infantry, officers, standards, a baggage train and specialist personnel.

Actual strength varied with period, recruitment and losses. Figures of roughly 4,800–6,000 men are commonly used for an early imperial legion, while some late Roman legions were substantially smaller.

The Development of the Legions

The Army of Regal Rome

Roman tradition traced the legion back to the earliest days of the city. Under the Roman kings, the term referred to the citizen levy rather than a permanent formation of the later imperial type. It is associated with the Latin verb legere, “to gather” or “select”.

Traditional accounts describe a force of about 3,000 infantry with a smaller mounted contingent, recruited through the city’s early social divisions. Exact figures and battle formations cannot be securely reconstructed for this period. Ancient writers attributed major changes in recruitment and organisation to Servius Tullius, traditionally dated to the sixth century BCE.

The Reforms Attributed to Servius Tullius

The so-called Servian system linked military obligations to property and age. Citizens with sufficient wealth were expected to provide their own equipment. Younger men formed the main field force, while older men were more likely to serve in local defence or the reserve. Ancient accounts associate this system with the organisation of citizens into centuries and with heavy infantry fighting in a phalanx.

The division into younger and older citizens gave the system an age-based as well as a property-based structure: men available for field service and men primarily assigned to home defence did not have identical obligations. Because the surviving narratives were written much later, the institutions they attribute to Servius should not all be dated with equal confidence to one reign.

In the traditional account, wealthier citizens supplied heavily equipped infantry with helmets, body armour, shields, swords and greaves. Poorer classes carried progressively lighter equipment, including spears, javelins, slings and stones. These property-based centuries should not be assumed to have had the fixed strength or organisation of centuries in the later legion.

Livy’s account assigns eighty centuries of infantry to the wealthiest class, half younger and half older men. It describes five property classes, followed by the poorest citizens below the normal qualification, rather than six equally equipped infantry classes. The higher classes provided heavier arms; the fourth is associated with spears and javelins, and the fifth with slings. The political centuries of the census must also be distinguished from later tactical units of nominally fixed size.

The Legions of the Early Republic

Under the early Republic, military command was divided between the consuls. The levy expanded as Rome’s wars became more frequent, and the conventional consular army eventually comprised two Roman legions for each consul, accompanied by allied forces. Soldiers received pay, although service remained an obligation of citizenship rather than a modern salaried career.

During the middle Republic, the phalanx gave way to the more flexible manipular legion. This development is often discussed in connection with the Samnite Wars, although its exact course is uncertain. A legion contained thirty maniples of heavy infantry, each divided into two centuries under centurions. Their strength varied by troop category. A mounted contingent, conventionally about 300 men, was divided into turmae.

Italian allies supplied separate infantry and cavalry formations. These Republican allied contingents should not be confused with the later imperial auxilia and their system of long-term service and citizenship grants.

Polybius’ second-century BCE description gives a normal legion 4,200 infantry, increased to 5,000 in exceptional danger, and 300 cavalry. It has ten maniples in each of the three heavy-infantry lines. In the standard 4,200-man arrangement, hastati and principes each number 1,200, the triarii 600, and the remaining 1,200 are velites. Thus the triarii maniples are smaller than those in the first two lines. The cavalry is divided into ten turmae of about thirty men.

The heavy infantry was divided into hastati, principes and triarii, supported by light-armed troops known as velites. This differed from the earlier hoplite model. The scutum became characteristic of Roman infantry, replacing the round hoplite shield in many contexts. Hastati and principes carried pila, while the triarii retained thrusting spears.

Order of battle of the legions of the early Republic

The maniples were conventionally arranged in three lines: hastati in front, principes behind them and triarii in the rear. Age and experience helped determine a soldier’s place. The triarii represented a final reserve, reflected in the saying res ad triarios rediit—“it has come down to the triarii”.

Velites skirmished ahead of the heavy infantry with light javelins before withdrawing through the formation. The cavalry protected the flanks and performed other mounted duties.

The manipular system is associated with the First and Second Punic Wars. Over time, the larger cohort became increasingly important as a tactical unit.

Legionnaires of the early Republic - Hastatus,Velitus,Triarius,princip

The Legions of the Late Republic

From the late second century BCE, the cohort increasingly replaced the maniple as the principal tactical unit. The process is often associated with Gaius Marius, but it should not be treated as a single, fully documented reform. Commanders and their legates adapted organisation to the needs of prolonged campaigns.

A cohort of six centuries is conventionally reckoned at about 480 men, but actual strengths depended on recruitment, casualties and detachments. The old distinction between hastati, principes and triarii gradually disappeared, and equipment became less closely tied to a soldier’s property class. Cohorts could deploy in several lines, giving commanders flexible reserves.

Diagram of legionary divisions from the late Republic to the beginning of the third century AD

Longer campaigns and the recruitment of men with little property encouraged the development of a more professional army. Service was increasingly attractive as a livelihood, but compulsory levies did not simply vanish. Legionary recruitment remained closely tied to Roman citizenship.

Equipment became more consistent without becoming completely uniform. Mail armour, the scutum and the pilum were characteristic components of late Republican legionary equipment. Provisioning and replacement increasingly depended on organised military supply as well as individual arrangements.

The Legions of the Principate

The civil wars that ended the Republic greatly increased the number of legions. Many soldiers developed strong personal ties to their commanders, whose success could determine their pay, rewards and prospects after service. The creation of the Principate brought a major reorganisation of these forces.

Octavian Augustus - first Roman Emperor

Augustus discharged many veterans and established a smaller standing army of numbered and named legions. Their titles reflected origins, honours and associations with particular commanders or emperors. Under his successors, changes in equipment included the use of lorica segmentata alongside mail and scale, as well as developments in shield construction and shape.

Legionnaires of the I-II century period on a campaign. Reconstruction

The legions were central to the expansion and defence of the Roman Empire during the first and second centuries CE. Training, engineering, supply systems and communications made them effective campaigning forces, although they were never invulnerable to defeat.

Roads supported the movement of troops and supplies. Soldiers also built and maintained infrastructure. Permanent fortresses and camps defended strategic areas and encouraged the growth of settlements around them.

The Late Roman Legions

The third-century crisis combined civil wars, external attacks, epidemics and economic disruption. These pressures transformed the army as well as the wider state. The late Roman army differed substantially from its early imperial predecessor in organisation, deployment and equipment. These changes continued under the Dominate.

By the fourth century CE, new helmet forms were in use and lorica segmentata had largely disappeared. Mail and scale armour remained important. Round and oval shields were common in place of the familiar early imperial scutum.

Spears such as the hasta and longer swords such as the spatha became characteristic, while the shorter gladius was less prominent. Vegetius also describes greaves for soldiers in the front ranks. Missile weapons included forms related to the pilum, lighter javelins and lead-weighted darts known as plumbatae.

Many late Roman field legions were smaller than early imperial legions, often estimated at around a thousand men, although unit strengths varied widely. Army formations included heavy infantry, archers and skirmishers. Cavalry and specialist units operated alongside the infantry within larger field armies.

Late Roman legionnaire with spear and shield

Legionnaire of late Rome with a bow

Cavalry played an increasingly important role in reconnaissance, pursuit and battlefield manoeuvre. Infantry remained the foundation of many battle lines. Soldiers could combine missile fire with close-order formations of shields and spears, supporting mounted operations while retaining their own offensive capabilities.

Roman legions of late Rome in battle

Late Roman forces remained capable of major victories during the third and fourth centuries. The eventual collapse of imperial rule in the West cannot be explained simply by supposedly inferior equipment or tactics: political fragmentation and the loss of resources undermined the ability to maintain effective armies. The Eastern Empire continued to adapt Roman military institutions long after the end of western imperial rule.

Officers of the Legion

Ranks and responsibilities changed over time. The following outline describes the command structure commonly associated with a legion of the first and second centuries CE.

Senior Command

The legatus legionis commanded the legion. This office was distinct from that of a military tribune and from the broader provincial governorship, although responsibilities could overlap in particular circumstances.

The senior tribune, the tribunus laticlavius, was a young senator. Five tribuni angusticlavii came from the equestrian order. The praefectus castrorum, or camp prefect, was normally a highly experienced former senior centurion responsible for important practical and administrative aspects of legionary life.

The tribunus laticlavius ranked above the five equestrian tribunes even though his senatorial career might give him less practical military experience. The camp prefect brought a different kind of authority: knowledge acquired through years of service, often after holding the post of primus pilus. A provincial legatus Augusti pro praetore could command the province’s forces, including more than one legion, whereas a legatus legionis held command of an individual legion.

Centurions

1. The primus pilus was the senior centurion of the legion, serving in the first cohort. It was a prestigious post that could lead to further advancement, including equestrian appointments.

2. A centurion commanded a century and supervised its training, discipline and daily duties, as well as leading it in battle. Many rose through the ranks, although other routes of appointment existed. The number and arrangement of centurions varied as the legion’s organisation changed.

Junior Leaders

1. Optio: the centurion’s deputy, selected to help maintain order and able to take over if the commander was wounded or killed.

2. Tesserarius: a soldier responsible for duties connected with the watch and the distribution of passwords, helping organise security in camp.

3. Decanus: the leader associated with a small contubernium, usually a group of eight soldiers sharing a tent in the early imperial army. The term and the size of such groups should not be assumed to remain identical in every period.

4. Decurion: an officer associated with a cavalry turma, conventionally a unit of about thirty riders in Republican descriptions.

Standard-Bearers and Musicians

1. Aquilifer: the bearer of the legion’s eagle. Protecting the eagle was a duty of exceptional symbolic importance; its loss was a profound disgrace.

2. Vexillarius: the bearer of a vexillum, a cloth standard used by military formations and detachments.

3. Signifer: the bearer of a signum. These standards could carry discs, wreaths and other devices, sometimes compared with phalerae. Signifers also had financial responsibilities within their units.

4. Bucinator: a military musician who sounded the bucina.

5. Tubicen: a trumpeter who played the straight tuba. Musical signals helped transmit orders during military activities.

The eagle represented the legion’s honour and collective identity, but losing it did not automatically lead to the unit’s disbandment. A vexillum could identify a detached force as well as a larger formation. Signa commonly carried metal discs and other ornaments; not every disc should be interpreted as a specific award. Hand-shaped finials and wreaths contributed to the standards’ symbolic language. Musicians accompanied military activities in camp, on the march and in battle, allowing commands and signals to reach men who could not hear a spoken order.

FAQ

How many soldiers were in a legion? Strength varied, but for the Principate about 4,800-6,000 men is often used depending on structure and recruitment.

How is a cohort different from a century? A century was a smaller tactical unit under a centurion, while a cohort grouped several centuries.

Were all legions identical? No. Composition, strength, experience and attached specialists depended on period, province and mission.