The organization and equipment of the Roman legion.


  Roman cavalry in action

The Battle of Mons Graupius AD 84. (Illustration by Jennifer Campbell from Antony Kamm, Scotland in Roman Times, Scottish Children’s Press 1998)

The Britons farther up the hill, who had until then taken no part in the action and had had time contemptuously to observe how small our numbers were, now began gradually to move down the hill in an attempt to outflank the advance, wheel round, and attack from behind. Agricola, who had anticipated this manoeuvre, called up the four cavalry squadrons that he had kept back in case of emergency. So furiously did they charge against the oncoming opposition, that what was intended as a push forward disintegrated into a rout. The tactics of the Britons now rebounded on them, as at Agricola’s command the cavalry squadrons in the thick of the battle disengaged, rode round the packed enemy lines, and took the Britons in the rear. Tacitus, Agricola, 37.

The Roman talent for organization is nowhere better illustrated than by its army, the backbone of which was that epitome of the professional fighting man, the legionary. After the civil war, Augustus created a standing army of twenty-eight legions, at which strength, give or take the odd legion, it remained for two hundred years.

Roman soldiers

(Illustration by John Pittaway from Picture Reference Ancient Romans, Brockhampton Press 1970)


Legionary HQ

Model of legionary headquarters. (VRoma: Chester Museum: Barbara McManus)

Under the republic, new legions were assigned a serial number, numbers I to IV being reserved for those raised by consuls. Whatever the system, and it is not fully understood, at any one time several legions might have the same number. To avoid confusion, each came to assume also a title or nickname, reflecting the circumstances of its formation, the name of its founder, the place where it was raised, or the front where it had served with distinction.

A legion’s own standard, often referred to as its “eagle”, was carried wherever it went. The eagle was the rallying point for troops in battle and a signal as to where the action was; to lose it to the enemy was both a disaster and a disgrace.


Bronze coin of Caligula commemorating his father Germanicus holding a staff topped with the eagle. The inscription refers to his having recovered the standard from the Germans. (VRoma: British Museum: Barbara McManus)

The aquilifer, who carried the legion’s standard, ranked in seniority only just below a centurion and was responsible for the safe-keeping of the legion’s pay chest. The imaginifer carried an image of the emperor. Standard bearers wore animal skins with the heads drawn up over their helmets.

A legion was a self-contained unit which even on the march could rely on its own resources for weeks on end. The legionaries themselves did all the manual work of digging, construction, and engineering. Every man carried trenching tools and a pair of stakes which at each stop became part of the camp palisade. He also had to shoulder, or carry attached to his person, clothes, a cooking-pot, rations, and any personal possessions, as well as his weapons and armour.


Surveyor on the march using a groma; having planted it in the ground and checked from the plumb lines that it was upright, he would take a sight along the arms or strings to make a straight line or right angle. (Illustration by Jennifer Campbell from Antony Kamm, Scotland in Roman Times, Scottish Children’s Press 1998)

Each legion had a complement of specialists and craftsmen: surveyors, medical and veterinary orderlies, armourers, carpenters, hunters, even soothsayers. The surveyors went ahead of the column of march to select and lay out the site of the night’s camp; it was always constructed to the same pattern and surrounded by a ditch, a rampart, and a palisade, all of which had to be built afresh each time. Leather tents, each of which slept eight men, were carried separately by mules.


Battle scene from Trajan’s column (cast), with (bottom right) medical orderlies tending the wounded. (VRoma: EUR (Rome), Museum of Roman Civilization: Barbara McManus)

In the field, a legion comprised ten cohorts, each divided into six centuries of eighty men, under the command of a centurion. The commander of a legion (legatus) held his post usually for three to four years; he was assisted by six younger officers, the military tribunes, who also were political appointees. The senior professional officer in the legion was likely to be the praefectus castrorum. He was usually a man of some thirty years’ service, and was responsible for organization, training and equipment.

Day-to-day responsibility was therefore in the hands of the centurions, the most senior of whom (centurio primi pili or primus pilus) commanded the first century of the first cohort.

Centurion, aquilifer and signifer

(Left) centurion; (centre) aquilifer; (right) signifer, who carried the century’s standard and looked after its savings bank. (Left and right, illustrations by Jennifer Campbell from Antony Kamm, Scotland in Roman Times, Scottish Children’s Press 1988; centre, illustration by John Pittaway from Picture Reference Ancient Romans, Brockhampton Press 1970)


The legions were supported by auxiliary forces, composed of inhabitants of the empire who were not citizens of Rome. All cavalry were auxiliaries. While some auxiliaries fought as infantry and were equipped like legionaries, others retained their native dress and weapons, serving as archers, slingers, spearmen, or broadswordsmen. Originally auxiliaries were led by their own chiefs, but in imperial times they were brought within an overall chain of command under Roman officers.


Drawing of auxiliary cavalrymen and horse. (VRoma: Landesmuseum, Mainz: Barbara McManus)

Under the empire, the only armed forces in Italy were the imperial guard, and the cohortes urbanae (city cohorts), who garrisoned Rome itself and whose presence was to prevent unrest rather than ward off possible attack from outside. The imperial guard was a crack unit whose members wore special uniform and received double pay. When the emperor went on campaign, the guard went with him. A further force, the vigiles, recruited from freedmen, patrolled Rome itself and served as its fire brigade.

imperial guard

A relief in the Louvre, Paris, from the period of Trajan and Hadrian, showing members of the imperial guard, indicated by their rich uniforms and helmets, and oval shields. Behind is a legionary standard, with the eagle holding a thunderbolt in its claws. (Deutches Archaeologisches Institut, Rome)

Up to the time of Augustus, mastery of the seas had been achieved by ad hoc methods and largely foreign naval skills and crews - no Roman citizen ever handled an oar. Augustus established a standing fleet of ships which were his own property and which he manned with freeborn provincials and his own freedmen. His successors saw the wisdom of his initiative, and under the emperor’s overall command there were established ten regional flotillas. The British flotilla, based at Boulogne, was used by Agricola in AD 83 to soften up the opposition in Scotland with lightning raids up the east coast; it also (according to Tacitus) discovered the Orkney islands and established conclusively that Britain was an island.


Coin of Hadrian showing Roman naval vessel with oars and rowers. (VRoma: British Museum: Barbara McManus)


Legionary chart

Roman legion chart

From Antony Kamm, Julius Caesar: a beginner’s guide, Hodder and Stoughton 2002

Length of service

Augustus increased the length of service for soldiers to 16 years, with a further four years on light duties. Army auxiliaries served for 25 years, after which, from the time of Claudius, they were entitled to Roman citizenship. Navy men served for 26 years.

The eagles are lost!

The eagle recovered by Germanicus in AD 15 belonged to one of the three legions (Seventeenth, Eighteenth, Nineteenth) which were lost six years earlier under Varus (full account here). All three standards were eventually recovered. One of the most distinguished legions to lose its eagle was the Fifth Alaudae (Larks) in Gaul in AD 17. This legion was raised by Caesar in 52 BC, primarily to protect his province of Cisalpine Gaul, and served with him during the rest of his Gallic campaign and during the Civil War. For its bravery and effectiveness when facing the Pompeian elephants at Thapsus in 46 BC, it was awarded an elephant as its permanent emblem.

The imperial guard

Under Augustus the imperial guard (cohors praetoria) consisted of 9 cohorts each of 500 men, with a cavalry arm, equites singulares Augusti. Septimius Severus raised the number in each cohort to 1000. The imperial guard came to play a leading role in emperor making, to the men’s advantage - it was usual for a new emperor to promise the guard a “bribe” equivalent to five years’ pay.

Believe it or not:

Riders in the ancient world did not use stirrups, which were not widely adopted in Europe until the eighth or ninth century. Roman cavalrymen were required to vault straight into the saddle, which Arrian (c. AD 86 - 160) claims they could do in full kit while the horse was at a canter.

The idea of a mobile strike force is not new. Severus appointed his Second Legion (Parthica) to this role. Based in Italy, it was to be deployed wherever it was required.