A Legion was made of various elements in Ancient Rome. They comprised of auxiliary forces (including archers, auxiliary infantry and cavalry), non-combatants, the Senior Legion officers, and the soldiers themselves. The standard legion during the early-Principate era of the Empire would have had ten cohorts, of which it would be further divided into six centuries, of which there were a further subdivision of ten contubernia (singular: contubernium).

Army Systems

Throughout the course of Roman history, the legions adapted to various changes in military tactics and in response to defeats and manpower shortages. During Rome's transitions from Kingdom to Republic, and then to an Empire, the legion (and army) underwent many changes over the centuries. Note that this section will deal mainly with the composition of the Roman legions excluding any auxiliaries and any soldiers from the Socii (allied Italian City-States during the Republican era or any other ally of Rome's).

Pre-Servian Army

Prior to the Servian Reforms, the Roman Army was much like that of the Greeks'. Rome had no standing army and one was only raised from the citizen body when posed with an external threat. Citizens levied to fight in the army were expected to provide for their own equipment and as a result, soldiers were limited by what they could equipment they could afford. Initially, the early Italic tribes in the peninsular fought in the same way any tribes would fight, with the younger and poorer members fighting as skirmishers or light infantry, and the wealthier, older and nobility fighting as medium or heavy infantry. Eventually, these tribes adopted elements from Greek warfare as Greek influence spread across the Mediterranean.  Similar to the Etruscan and Greek army models, the skirmishers and light infantry were comprised of the poorer citizens. These soldiers were usually ill-equipped, and depending on wealth, would sometimes have a shield and were armed with either javelins or slings (for the skirmishers) or light spears or swords (for the other variants of light infantry). The amount of armour varied from none to (at best) a small breastplate and if fortunate, a helmet. The skirmishers and light infantry were expected to act as a screening force for the heavier infantry, and were expected only to delay the enemy forces, not fight in a prolonged battle. The ranks of the heavier infantry and the cavalry were filled in by the wealthier citizens (usually the aristocrats - Patricians - or wealthy plebeians). The Roman heavy infantry of the era, influenced heavily by the Greeks and their neighbours, the Etruscans, fought in the style of the Greek hoplites. They wielded a long spear (probably similar to or the same as the three metre long dory spear) and a circular concave shield (similar or the same as the Greek aspis). Armour may have varied, though following the Greek hoplite model, would have worn a linothorax (linen and leather armour supported in design by iron scale mail) or a full bronze cuirass in addition to a bronze helmet, and bronze greaves. The shields would have been for the most part uniquely decorated/painted, each with different designs and colors to (usually) signify the city/city-state the soldier came from (a closely related analogy would be that of the Athenian hoplite bearing the painted image of an owl and olive branch on the shield). The cavalrymen would have come from the richest citizens (those would could afford horses and had the necessary prerequisite wealth) and would have been equipped similarly to the heavy infantry. The heavy infantry would form up behind the light infantry and would be the ones expected to do the fighting once the light infantry were pushed back. Meanwhile, the cavalry were expected to actively engage the enemy cavalry and destroy them, before wheeling around the flanks to charge the enemy line from the back.

The Servian Army

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Class Property* Equipment Juniores Seniores Total
1 100,000 Helmet, round shield, greaves, cuirass, spear, sword 40 40 80
2 75,000 Helmet, oblong shield, greaves, spear, sword 10 10 20
3 50,000 Helmet, oblong shield, spear, sword 10 10 20
4 25,000 Oblong shield**, spear, javelin 10 10 20
5 11,000 Sling, stones, javelin*** 15 15 30
  • Property was measured in terms of the As/Assarius (Plural: Asses/Assarii), a bronze (and later copper) coin used during the Roman Republic and Empire.
  • The only source for this piece of information is from the writings of Livy


  • The last class interchangeably carried javelins or slings and stones.

The Roman male population were divided in terms of property rating and further into senior and junior (they were further divided by age) centuries. The totals listed show the full number of centuries levied from each class. These men had to provide and/or purchase their own equipment, and those who did not meet the listed property requirements were not obligated to serve and were listed as only as part of the total number of soldiers. The chart lists only infantry units, and does not include the 18 centuries of cavalry, 2 centuries of engineers, 2 centuries of musicians, and other non-qualified civilians accompanying the army.


The Camillan Legion

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The Polybian Legion


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The Post-Marian Legion

The Marian Reforms instigated by the Consul Gaius Marius in 107 BCE was a response to combat the shortage of eligible citizens to serve in the army due to a series of defeats at the hands of migrating barbarian tribes (the Teutons and the Cimbri) and a prolonged war against King Jugurtha of Numidia in North Africa. The pre-Marian army during the majority of the Roman Republic had consisted of men being levied when war was announced, with types of infantry and roles being dependent on ownership of land (i.e. wealth), experience, and age. When war was announced, soldiers would be conscripted from those eligible for service and then these men would be demobilized once the campaign/war had come to its conclusion. With the problems facing Rome at the time, Marius turned to the abundant supply of urban poor and landless to construct his new army and instituted a set of reforms that would endure well into the Roman Empire. With the reforms instituted, Rome now had the first professional standing armies known to the western world.

Under the new system, soldiers would be sworn in and take an oath to the emperor while in the presence of the aquila (the sacred eagle standard of the legion) to serve Rome for a period of roughly 20 years (over the years, this number would fluctuate) before being discharged. The common footsoldier was not allowed to marry during this period.

Eligibility for Service

One of the first things that Gaius Marius did was to open enlistment to all able bodied men who were of age (around 17) regardless of class or wealth. This had a dual effect. Those of the Roman aristocracy were no longer required to enlist, while landowners did not have to risk their livelihoods because of forced conscription. Simultaneously, the lowering of class barriers effectively enabled the hordes of unemployed and poor proletariat to finally obtain a stable job, albeit a risky one. However, many of the urban poor and unemployed enlisted due to promises of treasure and land.

Legion Standards

The typical Republican legion had five main legion standard variants: the eagle, horse, boar, wolf, and minotaur. However, with the advent of the Marian reforms, all were replaced by the uniform usage of the eagle (aquila). Subsequently, the standard-bearer of the eagle would become known as the aquilifer. Under the command of the aquilifer were two other standard bearers known as the signifer and vexillarius.

A Professional Army

Previously, the standard Republican legion was based on a levy system, with citizens being recruited each and every time war broke out. They would then return to their land once the campaign had ended. This proved ruinous to many, especially landowners, who's crops (and essentially, livelihoods) would be ruined upon return. Marius' reforms re-established the legion as a professional standing military force. Now, instead of being forcibly conscripted, the ranks of the legions would be filled with full-time, career soldiers who trained continuously throughout all the seasons. These troops also did not have to purchase their own equipment, and under the reforms, would be supplied equipment and armour by the state.

Structural Changes

Marius did away with the previous maniple sub-units, creating a new unit called the cohort. Each cohort was to consist of six centuries, each century containing 80 uniformly equipped soldiers and 20 camp followers. Within each century were 10 contubernia, each contubernium led by a Decanus (squad leader). Six centuries made up one cohort (each century was lead by an officer called a Centurion) Ten cohorts (each cohort was lead by the highest ranking centurion in the cohort - usually the Centurion of the first Century) would form an entire legion. Usually, provincial governors or (during the empire) officers selected by the emperor (called a Legatus Legionis) led a legion. Each soldier would be armed and equipped with a gladius (sword), two pila (throwing javelins), a brass 'Coolus' or 'Montefortino' helmet, lorica hamata (chainmail armour), an oval scutum (shield), caligae (sandals), etc. Later, during the empire, the shields became more rectangular and there would be increased use of the famous lorica segmentata (armour with segmented bands of metal) and iron helmets.


Previously, Roman legions utilized carts and wagons to carry equipment and weapons. This proved a problem as it bogged down the speed at which legions could march/advance. Slow baggage trains were often a liability due to the slow progress of the army and the chance that enemies might destroy it and virtually stop a campaign before it had even started. Marius changed this so that soldiers would be responsible for carrying their own packs and gear, including entrenching and cooking tools, emergency rations and any personal effects. These would be carried over the shoulder in packs attached to a pole called a furca.

Changes to the Pilum (Throwing Javelin)

Marius slightly altered the pilum, the Roman legionary's throwing javelin, replacing one of the two iron rivets holding the spearhead to the pilum shaft. This change was made with the intention of having the pilum's point breaking upon impact. This would render enemies incapable of using the same pilum against the Romans, as had happened in the past. Gaius Julius Caesar would later change this, but instead choosing to make the iron under the point untempered, causing the point to bend upon impact.

Army of the Late Empire


The Heroes of Olympus

The Lost Hero

During Jason Grace's fight with Lityerses, Lityerses has a hard time fighting Jason because he is unfamiliar with Jason's fighting style. When questioned about it, Jason says he learned how to fight in the Roman style during Legion training.

The Son of Neptune

Percy arrives at Camp Jupiter, which is made up of the Twelfth Legion, the only known legion to still be active. It is also explained that the Twelfth were given special instructions to follow Western Civilization and help continue the Legion by recruiting Roman demigods and legacies. 

Reyna, praetor of the Twelfth Legion.

The Mark of Athena

When Annabeth Chase was escaping Charleston, with the map to go find Athena Parthenos, she ran into Reyna. Reyna told her if she let her go, the legion would be at war with Camp Half-Blood, and declare war on their camp. 


  • Each of the Roman Legions were given a standard that were blessed by the gods. The Twelfth Legion Fulminata, the only known Legion to survive to the present day were given the Eagle, blessed by Jupiter himself.
  • Prior to the Marian Reforms, Legion Standards could be any of the following: A(n) Wolf, Minotaur, Eagle, Ox, or Boar
  • The legions of the Republic (before the Marian Reforms) utilized a system of class. The poorest citizens would form the ranks of the Velites (javelin armed skirmishers) and Hastati (scarcely armoured legionaries), while the more experienced and older soldiers would form the ranks of the Principes (equipped with the Lorica Hamata or Squamata). Finally, the richer and oldest troops (usually in their prime - 30's) would form the ranks of the equites (cavalry) and spear-armed Triarii.
  • The legions of the Roman Kingdom were raised through the Etruscan and Greek levy system in which poorer citizens would form up (typically) spear/javelin wielding skirmishers and light infantry, while the richer citizens would form up as heavier infantry (typically Hellenistic-style Hoplites), and equites.