How did Marius Reform the Roman Army?

The Marian reforms were ancient Roman army changes established in 107 BC by the politician Gaius Marius. The Roman Army was named after Marius.

The changes arose in response to the Roman Republic’s military and logistical stagnation in the late 2nd century BC. 

Centuries of military combat around the Mediterranean and growing invasions and uprisings throughout the Roman territory had strained the Roman army’s personnel and physical resources.

Gaius Marius was a Roman commander and politician who lived from 157 BC until 13 January 86 BC.

He held the post of consul an unprecedented seven times throughout his tenure, having won the Cimbric and Jugurthine wars. 

He was well known for his significant improvements to the Roman forces. He established the precedent for the transition from the middle Republic’s militia levies to the late Republic’s professional soldiery. 

He also improved the pilum, a javelin, and made large-scale reforms to the Roman army’s logistics system.

Marius, born into a prosperous provincial Italian family in Arpinum, had his first combat experience while serving with Scipio Aemilianus during the Siege of Numantia in 134 BC. 

In 119 BC, he was elected tribune of the plebs and enacted legislation to minimize the aristocratic influence in elections. After being elected praetor in 115 BC, he became governor of Further Spain for the first time. 

While there, he battled against outlaws. He married Julia, Julius Caesar’s aunt, when he returned from Spain.

Marius suggested dramatic changes to create a more professional, permanent, and energetic Roman army.

The reforms transformed the Roman military machine by creating the standardized legionary and cohort units and radically altering the property and armament criteria for enlistment. 

Due to the changes, the general is also responsible for equipping and managing an army. Marius also awarded all Roman troops citizenship and land. 

Consequently, these changes substantially influenced Rome’s military superiority and contributed to the Late Republic’s social and political turmoil.

These developments stayed primarily intact until the Roman Empire’s demise, although there were structural and administrative alterations, most notably by Augustus and subsequently by Diocletian.

What did Marius achieve?

Gaius Marius was one of the Roman Republic’s most prominent leaders. He was elected consul seven times in a row.

He also made significant modifications to the Roman army, altering Rome’s destiny and transforming it into the world’s most powerful civilization.

How did Marius deal with the Roman army’s personnel shortage?

Due to a lack of personnel, Marius broke with tradition by recruiting volunteers from outside the propertied classes, which had hitherto been the only ones liable for duty.

How did Marius die?

Marius received his prophesied seventh consulship, which was more than any Roman had ever had, but his time was cut short.

After just a few days, his mind and body started to deteriorate, and by mid-January 86 BCE, he died, supposedly of pleurisy, at the age of 70.

The Pre-Marius Roman Army

Level of the army, detail of the carved relief on the Altar of Domitius Ahenobarbus
Level of the army, detail of the carved relief on the Altar of Domitius Ahenobarbus

The pre-Marius Roman army was structured similarly to the Greek Poleis as a conscript levy of all male citizens.

When necessary, the sitting consuls would summon an army chosen by lot via a procedure known as the Dilectus. 

When a campaign was declared, it was considered the obligation of every physically capable man to serve in the army.

Drafted soldiers were organized into four legions, each formed yearly; they were subjected to intense training before starting a war. 

While on the campaign, the soldiery earned experience, but they were dissolved after the war or the campaigning season. As a result, with the conclusion of the conflict, all competing in the Roman army were lost. 

Like those in Hispania and Macedonia, Garrison forces were discharged at the commander’s discretion.

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Soldiers were poorly paid, if at all, and salary delays were infamously prevalent. As a result, the main form of remuneration was pillage and plundering shares.

Even the ordinary soldier had to meet severe property and census conditions to join the pre-Marian Roman army:

He must be in the sixth census class or above (the adsidui, or “tax-payers”). He was required to possess property worth 3,500 sesterces. And finally, he had to provide his weapons.

These restrictions evolved. Only those with total assets of 10,000 asses or more were eligible to serve in the military by the Second Punic War.

This method of citizen-soldiers bringing their equipment of at least equivalent caliber worked effectively as long as the conflicts were brief and fought close to home.

With the rapid development of the Roman territory, wars grew more lengthy, frequently lasting several years. 

Small farmers who had left their homes to battle sometimes faced a disaster due to such exceptionally extended duty lengths.

The use of census, property, and armament requirements also resulted in a division among Roman census classes (as opposed to the usual plebeian/patrician divide). 

Each legion comprised four streamlined unit types (reflecting how much profit the soldier could invest in his arms and armor) (the velitas, hastati, principes, and triarii).

These troops functioned within the maniple system, which had evolved in the 320s BC as an alternative to the standard ‘Italic’ phalanx.

The troops in this formation were divided into several lines depending on age, experience, and wealth:

The Velites

A veles in combat
A veles in combat

The poorest (5th class proletarii) and frequently the youngest citizens cannot purchase a shield, helmet, armor, or even a gladius. 

They were unarmored javelin-throwing skirmishers who approached the front of the Roman line of combat and fired their missiles to confuse the enemy while the hastati advanced. 

They then fled rapidly through the lines to the rear. They were not anticipated to hold any part of the fighting line, nor were they equipped.

The Hastati 

Hastati roman army full set
Hastati roman army complete set

They were fourth-class people who could afford rudimentary armor, a small shield, and a gladius.

The hastati, the pre-Marian legion’s first rank of heavy (technically medium) infantry, were supposed to maintain the front of the line in the heart of the fight. 

They were mainly youthful and active men of the middle to lower-middle class. Their lighter armor and front-line position invariably resulted in the heaviest deaths in each fight. 

But strong performance (and survival) earned advancement to the principes and higher social mobility in peace.

The Principes 

Roman legionary from the principes
Roman legionary from the principes

Principes were third-class people who could purchase a complete suite of high-quality armor, a giant shield, and a bronze helmet in conjunction with their swords.

The principes were the pre-Marian force that nearly resembled the conventional legionnaire that the Marian reforms would ultimately create. They were considered the heart of the pre-Marian legion.

They positioned themselves just behind the hastati and substituted them in the front line if they could not breach the opposing formation on their own, which was usual. 

Allowing the opponent to exhaust themselves on the lighter hastati before confronting the principes was generally practical.

The Triarii 

Triarius metal armor at the Flavian Amphitheater, Rome
Triarius metal armor at the Flavian Amphitheater, Rome

The last infantry unit, the triarii, was limited to seasoned principes veterans and anchored the whole Roman battle line.

The triarii were regarded as the elite infantry of the pre-Marian legion, fighting in the manner of hoplites in the rear of the formation. 

They were not typically used. Instead, they were utilized as a last option if the hastati and principes could not breach the enemy line and were forced to flee.

The phrase ad triarios redisse (“to fall back on the triarii”) was employed to describe a last, valiant effort to save a terrible situation.

The Equites 

Equites, agile cavalry
Equites, agile cavalry

Equites were agile cavalry who wielded a one-handed light spear. They were affluent individuals of the equestrian class who could purchase a horse. 

They often moved around the infantry line’s flanks, breaking up opposing skirmisher and missile groups and pursuing troops the infantry had defeated.

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They were also the principal scouting element for the legion. 

Marius as a Consul in the Roman Army

Bust of Marius instigator of the Marian reforms
Bust of Marius, instigator of the Marian reforms

Once the patricians had formed an army, one of them would usually lead it into combat. Not all appointed consuls were capable of commanding an army.

In 113 BC, for example, the consul Gnaeus Papirius Carbo was beaten at the Battle of Noreia by raiding Cimbri and Teutonic tribes. 

Following that was a lengthy battle in Africa versus King Jugurtha of Numidia. Quintus Caecilius Metellus Numidicus was dispatched to defeat Jugurtha. He had not won ultimate triumph after two years. 

One of his legates, Gaius Marius, begged that Metellus remove him from his responsibilities so that he may rejoin Rome and run for consul at the end of 108 BC.

Marius had no army when he became junior consul in 107 BC and was tasked with bringing the conflict with Jugurtha to a close.

The army Metellus had led in Africa was sent to the senior consul, Lucius Cassius Longinus, to drive the Cimbri.

They were invading the Roman province of Transalpine Gaul once again (Gallia Transalpina). 

Marius had no men to fight the war in Africa because the eligible populace from whom he might raise an army had been badly reduced by past military disasters and the latifundia’s growth at the cost of small landowners. 

It was evident that a transitory army based primarily on rigid qualifying rules resulted in a restricted quantity of recruits and short-term military shortages. To address this issue, he implemented a variety of measures.

The Marian Reforms 

Relief scene of Roman legionaries marching, from the Column of Marcus Aurelius, Rome
Relief scene of Roman legionaries marching from the Column of Marcus Aurelius, Rome

The incorporation of the Roman landless masses, the capite censi, and men without property to be evaluated in the census was the most important Marian reform.

They were instead “counted by the head.” The males were now among those who could be recruited even though they owned no considerable property. 

Marius planned for the state to distribute arms to the impoverished people since they could not afford to buy their weapons and armor.

As a result, he gave the disaffected masses permanent work for pay as professional troops and the potential to acquire war spoils. 

With few other options for achieving prestige, the people rushed to join Marius in his new army.

Furthermore, professional soldiers were recruited for a 16-year enlistment period, which was eventually increased to 20 years’ whole duty and five years as evocati under Augustus’ reforms. 

Relaxing the property restrictions and giving high-quality equipment (rather than depending on an individual’s pre-existing riches) significantly boosted the availability of recruits.

As a result, the size of the Roman army. For the first time in Roman history, impoverished Roman citizens were permitted to serve in the Roman military.

Each soldier had to furnish their equipment under the previous system, but with the new massive number of impoverished troops owing to the other Marian reforms, this could not continue.

Marius modified the system by delegating responsibility for army provisioning to the general. 

Roman troops had to carry their supplies, weapons, and meals for many days. The century brought all the weapons and accessories needed to feed and sustain it. As a result, they were dubbed “Marius mules.” 

These logistics shifts significantly decreased the size of the baggage train necessary for support, allowing the army to be considerably more flexible.

This was likely a practice that existed before the Marian reforms and was merely reinstated, implying that the Marian reforms just restored this tradition.

Marius’s second major reform was the establishment of a permanent army. Marius was skeptical of the army’s volunteer organization, which dissolved after a short duty period.

Alternatively, he established career troops with a fixed job and regulated training and equipment. 

Drilling and training went done throughout the year, not simply when war was imminent.

The uniformed and rigorously schooled legionary became the cornerstone of the Roman army, thanks to the increasingly standardized equipment.

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Marius reorganized the Roman legion from a maniple system into cohorts. A full-strength legion consisted of around 4,800 troops.

A legion’s internal structure consisted of ten cohorts of six centuries each. The century was headed by a centurion and comprised 80 troops. 

Each century was split into ten contubernia, each commanded by a decanus. There were eight legionaries in the contubernium. The century fought as a group, marched as a group, and camped as a group.

An army comprised of two to six legions organized together. Constant training maintained the legions in peak physical form and discipline, making them among the greatest in the ancient world.

The cohorts were deployed in a condensed line to promote morale and discipline than the preceding maniple line.

Marius was able to pass legislation that provided savings benefits in the guise of land rights as the third reform.

Members of the number of attendees who had finished their term of duty would be awarded a pension. 

They would also be awarded a piece of land in the captured province to settle on by their general. Officers and commanders received monetary prizes 10 to 25 times a regular foot soldier.

Finally, Marius offered the people of the Italian allies (Etruria, Picenum, etc.) entire Roman nationality, provided they fought for Rome and served in the Roman army for a length of time.

Marian Reforms’ Impact on the Roman Republic

Ahenobarbus relief
Ahenobarbus relief

The earliest and most evident impact was an increase in the army’s military capabilities.

When war loomed the Republic, a general no longer had to rush to assemble a citizen army, prepare it to fight and follow military instructions and discipline, and then march it off to combat, raw and un-blooded. 

This was critical to the expansion and effectiveness of the Roman military. It resulted in the Romans’ ongoing victory on the battlefield.

Furthermore, establishing a competent standing army was better adapted to governing the expanding empire

It boosted the speed with which Rome could deploy forces. Generals in the Marian legion had to deal with fewer leaders, allowing them to deliver more sophisticated instructions to the army.

Another advantage of the reforms was the relocation of retired legionaries to conquered territory.

This aided in the region’s integration into a Roman province and “Romanization,” lessening dissatisfaction and resistance against Roman control.

However, the allegiance of the legions changed away from the Roman state and to other commanders who headed the army. Soldiers now had a clear financial interest to support their generals’ aspirations. 

It became too usual for a general to extend his imperium by using the troops to sway the senators and solidify his authority. Some went so far as to wage war on their political opponents, resulting in civil war.

This eventually resulted in the fall of the Republic and its transition into the Roman Empire, ruled by an emperor. 


Marian legions refer to the cohort divisions of the late Republic and early empire. Following the Battle of Vercellae in 101 BC, Marius awarded Roman citizenship to all Italian troops. 

He excused his actions to the Senate by claiming that he couldn’t distinguish between a Roman and an ally in the heat of combat.

This essentially ended the concept of allied legions. All Italian legions would henceforth be recognized as Roman Legions.

Auxilia, or contingents of allied/auxiliary warriors, would ultimately take over the job of allied legions.

Each legion had an Auxilia (auxiliary) similar to or similar in size, including specialized troops, engineers, and pioneers. 

It also included artillerymen and siege artisans, service and support groups, non-citizens (awarded Roman citizenship upon discharge), and undesirables

Light cavalry, light infantry or velites, and workers were common formations.

There was also a reconnaissance team known as speculatores, who may act as messengers or perhaps as an early sort of military intelligence agency. Each legion included ten speculatores. 

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