The Marian Legions

Rome re-invented its military system several times. After the Greek Phalanx, the Romans used two major army structures. The Polybian Legions of the Roman Republic and the Imperial Legions of the Roman Empire.

The two legions were structured differently. There was a transitional mid-point, in the Roman Army reforms instigated by Gaius Marius that paved the way for the Imperial Legion and marked the end of the Polybian Legion. The Marian legions, enhanced the power of each legion. Politically, it sped up the fall of the Republic.

Brief background:

Not every Roman citizen was eligible to join the Legions. Certain criteria had to be met before a citizen could serve. The criteria were:

  1. Had to be a member of the fifth census class (Roman citizen tier)
  2. Had to own property worth 3500 sesterces.
  3. Had to supply his own armaments

The third point decided what type of soldier the citizen would be. A Velite skirmisher, lightly armoured Hastati, the more heavily armed Principe’s, the elite reserves: Triarii or the Equites in the cavalry. The order is in ascending order of social classes and wealth, with Velites being poor citizens who could not afford armour, while the Equites were the richer sections of society.

Left to Right: The Hastati, The Velite, The Principe, The Triarii

As Rome expanded, it was forced into more conflicts. Casualties mounted. The current system couldn’t maintain large armies, and Rome needed them. The turning point was migration of the Cimbri and Teutones in Northern Italy, and the Jugurthine War in Africa. The former conflict saw several Roman armies annihilated.  The Jugurthine war tied down many soldiers. Rome’s existence was threatened as it lacked armies to defend itself.

Marius’s rise

Gaius Marius, a legate during the Jugurthine war was a ‘New man’ in the Roman elite. Disillusioned with the lackadaisical progress being made in the Jugurthine war, he returned to Rome in 108 BCE to run for Consul. He was elected, and focused on the Jugurthine War before facing the looming threat of the Germanics.

Gaius Marius
One of Rome’s greatest generals, Gaius Marius instigated these major reforms of the legions.

The Battle of Arausio, was a key battle in instigating his reforms. The consul Gnaeus Maximus was a ‘New Man’. His subordinate, Quintus Caepio, a patrician refused to cooperate. The ensuring battle saw 80,000 Roman soldiers killed. Rome had no armies or a pool of recruits. Luckily for them, the Germanic tribes went towards the Pyrenees, giving Rome respite.

The Battle of Arausio saw 80,000 Legionarries slaugtered

The Reforms

Marius recognized the need for maintaining a larger force and having a larger pool of men to recruit from. He abolished the property requirements and allowed the landless masses and urban poor of Roman territory to enlist. With no alternative for better income and advancement in society, many joined. Marius arranged for the state to supply armour and weapons. The soldiers were to serve 16 years before discharge with a plot of land, as a professional army. They would be paid a regular salary (in addition to war loot), while training and drilling all year-round. This improved the endurance and combat abilities of the legion.

The major changes that took place affected:

The Soldier.

The Polybian legion worked with the right balance of various troop types. However, during extended conflicts, imbalances disrupted the effectiveness of the legion. Legionaries were now equipped like Principes. The legionaries were standard heavy infantry men, armed with the short-sword as their primary weapon, 2 Javelins, a dagger, Chainmail armour, and a large oval shield.

The New Legionary: A well armed heavy infantry trooper


The maniple structure which defined the battle order was abolished. The new Roman structure centred on the cohort. A cohort was a force of 480 men. With standard troops and training, it was flexible in combat and could adapt to situations.

Polybian maniple
The Maniple order of Battle

The smallest unit was the Contubernium. It consisted of 8 soldiers and 2 helpers (to look after armour, and supplies for them). They were led by a soldier amongst them called the Decanus. At the next level, 10 Contubernium formed a force of 80 soldiers and 20 helpers, called the century. This was in fact the most basic tactical unit, and was led by an officer, the Centurion.

6 Centuries made a cohort of 480 men, the primary sub-unit of the legion. There were 10 cohorts, with 9 regular cohorts the first cohort of the legion, with 5 double-strength centuries for 800 men and were the best troops in the legion.

Marian Legion
The Marian and Imperial legions were organized similarly. A Double strength first cohort, 9 cohorts of 480 men.  The imperial legion would later add the cavalry arm.

In support, auxiliaries were recruited from various lands to fill specialized roles. These included archers, slingers, light infantry and cavalry. Rome recruited Balearic Slingers, Cretan Archers, Numidian Cavalry, Gallic Infantry and Germanic Cavalry among others.


The logistics of the legion was overhauled. Armies have always been slowed down by their supply train. In order to reduce his supply trains and speed up his forces, Marius made his troops carry their own armour, basic cooking and camp equipment and 15 days rations. That was 60lbs of weight. A forked stick was issued to help ease the load. The soldiers were nicknamed Marian Mules.

Marius mule.jpg
Marian Troopers carried a lot of gear, including food and weapons and some basic camp equipment.

There were two outcomes from this change. Carrying such load while marching, helped improve the conditioning and stamina of the soldiers. Secondly, the Legions could make forced marches on short notice for short periods of time, without their main baggage train. This led to opportunities to surprise regrouping enemies by engaging them at short notice. The legions would have just been accompanied by mules carrying equipment, with 10 legionaries sharing a single mule.


The Romans now possessed a large citizen pool to form their armies. The training and discipline instilled made them a more formidable fighting force which would help them expand into Gaul, Britannia, Africa, etc. However, there was a downside. The legionaries, while nominally swearing allegiance to the senate, had their loyalties firmly tied to their generals. This would see them willingly fight fellow Romans during the civil wars in the last century of the Republic. The Marian legion helped strengthen the Republic’s military, but also helped paving its downfall.

Roman civil wars
With Legionaries now being utterly loyal to their generals, many used them during the civil wars that ended the Republic. Generals like Marius, Sulla, Caesar, Pompey, Marc Anthony, Octavian would use them without remorse as the Republic fell within a century of Marius’ reforms.

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