The Roman Army of the Roman Republic

Roman army
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The Roman army (exercitus) did not start out as the superlative fighting machine that came to dominate Europe to the Rhine, parts of Asia, and Africa. It began like the part-time Greek army, with farmers returning to their fields after a quick summer campaign. Then it changed into a professional organization with long terms of service far from home. The Roman general and seven-time consul Marius is considered responsible for the change of the Roman army into its professional form. He gave the poorest classes in Rome the opportunity to be career military, gave land to veterans, and changed the composition of the legion.

Recruitment of Soldiers for the Roman Army

The Roman army changed over time. The consuls had the power to recruit troops, but in the last years of the Republic, provincial governors were replacing troops without the approval of the consuls. This led to legionaries loyal to their generals rather than Rome. Before Marius, recruitment was limited to citizens enrolled in the top 5 Roman classes. By the end of the Social War (87 BCE) most of the free men in Italy were entitled to enlist and by the reign of Caracalla or Marcus Aurelius, it was extended to the entire Roman world. From Marius on there were between 5,000 and 6,200 in the legions.

Legion Under Augustus

The Roman army under Augustus consisted of 25 legions (according to Tacitus). Each legion consisted of about 6,000 men and a large number of auxiliaries. Augustus increased the time of service from six to 20 years for legionaries. Auxiliaries (non-citizen natives) enlisted for 25 years. A legatus, supported by six military tribunes, led a legion, composed of 10 cohorts. 6 centuries made a cohort. By the time of Augustus, a century had 80 men. The leader of the century was the centurion. The senior centurion was called the primus pilus. There were also about 300 cavalry attached to a legion.

Contubernium of Soldiers in the Roman Army

There was one leather sleeping tent to cover a group of eight legionaries. This smallest military group was referred to as a contubernium and the eight men were contubernales. Each contubernium had a mule to carry the tent and two support troops. Ten such groups made up a century. Every soldier carried two stakes and digging tools so they could set up camp each night. There would also be enslaved people associated with each cohort. Military historian Jonathan Roth estimated there were two calones or enslaved people associated with each contubernium.

"The Size and Organization of the Roman Imperial Legion," by Jonathan Roth; Historia: Zeitschrift für Alte Geschichte, Vol. 43, No. 3 (3rd Qtr., 1994), pp. 346-362

Legion Names

Legions were numbered. Additional names indicated the place where the troops were recruited, and the name gemella or gemina meant the troops came from the merger of two other legions.

Roman Army Punishments

One way to ensure discipline was the system of punishments. These could be corporal (flogging, barley rations instead of wheat), pecuniary, demotion, execution, decimation, and disbandment. Decimation meant one in 10 soldiers in a cohort was killed by the rest of the men in the cohort by clubbing or stoning (bastinado or fustuarium). Disbandment was probably used for mutiny by a legion.

Siege Warfare

The first great siege war was waged by Camillus against the Veii. It lasted so long he instituted pay for the soldiers for the first time. Julius Caesar writes about his army's sieges of towns in Gaul. Roman soldiers built a wall surrounding the people to prevent supplies from getting in or people from getting out. Sometimes Romans were able to cut off the water supply. Romans could use a ramming device to break a hole in the city walls. They also used catapults to hurl missiles inside.

The Roman Soldier

"De Re Militari", written in the 4th century by Flavius Vegetius Renatus, includes a description of the qualifications of the Roman soldier:

"Let, therefore, the youth who is to be chosen for martial tasks have observant eyes, hold his head up, have a broad chest, muscular shoulders, strong arms, long fingers, not too extended a wait measure, lean hams, and calves and feet not distended with superfluous flesh but hard and knotted with muscles. Whenever you find these marks in the recruit, do not be troubled about his height [Marius had set up 5'10 in Roman measurement as the minimum height]. It is more useful for soldiers to be strong and brave than big."

Roman soldiers had to march at an ordinary pace of 20 Roman miles in five summer hours and at a fast military pace of 24 Roman miles in five summer hours carrying a 70-pound backpack.

The soldier swore an oath of loyalty and implicit obedience to his commander. In war, a soldier who violated or failed to carry out the general's order could be punished by death, even if the action had been advantageous to the army.


  • Polybius (c. 203-120 B.C.) on the Roman Military
  • "Training Soldiers for the Roman Legion," by S. E. Stout. "The Classical Journal", Vol. 16, No. 7. (Apr., 1921), pp. 423-431.
  • Josephus on the Roman Army
  • "The Antiqua Legio of Vegetius," by H. M. D. Parker. "The Classical Quarterly", Vol. 26, No. 3/4. (Jul. - Oct., 1932), pp. 137-149.
  • "Roman Legionary Fortresses and the Cities of Modern Europe," by Thomas H. Watkins. "Military Affairs", Vol. 47, No. 1. (Feb., 1983), pp. 15-25.
  • "Roman Strategy and Tactics from 509 to 202 B. C.", by K. W. Meiklejohn. "Greece & Rome", Vol. 7, No. 21. (May, 1938), pp. 170-178.
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Gill, N.S. "The Roman Army of the Roman Republic." ThoughtCo, Jan. 12, 2021, Gill, N.S. (2021, January 12). The Roman Army of the Roman Republic. Retrieved from Gill, N.S. "The Roman Army of the Roman Republic." ThoughtCo. (accessed June 5, 2023).