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Battle and marching formations of ancient Romans

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Roman army was one of the most effective armies on the battlefields in history. For much of Rome’s existence, the foundation of the legions was a disciplined heavy-armed infantry, which, thanks to its training and organization, was able to repel virtually any opponent. The implementation of the strategy and skills for quick regrouping was an indispensable factor in the face of e.g. the environment or the numerical superiority of the opponent.

Roman army was effective not only for its professionalism but also for its ability to regenerate after even the toughest disasters (e.g., the battle of Cannae in 216 BCE). The huge population potential, which largely resulted from the conquest of conquered peoples who provided military contingents, allowed them to operate effectively on many fronts simultaneously. Polybius in his work “The Histories” reports that in 225 BCE the Roman Republic was able to mobilize over 700,000 infantry and 70,000 cavalries.


Centurion at the head of legionaries.

Roman army moving towards the battlefield was formed into several columns, which allowed manoeuvrability. Before the main part of the army were reconnaissance troops: cavalry, light infantry and scouts who followed the movements of enemy troops and made sure that there was no ambush. At the head of the army was also a military tribune or other officers who chose a place to build a camp. Legions marched as separate units with their rolling stock.

In the face of battle and closeness to the enemy army, legion movements were more cautious. The Roman command was looking for the best possible area for combat operations or adapted to the situation. To increase morale, religious rituals were carried out to strengthen the spirit of the soldiers and ensure that the gods were on the Romans’ side. Before the clash, manoeuvres and mutual observation of troops took place, which was to allow the best use of the terrain and the weaknesses of the opponent.

It is noteworthy that Roman legionaries remained silent before the clash, listening to orders, which was to give the command better control of the battlefield. Supervision of the discipline of the army was maintained mainly by centurions and optiones, who were their helpers in the centurion. Optio was guarding troops, patrolling his own centurion in the back. Certainly, the behaviour of the legions that stood in front of the enemy must have made a huge impression on the opponent. It had to prove full self-control and professionalism.

Period of the Republic

During the Republic, light troops (most often velites), which were involved in the fight against enemy skirmishers or light cavalry, started to fight first. Often, such an initial clash led to the involvement of the entire army. A great example is the battle of Trebia in 218 BCE when Hannibal’s light ride pulled across the river the entire Roman army of consul Tiberius Sempronius Longus.

Heavily armed infantry of the Republic period was usually formed in three lines (so-called triplex acies), less often when conditions off-road did not allow – two lines (duplex acies, e.g. Caesar’s army under Ruspina in 46 BCE), single formation (acies simplex) or deep quadruple formation ( quadruplex acies). Individual formations were arranged in a kind of “chessboard”, with free space between them so that riding or skirmishers could freely operate there. Ancient historians compare the pre-battle manipulation setting to the quincunx formation – four elements in the four corners of the quadrangle and one in between.

Triple pattern. Setting up the formation before the battle.

The closest enemy was hastati, then principes, and finally triarii. Hastati together with velites (light infantry) were the youngest and least experienced group in the legion. They were recruited from among men aged 17 to 24 who could afford adequate armament. During the battle, principes were only used when the first line was stopped. The third line soldiers – triariiwere the oldest (30 to 46 years old), the most experienced and the best soldiers in the legion. They were a reserve line that was put into combat at critical moments when the other two lines were stopped.

The greatest disadvantage of the then Roman army was certainly the weakness of the cavalry, which in the event of a strong attack was unable to protect the sides and rear of the army. A great example is the Battle of Cannae. It is worth mentioning that the above triple array could also be modified depending on the needs and approach of the commander. Below are various versions of the Rome troops of the Republic period.

Types of formations used during the Roman Republic.

The tactics of fighting the enemy were very well thought out. When the Roman army approached the enemy line, the Velites and missile troops in front of hastati threw their javelins, fired arrows, and fired slingshots at enemy soldiers, then retreated through the gaps between manipulations for triarii troops. It was an important innovation in Roman tactics, because until now the firing troops had to retreat either through their own already-formed troops, which caused confusion in the ranks, or circled the flanks of the Roman army, which, however, required time. Changes in the structure of the legion allowed light-armed men to move to the rear easily and quickly.

When velites had already passed the first line, they moved to the second stage, forming a battle line. At that time, the commander of the back centuria (posterior) at the head of his people moved first to the left and then forward forming a solid line. The same procedure was also used when velites formed behind the first line to protect the sides of the hastati formation.

Triple array. Withdrawal of vellets for the first row.

At this point, the legion presented a solid strong battle line ready to fight. When the opponent approached, hastati charged. When they lost to the enemy, posterior of centuria returned to its previous position, creating loopholes. At that time, tired maniples of hastati withdrew through the gaps for principes. When the first row was hidden behind the second, principes formed, according to the previous procedure, one strong battle line that charged the enemy. The situation repeated itself, when the second line was losing, which was rare, and then the triarii intervened. This situation was described as: “Going to the triarii” (res ad triaros redit). When even triarii did not defeat the enemy army, the system allowed them to safely leave the battlefield of the whole army.

Empire period

Regarding the military formations and military tactics of the Roman Empire, we can only have speculations. We do not have any treaty that would apply to this period, and the preserved accounts of the battles are not very helpful. However, we can assume that the principle of operation of the Roman military machine was similar.

Certainly, during the battle, the Romans formed the army in several lines to provide adequate reserves. It is worth mentioning that, unlike the Republic, we are not talking about hastati, principes and triaria, but about unified and professional departments, which were supported by the auxiliary. The cavalry was mainly constituted of auxiliary units formed by peoples who specialized in horse riding (e.g. Germans or Gauls). Roman legionaries were supported by propelling troops, but no longer had no Velites.

As in the period of the Republic, the main strength of the Roman army was based on heavy infantry, which was to push the opponent. The ride, in turn, was to attack from the flank and hit the enemy forces from behind. As soon as they saw that one of the sections of the front needed support, the command delegated reserves.

How did Roman legionaries fight?

Roman legionaries under fire.

The equipment of the legionaries was tailored to ensure maximum efficiency. Soldiers first threw javelins (pila) to weaken the enemy’s first line. Then they drew their swords (gladii), which were used to stab in the clinch. The shield (scutum) was large enough for a soldier to successfully protect his body and light to be able to operate freely. During continuous workouts, legionaries learned to use weapons to perfection. All activities were to be automated, which transformed the Roman army into a machine.

In addition, in order to dominate the opponent, the Romans used numerous war machines (ballistas, scorpions, catapults) on the battlefields to throw stones or arrows at the opponent. The use of such means lowered the morale of the enemy and raised their own.

Many scientists also believe that stress related to the life-and-death fight meant that most of the soldiers avoided risky and bold moves. Instead, they approached the enemy soldier carefully. There were no fights for exhaustion. Instead, there were short periods of intense, fierce fighting. The first lines of troops often departed from each other for a short distance to regenerate, pull the wounded off, and then rush to the fight again. As the battle progressed, enormous physical and mental stress increased. Strength and willpower required constant support from comrades who could replace them in combat or get hurt. Finally, when a sudden breakdown occurred in one of the units, the slaughter began. The terror caused the soldiers to lose the last of their courage and cold blood, wanting to escape and save their lives. At that time, the key issues were morale, reserves and decisive command that could save the army from a dramatic defeat.

Vegetius in his work Epitoma rei militaris1 devoted a fragment to the escape from the battlefield:

Generals unskilled in war think a victory incomplete unless the enemy are so straightened in their ground or so entirely surrounded by numbers as to have no possibility of escape. But in such situation, where no hopes remain, fear itself will arm an enemy and despair inspires courage. When men find they must inevitably perish, they willingly resolve to die with their comrades and with their arms in their hands. The maxim of Scipio, that a golden bridge should be made for a flying enemy, has much been commended. For when they have free room to escape they think of nothing but how to save themselves by flight, and the confusion becoming general, great numbers are cut to pieces. The pursuers can be in no danger when the vanquished have thrown away their arms for greater haste. In this case the greater the number of the flying army, the greater the slaughter. Numbers are of no signification where troops once thrown into consternation are equally terrified at the sight of the enemy as at their weapons. But on the contrary, men when shut up, although weak and few in number, become a match for the enemy from this very reflection, that they have no resource but in despair.

Vegetius’ battle formations

The followings are the basic battle formations and battle rules that Vegetius mentions.

First formation

The first formation is an oblong square of a large front, of common use both in ancient and modern times, although not thought the best by various judges of the service, because an even and level plain of an extent sufficient to contain its front cannot always be found, and if there should be any irregularity or hollow in the line, it is often pierced in that part. Besides, an enemy superior in number may surround either your right or left-wing, the consequence of which will be dangerous, unless you have a reserve ready to advance and sustain his attack. A general should make use of this disposition only when his forces are better and more numerous than the enemy’s, it being thereby in his power to attack both the flanks and surround them on every side.

Second formation

The second and best disposition is the oblique. For although your army consists of few troops, yet good and advantageously posted, it will greatly contribute to your obtaining the victory, notwithstanding the numbers and bravery of the enemy. It is as follows: as the armies are marching up to the attack, your left wing must be kept back at such a distance from the enemy’s right as to be out of reach of their darts and arrows. Your right wing must advance obliquely upon the enemy’s left, and begin the engagement. And you must endeavor with your best cavalry and infantry to surround the wing with which you are engaged, make it give way and fall upon the enemy in the rear. If they once give ground and the attack is properly seconded, you will undoubtedly gain the victory, while your left wing, which continued at a distance, will remain untouched. An army drawn up in this manner bears some resemblance to the letter A or a mason’s level. If the enemy should be beforehand with you in this evolution, recourse must be had to the supernumerary horse and foot posted as a reserve in the rear, as I mentioned before. They must be ordered to support your left wing. This will enable you to make a vigorous resistance against the artifice of the enemy.

Third formation

The third formation is like the second, but not so good, as it obliges you to begin the attack with your left wing on the enemy’s right. The efforts of soldiers on the left are weak and imperfect from their exposed and defective situation in the line. I will explain this formation more clearly. Although your left wing should be much better than your right, yet it must be reinforced with some of the best horse and foot and ordered to commence the acnon with the enemy’s right in order to disorder and surround it as expeditiously as possible. And the other part of your army, composed of the worst troops, should remain at such a distance from the enemy’s left as not to be annoyed by their darts or in danger of being attacked sword in hand. In this oblique formation care must be taken to prevent the line being penetrated by the wedges of the enemy, and it is to be employed only when the enemy’s right wing is weak and your greatest strength is on your left.

Fourth formation

The fourth formation is this: as your army is marching to the attack in order of battle and you come within four or five hundred paces of the enemy, both your wings must be ordered unexpectedly to quicken their pace and advance with celerity upon them. When they find themselves attacked on both wings at the same time, the sudden surprise may so disconcert them as to give you an easy victory. But although this method, if your troops are very resolute and expert, may ruin the enemy at once, yet it is hazardous. The general who attempts it is obliged to abandon and expose his center and to divide his army into three parts. If the enemy are not routed at the first charge, they have a fair opportunity of attacking the wings which are separated from each other and the center which is destitute of assistance.

Fifth formation

The fifth formation resembles the fourth but with this addition: the light infantry and the archers are formed before the center to cover it from the attempts of the enemy. With this precaution the general may safely follow the above mentioned method and attack the enemy’s left wing with his right, and their right with his left. If he puts them to flight, he gains an immediate victory, and if he fails of success his center is in no danger, being protected by the light infantry and archers.

Sixth formation

The sixth formation is very good and almost like the second. It is used when the general cannot depend either on the number or courage of his troops. If made with judgment, notwithstanding his inferiority, he has often a good chance for victory. As your line approaches the enemy, advance your right wing against their left and begin the attack with your best cavalry and infantry. At the same time keep the rest of the army at a great distance from the enemy’s right, extended in a direct line like a javelin. Thus if you can surround their left and attack it in flank and rear, you must inevitably defeat them. It is impossible for the enemy to draw off reinforcements from their right or from their center to sustain their left in this emergency, since the remaining part of your army is extended and at a great distance from them in the form of the letter L. It is a formation often used in an action on a march.

Seventh formation

The seventh formation owes its advantages to the nature of the ground and will enable you to oppose an enemy with an army inferior both in numbers and goodness, provided one of your flanks can be covered either with an eminence, the sea, a river, a lake, a city, a morass or broken ground inaccessible to the enemy. The rest of the army must be formed, as usual, in a straight line and the unsecured flank must be protected by your light troops and all your cavalry. Sufficiently defended on one side by the nature of the ground and on the other by a double support of cavalry, you may then safely venture on action.

Vegetius points out, however, that:

It is much better to overcome the enemy by famine, surprise or terror than by general actions, for in the latter instance fortune has often a greater share than valor. Those designs are best which the enemy are entirely ignorant of till the moment of execution. Opportunity in war is often more to be depended on than courage.

Basic military commands

Roman legionaries must have known the military commands their commanders shouted. Below are a few of them:

  • repellere equites – command to prepare troops to repel enemy driving. The squad formed into a square, and the soldiers kept pila between shields, forming a phalanx.
  • iacite pila – order to throw pila at the opponent.
  • cuneum formate – an order to adopt an aggressive wedge formation and to break into the opponent’s line.
  • contendite vestra sponte – a command ordering legionaries to take a combat stance and attack each opponent.
  • orbem formate – Legionaries took the formation of a circle with archers in the centre who provided fire support. This tactic was mainly used when a small squad had to oppose an overwhelming enemy.
  • ciringite frontem – command to maintain position.
  • front allargate – command to disperse positions.
  • testudinem formate – command to form testudo.
  • tecombre – command to leave testudo.
  • agmen formate – command to create a square formation.

More military commands of the ancient Romans

Marching patterns

March of legions. Two soldiers, designated as aquilifer (left and middle), lead their legions.

Marching patterns were used only when moving in hazardous conditions. The most popular was the line array, which did not require a lot of space and provided easy control over the entire army and rolling stock (these were often taken by large legions). The linear pattern consisted of the fact that all departments moved in a long column, in which each of them had a specific place and tasks.

The procession was followed by scouts (expolatores) on horseback or pedestrians (or both), followed by riding, consisting mainly of auxiliary units. Later, troops were set up to prepare the way for the main forces to march. Their task was also often to find the right place for the camp and informed the tribune or officer responsible for designating the site camp. Packed animals with troops of soldiers and officers followed, followed by the commander with senior officers and a retinue. Further on, the ride marched, which was set so as to be able to move quickly to any place of the marching column at any time. The ride was followed by the baggage train, Romans’ siege engines, siege equipment and war machines (their number and type depended on the type of campaign), then legion signs and emblems and trumpets were carried. The main forces followed the signs (legionary cohorts in a fixed order), usually six soldiers. Then they moved to roll stock (food, tools, etc.), and finally followed auxiliares, both on horseback and pedestrians who were the rear guard. Major armies were also flanked on both sides.

Less popular, but also used in the march of legions was the so-called square (agmen quadrarum), where the entire army column was divided into four (not necessarily equal) parts. The front was mainly riding and auxilia, rear riding and infantry, and two sides on the right and left-wing also riding and infantry. In the middle of this formation were rolling stocks, rolling stock, military equipment, etc. This arrangement allowed for very efficient and quick manoeuvres with individual formations but required very efficient organization. The square also allowed for almost immediate combat formation, used mainly in enemy territory in a situation of constant threat; and protection of the legion’s possessions.

Along with Marius’s reforms (end of the 2nd century BCE), there was a significant reduction in rolling stock, as legionaries had to carry their belongings on their backs. It has been accepted to define them with time as “Marius’ mules“. This change allowed to significantly improve logistics, flexibility and operation of legions during war campaigns.

  1. Flavius Vegetius created in the 4th century CE his main work Epitoma rei militaris, which is the only surviving handbook of Roman military. The song was created to highlight the discipline that prevailed in the past in Roman legions. The author believed that a return to ideals would allow to renew the glory of the Roman weapon in the hard times of the Roman state.
  • Ross Cowan, Rzymska Sztuka Wojenna. Od 109 p.n.e. do 313 n.e., 2010
  • Hans Delbrück, History of the Art of War: Warfare in Antiquity, 1990
  • Adrian Goldsworthy, The Punic Wars
  • Adrian Goldsworthy, The Complete Roman Army
  • Vegetius, Epitoma rei militaris

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