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Reform of the Roman army in the 4th century BCE (the so-called Camillian reform) and the transformation of its structure from a rigid phalanx to a much more flexible manipular (manipular order) allowed for changes in the formation of combat legionaries. This is attributed to Marcus Camillus, who was considered the defender of Rome against the Gauls. He created an efficient tactical unit composed of two centuries called the maniple. Initially, Centuria consisted of one hundred infantrymen (hence the name) operating under the leadership of a centurion (centurio). Over time, the principii and hastati centuries were reduced to 60 soldiers, and the triarii centuries to 30 soldiers.
The basis of the Roman army was the legion divided into 30 maniples. Maniples were arranged next to each other, at intervals, in the form of a chessboard. When one row got into difficulties, it could retreat to the rear through the gaps. In turn, the second row could go forward and start the fight. Both centuries of maniple were commanded by centurions. The commander of the front century was called prior and the back posterior.
The rise of the triple array
Over time, triple line, also known as triple array (acies triplex), was introduced to Roman standards. Strong and numerous Roman infantry formed a battle line consisting of three lines:
- first and closest enemy line – hastati;
- second line – principes;
- third and last line – triarii, being veterans who are also often strong reserve.
The maniple consisted of 120-150 men, 6 ranks of 20-25 soldiers. Between the individual maniples, in each array, there are gaps in the width of the maniple’s forehead from the next line. This was to ensure high manoeuvrability and ease of regrouping while maintaining the ability to quickly create a compact line of troops. Before the first heavy armed formation, there were velites, i.e. light infantry (spearmen, archers). They were arranged in a loose, linear formation. On the flanks there was cavalry grouped in 10 divisions (turmae), protecting the main army from being encircled. However, driving was not included in this tactic.
The tactic of fighting the enemy was very well thought out. As the Roman army approached the enemy line, the Velites in front of the hastati threw their spears, fired arrows and fired slingshots at enemy soldiers, then retreated through the gaps between maniples, behind the triarii. It was an important innovation in Roman tactics because until now the missile units had to withdraw either through their own already formed units, which confused the ranks or around the flanks of the Roman army, which, however, took time. Changes in the structure of the legion allowed light-armed forces to move to the rear easily and quickly.
Once velites had passed beyond the first line, it was moved to the second stage, the formation of the battle line. Then the commander of the rear century (posterior) at the head of his men moved first to the left and then forward, forming one solid line. The same procedure was also followed when velites formed behind the first line to protect the sides of the hastati formation.
At this point, the legion presented a solid, strong battle line ready to engage. As the enemy approached, the hastati charged. When losing to the enemy, the posterior of the century would return to its previous position, creating gaps. Then the tired maniples of hastati retreated through the gaps behind principes. With the first row hidden behind the second, principes formed one strong battle line following an earlier procedure that charged the enemy. The situation was repeated when the second line was losing, which was rare, and then there was a triarii intervention. This situation was described as: “It has come to the Triarii” (res ad triaros redit). When even triarii did not defeat the enemy army, the system allowed the entire army to leave the battlefield safely.
The greatest disadvantage of the Roman army at that time 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.
Patchy front and command
As Plutarch tells us in his biography of Emilius Paulus, there were several partial battles during the battle of Pydna, instead of one massive, massive one. It can be understood in such a way that the front was not uniform and the fighting took place in selected sections. The generals, depending on the course of the situation, could decide to strengthen a given zone or to regroup and strengthen the attack in another sector. It is possible that the idea of such a way of fighting arose during the struggle between Rome and the Samnites in the 4th century BCE in the mountainous area of central Italy.
The effectiveness and flexibility of the Roman army also resulted from the large number of officers who had under their command troops sufficiently numerous to create an advantage and to be able to efficiently control them.
An interesting description of the operation of the Roman army is shown to us by Vegetius:
In the beginning of an engagement, the first and second lines remained immovable on their ground, and the trairii in their usual positions. The light-armed troops, composed as above mentioned, advanced in the front of the line, and attacked the enemy. If they could make them give way, they pursued them; but if they were repulsed by superior bravery or numbers, they retired behind their own heavy armed infantry, which appeared like a wall of iron and renewed the action, at first with their missile weapons, then sword in hand. If they broke the enemy they never pursued them, least they should break their ranks or throw the line into confusion, and lest the enemy, taking advantage of their disorder, should return to the attack and destroy them without difficulty. The pursuit therefore was entirely left to the light-armed troops and the cavalry. By these precautions and dispositions the legion was victorious without danger, or if the contrary happened, was preserved without any considerable loss, for as it is not calculated for pursuit, it is likewise not easily thrown into disorder.
– Wegecjusz, De re militari
