The 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 manipulative (array manipulative) allowed to introduce changes in the combat formation of legionaries. This is attributed to Marcus Camillus, who was considered a defender of Rome against the Gauls. He created an efficient tactical unit consisting of two centuries under the name manipulum. Centuria initially had a hundred infantrymen (hence the name) operating under the leadership of the centurion (centurio). Over time, the centurie principii and hastati were reduced to 60 soldiers, and the centurie triaria to 30 soldiers.
The basis of the Roman army was the legion divided into 30 manipulators. Manipulas were arranged side by side, at intervals, in the form of a chessboard. When one row got into difficulty, he could back through the gaps. In turn, the second row could come forward and start the fight. Both manipulation centuries were commanded by centurions. The front centurion’s commander was called prior and the rear commander posterior.
A triple line, also known as triple array (acies triplex) that was well-matched to Roman standards, was then introduced. Strong and numerous Roman infantry formed a battle line consisting of three ranks:
- first and closest enemy lines – hastati
- second line – principes
- third and last line – triarii, who are often veterans also strong reserve
The Manipul consisted of 120-150 people, six ranks of 20-25 soldiers. Between each manipulation there were gaps in the width of the manipulation’s forehead from the next line. This was to ensure high maneuverability and easy regrouping while maintaining the ability to quickly create a compact line of troops. Before the first heavy-armed array were velites (velites), i.e. light-armed infantry (javelinists, archers). They were set up in a loose, linear formation. On the flanks there was a ride, grouped in 10 squadrons (turmae), protecting the main army from lap. However, riding was not covered by this tactic.
The tactics of fighting the enemy were very well thought out. When the Roman army approached the enemy line, the Velites in front of hastati threw their javelins, fired arrows, and shot slingshot at enemy soldiers, then to retreat through the gaps between manipulations for troops triaria. 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. Then 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.
At this point, the legion presented a solid, strong battle line ready to fight. When the opponent approached hastati they charged. When they lost to the enemy, the posterior centurii returned to its previous position, creating loopholes. At that time, tired manipulations of hastati withdrew through the gaps for principes. When the first row was hidden behind the second, principes formed, according to an earlier procedure, one strong battle line that charged the enemy. The situation repeated itself, when the second line was losing, which was rare, then the triaria intervened. This situation was described as: “The triars have been used” (res ad triaros redit). When even triaria did not defeat the enemy army, the system allowed to safely leave the battlefield of the entire army.
The greatest disadvantage of the then Roman army was certainly the weakness of the cavalry, which in the event of a strong attack could not protect the sides and rear of the army.