Accensi

Accensi (Singular: accensus) were light infantry in the armies of the early Roman Republic. They were the poorest men in the legion, and could not afford much equipment. They did not wear armour or carry shields, and their usual position was part of the third battle line. They fought in a loose formation, supporting the heavier troops. They were eventually phased out by the time of Second Punic War.

History and deployment
Accensi appear to have evolved from the old fifth class of the army under the Etruscan kings when it was reformed by Marcus Furius Camillus. The fifth class was made up of the poorest soldiers in the legion who were equipped with slings and perhaps a small shield. They acted as skirmishers, screening their own formations and disrupting the enemy. It is likely that engagements with the Samnites and a crushing defeat at the hands of the Gauls taught the Romans the importance of flexibility and the inadequacy of the phalanx on the rough, hilly ground of central Italy.

Camillan system
In the early Camillan system of organisation of the 3rd and 4th centuries BC, men were sorted into classes according to wealth, the accensi being the poorest. Accensi were armed with slings which they used to hurl stones at enemy formations. They fought as skirmishers, wearing only a tunic and sometimes carrying a small round shield.

In this type of legion, the 900 accensi formed 15 maniples, military units of 60 men each, which were in turn part of 15 ordines, larger units made up of a maniple of triarii, a maniple of rorarii and a maniple of accensi. The accensi stood in the last line of the legion, behind the front line of hastati, the second line of principes, the third of triarii and the fourth of rorarii. In a pitched battle, the leves, javelin armed skirmishers who were attached to maniples of hastati, would form up at the front of the legion and harass the enemy with javelin fire and cover the advance of the hastati, spear armed infantry. If the hastati failed to break the enemy, they would fall back and let the principes, heavier and more experienced infantry, take over. If the principes did not break them, they would retire behind the triarii, who would then engage the enemy in turn — hence the expression rem ad Triarios redisse, "it has come to the triarii" — signalling an act of desperation. The equites, cavalrymen, were used as flankers and to pursue routing enemies. The rorarii, the poorer reserve soldiers, and accensi, the least dependable troops armed with slings, would be used in a support role, providing mass and supporting wavering areas of the line.

Polybian system
By the time of the later Polybian system of the 2nd century BC, accensi had been phased out. Velites, light skirmishers, would now fulfill skirmishing duties and troops that would usually have gone into the accensi would now be excluded from service.