The manipular system was adopted around 315 BC, during the Second Samnite War. The rugged terrain of Samnium, where the war was fought, was not conducive to the phalanx formation which the Romans had inherited from the Etruscans and Ancient Greeks. The main battle troops of the Etruscans and Latins of this period comprised Greek-style hoplite phalanxes, inherited from the original Greek phalanxmilitary unit. After suffering a series of defeats culminating in the surrender of the entire army without resistance at Caudine Forks the Romans abandoned the phalanx altogether, adopting the more flexible manipular system, famously referred to as "a phalanx with joints". The manipular system was abandoned during the Marian reforms that began in 107 BC.
Structure
Polybius first described the maniple in the mid-second century BC. The manipular legion was organized into four lines, starting at the front: the velites, the hastati, the principes, and the triarii. These were divided by experience, with the younger soldiers at the front lines and the older soldiers near the back. One theory proposed by J. E. Lendon asserts that this order was adapted to the Roman culture of bravery, allowing an initial show of individual heroics among the younger soldiers. At the front of the legion organized into maniples, the velites formed a swarm of soldiers which engaged the enemy at the start of the battle. The second and third echelon generally formed with a one maniple space between each maniple and its neighbours. Retreating troops of the velites could withdraw without disrupting those behind them. Where resistance was strong the hastati would dissolve back through the Roman line and allow the more experienced soldiers in the principes to fight. In turn, the principes could yield to the hardened triarii if necessary. At this point in battle the maniple greatly resembled the phalanx. The hastati were the youngest and least experienced soldiers, and therefore fought on the front-lines. The principes were more experienced soldiers who stood behind the hastati in battle. Finally, the triarii were the veteran soldiers with the most experience. According to Polybius, the most complete and likely the most accurate account, the legion consisted of 10 maniples of 120 hastati, 10 maniples of 120 principesand 10 half strength maniples of triarii containing 60 men each. With 1,200 velites and 300 cavalrymen a legion numbered 4,500 men. However, in times of great need the number might be reinforced up to 5,000.
