| Hastati, Cohort, Triarii, Principes, Velites|
Maniple (Latin: manipulus, literally meaning "a handful") was a tactical unit of the Roman legion adopted from the Samnites during the Samnite Wars (343–290 BC). It was also the name of the military insignia carried by such unit.
Maniple members, seen as each other's brothers in arms, were called commanipulares (singular, commanipularis), but without the domestic closeness of the much smaller contubernium.
Maniple (military unit) Wikipedia
The manipular system was adopted around 315 BC, during the Second Samnite War. The rugged terrain of Samnium, where the war was fought, lacked the maneuverability essential to the phalanx formation which the Romans had inherited from the Etruscans. The main battle troops of the Etruscans and Latins of this period comprised Greek-style hoplite phalanxes, inherited from the original Greek phalanx military unit.
After suffering a series of defeats culminating in the surrender of an entire legion 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.
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 manipular legion, 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.
Sources disagree on the numbers involved and in all likelihood they varied considerably but a generally accepted number is approximately 10-20 120-man maniples of hastati, 10-20 120-man maniples of principes, and 10-20 60-man maniples of "triarii", for a total of 5,000-6,000 men. The maniple was thus roughly equivalent to a double century.
No part of drill is more essential in action than for soldiers to keep their ranks with the greatest exactness, without opening or closing too much. Troops too much crowded can never fight as they ought, and only embarrass one another. If their order is too open and loose, they give the enemy an opportunity of penetrating. Whenever this happens and they are attacked in the rear, universal disorder and confusion are inevitable. Recruits should therefore be constantly in the field, drawn up by the roll and formed at first into a single rank. They should learn to dress in a straight line and to keep an equal and just distance between man and man. They must then be ordered to double the rank, which they must perform very quickly, and instantly cover their file leaders. In the next place, they are to double again and form four deep. And then the triangle or, as it is commonly called, the wedge, a disposition found very serviceable in action. They must be taught to form the circle or orb; for well-disciplined troops, after being broken by the enemy, have thrown themselves into this position and have thereby prevented the total rout of the army. These evolutions, often practised in the field of exercise, will be found easy in execution on actual service.