The Free for All Fight

Formations existed because they worked. The Greek phalanx, the Roman legion's lines of maniples, medieval shield walls, and pike and shot squares of the sixteenth century all relied on the same principles: soldiers who grouped together could protect one another, project greater force than they could alone, and better maintain battlefield discipline. Formation provided protection against the shock of cavalry charges as well as reassurance to morale that the infantryman was well supported by his fellow soldiers, also a direct reminder of who they would be hurting should they try to flee.

The specifics of those formations varied highly from society to society and from time period to time period. In fact, many details of how ancient warfare was conducted such as at what distance fighting broke out between opposing armies and how exactly different units positioned themselves relative to one another during a battle are often either unknown to us or debated by historians piecing together what they can from sparse sources. That being said, the existence and use of formations like the phalanx on the battlefield and their military effectiveness being predicated on the formation being able to hold together as a cohesive whole is not in doubt^[1].  

Besides boons to battlefield performance, formations, especially in the pre-modern period, could also take on social hierarchical dimensions as well. Not all soldiers were drawn from the same ranks of society nor were all created equal. Accordingly, a cavalry formation, for instance, might represent the collection of the sons of a state's nobility. A composite army made up of many vassals, mercenaries, or other parties bound to their respective lords, could also derive formations from the personal ties of groups of soldiers to their leaders. For instance, 10th century Viking bands of a few dozen men relying on their chieftains to distribute loot to them after service to a higher authority^[2].