If you are putting your centuries into columns while attacking you are removing a significant amount of their combat power, because few will actually be able to attack the enemy. Putting them into line increases the number of combatants that will actually engage an enemy force. If you have a force that formed up eight ranks deep, besides throwing pila, most wont be able to participate in the battle. If you have that same force and reform them four ranks deep they will cover more ground and have more bodies in the front ranks, meaning more combat power.
The Roman gaps in their battle lines are what made them easier to maneuver. Maniples and centuries merely needed to stay abreast of one another while marching instead of being perfectly lined up, which is difficult in rough ground or with natural boundaries (creeks, gullies, trees, bushes, fences, etc.). While marching into battle, for control, it would be easiest to either have the maniples in column (prior in lead, posterior behind), and then reformed into maniples on line (prior right, post. left) just before engaging. Or they could move out in maniple on line on the march, already in the rank and file they intend to fight it, and then open the maniples (increase space between rank and file to Polybius' description), which would decrease the size of the gaps between the forces and give individual legionaires the room to throw pila and fight dynamically with sword and shield as the sources describe.
The reality is that formation is dependent on the mission, enemy, terrain, and troops available, among other things.
The Roman gaps in their battle lines are what made them easier to maneuver. Maniples and centuries merely needed to stay abreast of one another while marching instead of being perfectly lined up, which is difficult in rough ground or with natural boundaries (creeks, gullies, trees, bushes, fences, etc.). While marching into battle, for control, it would be easiest to either have the maniples in column (prior in lead, posterior behind), and then reformed into maniples on line (prior right, post. left) just before engaging. Or they could move out in maniple on line on the march, already in the rank and file they intend to fight it, and then open the maniples (increase space between rank and file to Polybius' description), which would decrease the size of the gaps between the forces and give individual legionaires the room to throw pila and fight dynamically with sword and shield as the sources describe.
The reality is that formation is dependent on the mission, enemy, terrain, and troops available, among other things.
