In reference to ancient and medieval battles.

So when you have your unit, did the people slip down between the isles somehow when they were injured or tired? Realistically I'd imagine there'd have to be some sort of a system or the front people would face certain death and flee. I makes sense to me that if they got a moment they could rotate to the back of their line, get some water catch their breath as they line up and move forward again. Please tell me if I'm not explaining myself properly. I'm not talking about the unit of 100 men being in front but the men within that unit 1 man deep.

Obviously sometimes they couldn't, such as if a roman unit was in tetsudo formation.