By the time the first line is driven back the defending army knows where the enemy has chosen to strike and is ready for him on the second line or "line of resistance."  Here the battle is on in all its fury. If here again the enemy advances, there is still a third line of "battle positions."  This is practically the last entrenched position that the defenders have.  If they are driven back from this into the open country beyond, it becomes a serious thing for the retreating army, as many of their big guns will have been lost, and their forces are apt to be more or less disorganized, while the enemy is flushed with the victory he has so far gained.