That square solves some of the tough situations when the unit is controlled by the AI and it helps to keep the game interesting right up to the end:

- if a defender unit routs, where does it head to? If it's an attacker, it runs to the edge of the battlemap, but doing the same for the defender units would make sieges easier.

- somekind of last stand must be toughened by having all survivors joined within the same spot and fight to the very end, inflicting as many casualties to the attacker as possible.

- if the survivors keep routing in that last stand spot, they will be killed like sheep and the last stand would have no effect. So the actual way is eliminate the rout as soon as they get into that square.

- by having a time limit for the siege (with the AI as defender), you actually simulate the situation where an army was forced to win the siege before sundown.