ITS'aME'aMARIO!!!! said:lawl, and i have to mention if i haven't already that the wall supports are on the outside of the wall? did the orc build these walls to keep the humans in?
Why didn't the orcs attack till you got there? They see it and think "Oh look, supports on our side, must be our wall" So they don't attack it.
As they're orcs it took them a long time to finally notice "Wait, we didn't build a wall..." and attack it.
Obviously this was mapped like that on purpose.