User blog comment:Vampires rule/twilight question HELP?!?!?!?!/@comment-121.220.60.142-20121222233618

During the fight, Aro doesn't join in on the actual battle until he becomes infuriated with all the losses of his guard. He goes after Bella and Edward. Bella, at that stage, is already a couple of months old so her newborn strength is already fading. When he provoked the fight by killing Carlisle, Aro managed it because he has probably been trained to fight as well which was why he was managing, but struggling, to fight Bella and Edward at the same time. Aro has had heaps of experience in fighting so it's not his strength but is his skill. I hope this makes more sense to you.