I don't understand why the Romans, after being surrounded, didn't simply continue the foreward attack and break though the Carthaginian center. Even after being surrounded they still had a huge numerical advantage on all sides (though I doubt they had been trained to fight under such conditions). From looking at the casualty figures, nearly all of the Carthaginians who died were Gauls/Iberians in the center who were hit in the initial charge. It seems as if the Romans gave up once Hannibal flanked them. The casualities on the Carthaginian side should have been much higher considering they had to fight and kill 70,000 Romans on the field.
I suppose what I'm really asking is what being flanked does to an army's effectiveness(assuming morale is not a factor, which it wasn't in this case).