The second barrier around the city has been constructed, but it will be very difficult to break it down, because it contains a "coded signal" . This means that the city will not be able to be dispersed, and the only way to get rid of it would be to use a bomb. This is why the city needs a second barrier, because the first one was too weak to resist the attack of the city's enemies. The city needs more time to prepare for a counterattack, but since the city is outside of the anti-magic area, it will have to wait until the next time they need to attack.