Even no wall or human construction at all. It simply disappeared because it can hide itself very well into any landscape. This stratagem should bear fruit, in theory. But their opponents... They are evil : during a war, they usually put some pieces of fire around the castle until it starts to burn and citizens have some arguments with each other. Usually, a wise man merely suggests his people to resume eating nougat instead of quarreling. Officially, nobody does, because everyone is under jurisdiction of King #9.