Once the enemy breaks through your Mansion (fail to defend in a battle) ,you mansion will be on fire.Because of the fire,durability of the wallwill gradually reduce.
You can click on Wall>Defense> Repair to restore the durability
The state of being on fire only last for half an hour, when time is up the fire will automatically extinguish.
Once the durability reaches zero, the Mansion will be forced to randomly teleport within the city.
Once teleported, the durability will be immediately return to the max.