Nature, time, neglect and millions of footsteps have taken their toll on the Great Wall of China leaving much of it crumbling, but repairing it can be painstaking -- and controversial -- work. After public outcry when a 700-year-old section of the monument was 'fixed' by covering it with cement -- authorities insisted on more authentic restoration using traditional methods: so now labourers, aided by mules, use reclaimed stones and mortar.