Visitors noticed it only recently, though, posting photographs on social media showing a smooth concrete-like surface along the top of a section that was among the most stunning wild stretches of the 21,000km-long structure. Local cultural authorities defended their actions, saying the portion had been in danger of collapse and as unsightly as the use of tightly packed sand may have been, it was a necessary protective measure. The matter has ignited concerns about how vulnerable the relic is to the forces of nature and human activity.

Much of the wall passes through poor, rural counties that lack the finances and resources to adequately protect and preserve it. One-third has already disappeared and of the most substantial part, from the Ming dynasty, just 8 per cent of its 8,852km is still in good condition. Storms over the centuries have caused irreparable damage, but tourist traffic, economic development and a lack of concern and understanding have also had a toll. In Shaanxi (陝西) province, there have been 40 breaches of the structure to build roads and in Hebei(河北), villagers have used the iconic blue and grey bricks to build homes or sold them as souvenirs. Warnings about the wall’s vulnerability have long been voiced; the World Monument Fund made such a call in 2003. A national standard for how repairs should be carried out is necessary. But so, too, is an education campaign promoting the wall’s cultural and historic importance.