Aerial photo shows a pair of watchtower, or Diaolou, in Zhibo county of Maerkang in Aba Tibetan autonomous prefecture, Sichuan province, Sept 5, 2017. Towering over houses, the 43-meter-high twin towers were built in Qing Dynasty to keep an eye and offer shelter during wars. The cube-shaped stone structure has withstood several earthquakes, including the magnitude-7 earthquake in Jiuzhaigou in August. [Photo/VCG]