Aerial photo taken on Oct. 3, 2018 shows the Jinshanling Great Wall in Luanping County of Chengde, north China's Hebei Province. China's National Cultural Heritage Administration has vowed to strengthen the protection of the Great Wall, which is more than 21,000 km long. The Great Wall, a UNESCO World Heritage Site, consists of many interconnected walls, some dating back 2,000 years. (Xinhua/Wang Liqun)