Aerial photo taken on April 9, 2019 shows the snowy scenery of the Mutianyu Great Wall in Beijing, capital of China. 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/Bu Xiangdong)