Xu Chaoying, a research fellow in the ancient architecture department of the Palace Museum, puts away an ancient treasure box retrieved from the main ridge of Yangxin Dian in the Palace Museum in Beijing on Monday. Yangxin Dian, or the Hall of Mental Cultivation in the Forbidden City, officially started its research protection project Monday, featuring research into the maintenance process itself. According to the museum, the repair covers 7,707 square meters, and the building area is around 2,540 square meters. A total of 13 historic buildings and their affiliated glass doors and wooden screen walls will be repaired. The maintenance project is scheduled to finish in 2020, when the Forbidden City celebrates its 600th anniversary.   Xinhua