Photo provided by the ancient book protection center of Tibet Autonomous Region shows catalogues of ancient books in Tibetan language collected at Norbulingka, an ancient palace, in Lhasa, capital city of southwest China's Tibet Autonomous Region. Researchers in Tibet Autonomous Region said on March 7, 2018 that they are cataloguing and making digital copies of antique books at Norbulingka, an ancient palace, amid efforts to better preserve the ancient documents. The palace's management office and the regional ancient book protection center jointly launched a survey of old documents in the palace last September. So far, the survey has covered nearly 600 books, with over 400 antique books registered as cultural relics under state protection. Built in the mid-18th century, the palace was added to the UNESCO World Heritage List in 2001 as part of the historic ensemble of Potala Palace. (Xinhua)