An exhibition featuring the intricate designs of imperial architecture of the Qing Dynasty (1644-1911) is on show at the National Library of China. The exhibits, titled the Yangshi Lei archives, are design files kept by the Lei family, who worked on the design, construction and maintenance of buildings for the Qing court for more than 200 years. Their designs can be seen in the Forbidden City, the Altar of Heaven, the Beijing Summer Palace, the Chengde Mountain Palace, and the Eastern and Western Qing Mausoleums. These make up one-fifth of all of China's registered World Heritage Sites. Details of sections, plans, and working drawings are recorded in more than 20,000 documents of the Lei Family archives. Altogether 276 documents were selected for the exhibition, including a blueprint of Wen Hua Dian in the Forbidden City, a water supply plan for Yuanmingyuan, and the first-hand historical data of the construction of the Altar of Heaven. The UN Educational, Scientific and Cultural Organisation (UNESCO) added the Qing Dynasty Yangshi Lei Archives on its "Memory of the World Register" in June this year. Countries with documents on the list can receive help to preserve them and produce digital copies to make them available across cultures and borders. The exhibition is open free to the public from 9:00 a.m. to 4:30 p.m. at the library until Sep. 23.