Dream of the Red Chamber written in Mongolian. [Photo provided to China Daily]

And Water Margin, Journey to the West, and Dream of the Red Chamber-three classic ancient Chinese novels-written in Mongolian, shows close connection and frequent cultural communication among different ethnic groups, Rao from the national library notes.

In China, "ancient books" are usually defined as those published before 1912, the end of Chinese monarchy. However, for books in non-Han languages, the time span could also be expanded to before 1949.

Some precious books in foreign languages are also included in the directory. A highlight is a copy of the first volume of Das Kapital by Karl Marx, which was printed in Hamburg in 1867.

Recent surveys of ancient books also led to key discoveries among collections of museums and libraries.

For example, Rao cites that, during reign of Qianlong (1736-95) of the Qing Dynasty (1644-1911), the emperor ordered a rubbing replica of the Confucian classics, which was carved on the stone stele in the Guozijian (the imperial college) in Beijing. The rubbing was bestowed to the Confucius' Family Mansion in Qufu, Shandong province, in 1796.