At the time of the Hsi-hsia invasion, some person or persons unknown chose one of the caves as a hiding-place for thousands of Buddhist sutras and other manuscripts. In the centuries that followed, all memory of this vast storehouse seems to have been lost, but the precious artifacts survived in safety until the 20th century, when they were rediscovered by an appreciating world. Among the manuscripts was perhaps the oldest printed book - actually a scroll - in existence, the Diamond Sutra, dated 868.
At the beginning of the 20th century, an abbot named Wang Yuan-lu came to Dunhuang area, discovered the sand covered stone grottoes, took up residence in one cave and began to clear out the others. Eight hundred and fifty years had elapsed since Hsi-shia had invaded this territory.
In 1900, the secret library (Cave 17) was discovered by Abbot Wang when he was sweeping out sand and dust from a cave (Cave 16). The secret library is a small stone room contained well over 10,000 manuscripts and silk paintings, many of which were Hsuan-tsang's own translations of Buddhist texts, patiently copied and preserved by Buddhist monks. No one knows when or who bricked over and whitewashed the door and painted murals on it.
In march 1907, a British expedition under Sir Aurel Stein arrived at Dunhuang and visited Wang in his cave. Stein took away total of twenty-four cases, heavy with manuscripts, and five boxes of paintings, embroideries and art relics, which all had only cost him 130 pounds.
According to National Library of Peking in 1961, the Diamond Sutra is described as: "The Diamond Sutra, printed in the year 868....is the world's earliest printed book, made of seven strips of paper joined together with an illustration on the first sheet which is cut with great skill." The writer adds: "This famous scroll was stolen over fifty years ago by the Englishman Ssu-t'an-yin [Stein] which causes people to gnash their teeth in bitter hatred." It is currently on display in the British Museum. The scroll, some sixteen feet long, 17 an half feet long and 10 and half inches wide, bears the following inscription: " reverently made for universal free distribution by Wang Jie on behalf of his parents on the fifteenth of the fourth moon of the ninth year of Xian Long (May 11, 868)"
Who and why hid such treasures in the cave after all? It remains a mystery.