Wujing Zongyao
The original copy of the "Wujing Zongyao" was lost during the Jin–Song wars when the invading Jurchens sacked the Northern Song capital of Kaifeng in 1126 AD. Only a few manuscripts survived as a result of its secretive nature. Very few trustees of the government were ever allowed to read it as increased propagation would have increased the chance of it falling into enemy hands. A remaining copy of the "Wujing Zongyao" was remade into a newly published edition in 1231 AD in the Southern Song dynasty. During the Ming Dynasty (1368–1644 AD), another book was published in 1439 AD featuring fragments of the "Wujing Zongyao" of 1231 while omitting some material and combining it with two other books, including a preface by Li Jin. The entire "Wujing Zongyao" was reprinted in 1510 AD and this version is currently the oldest extant copy available. However, the historian Joseph Needham asserts that the 1510 AD edition is the most reliable in its faithfulness to the original version, since it was printed from blocks that were re-carved directly from tracings of the edition made in 1231 AD, rather than recombining fragments of the original with other material.