How do the fruits of what is thought to be one of the largest publishing exercises ever undertaken simply vanish? Chances of finding the answer to that question seem to be diminishing with time

It is believed to be the largest paper-based general encyclopedia ever written, presented on 22,937 rolls in 11,095 volumes and using 370 million Chinese characters.

That means if someone had managed to finish reading one volume of The Great Canon of the Yongle Era, or Yongle Dadian, every day it would have taken them a full 30 years to polish off the lot.

Only two copies are known to have existed, the original one commissioned by Zhu Di, known as Emperor Yongle (1360-1424) of the Ming Dynasty (1368-1644) in 1403, and a transcript completed during Emperor Jiajing's reign (1521-66), all handwritten.

Each of the two copies is believed to have taken up about 40 cubic meters - the capacity of about 320 medium-sized cartons, or a small room - yet somehow the original one disappeared.

Only about 400 volumes of the transcript version, less than 4 percent of the total, were collected worldwide. So have the others survived, and if so where could they possibly be?

An exhibition at the National Museum of Classic Books in Beijing since September brings to light anecdotes behind how the masterpiece was put together, preserved, copied and then disappeared, and conjecture about the whereabouts of the original.

Twelve transcript volumes, together with rare historical documents, rubbings, manuscripts, archives and photocopies of the canon published in different periods and collected overseas are on display.

The volumes are from the collection of the National Library of China, which is now home to 224 volumes - more than half of the existing ones. Sixty-two of the 224 volumes are temporarily kept at the Taipei Palace Museum.