A map due to be unveiled in Beijing and London next week may lend weight to a theory a Chinese admiral discovered America before Christopher Columbus.
The map, which shows North and South America, apparently states that it is a 1763 copy of another map made in 1418.
If true, it could imply Chinese mariners discovered and mapped America decades before Columbus' 1492 arrival.
The map, which is being dated to check it was made in 1763, faces a lot of scepticism from experts.
Chinese characters written beside the map say it was drawn by Mo Yi Tong and copied from a map made in the 16th year of the Emperor Yongle, or 1418.
It clearly shows Africa and Australia.
The British Isles, however, are not marked.
The map was bought for about $500 from a Shanghai dealer in 2001 by a Chinese lawyer and collector, Liu Gang.
According to the Economist magazine, Mr Liu only became aware of the map's potential significance after he read a book by British author Gavin Menzies.
The book, 1421: The Year China discovered the World, made the controversial claim that a Chinese admiral and eunuch, Zheng He, sailed around the world and discovered America on the way.
Zheng He, a Muslim mariner and explorer, is widely thought to have sailed around South East Asia and India, but the claim he visited America is hotly disputed.
The map is now being tested to check the age of its paper and ink, with the results due to be known in February.
Even if it does prove to have been drawn in 1763, sceptics will point out that we still only have the mapmaker's word that he copied if from a 1418 map, rather than from a more recent one.