A copy of a rare 16th century map known as "the birth certificate of America" has been discovered in Germany.
The map, by the famous cartographer Martin Waldseemueller, is credited with being the first to document and name the newly-discovered land of America.
It had been thought that Waldseemueller had only made four copies, but researchers at a Munich university have now discovered a fifth version.
This new map was found in the pages of an unrelated 19th century book.
Sven Kuttner, head of old books at Munich's Ludwig Maximilian University, said: "It seems to be a second edition and this is a unique map. Until now, we have no signs for a further map like this."
German researchers are going to make the map, printed in clear black ink on yellowing paper, available online from 4 July, Independence Day in the US.
A much larger version is already kept in the Library of Congress in Washington DC.
It was given to the United States as a gift by German Chancellor Angela Merkel in 2007 to mark 500 years since the naming of America.
It is thought that Waldseemueller, a prominent 16th century map maker, used information from accounts of early transatlantic voyages to form a picture of America.
The boomerang shape of the continent he drew is barely recognisable as the North and South America landmass we know today.
Waldseemueller named the new land after Italian explorer Amerigo Vespucci, thinking he had been the first to discover it rather than Christopher Columbus.