By Vincent Dowd
BBC News, Washington
A map has gone on display in the US that contains the first known use of the word "America".
The map is the first to show the full Western hemisphere
The map is thought to have been drawn exactly 500 years ago by a monk in the present-day French region of Lorraine.
The map, which has just gone on permanent display for the first time, was bought by America's Library of Congress four years ago.
It was produced in 1507 in the town of Saint Die by the German monk Martin Waldseemueller.
His was the first map to show a full and separate western hemisphere and in some regards it remains fairly accurate.
One of the main sources for his new work was the knowledge brought to Europe by the Italian explorer Amerigo Vespucci.
The word America - said by many scholars to be derived from the explorer's name - appears however not where the modern US is but where Brazil now is.
That was the region Vespucci had begun to explore.
Nonetheless, the US felt it worth $10m (£4.9m) to acquire the map - which is more than two metres (6ft 6in) wide - from its home in Germany, where it remained for centuries in a remarkably unblemished state.
Dr John Hebert of the Library of Congress says at least one great mystery remains.
No one can explain why only a few years later the same cartographers drew another map of the same area but "America" is not marked.
"After the 1507 map appears, Waldseemueller creates additional materials - in 1516 a map called the Carta Marina, a nautical chart," said Dr Hebert.
"America has been removed from those pieces.
"Waldseemueller never seems to use the name 'America' again in any of his research."
For whatever reason, the map-makers had replaced the word America with a term which both thrilled and terrified explorers of the 16th Century.
It had become "terra incognita" - unknown land.