Columbus, an Italian from the north-western port city of Genoa, was the first European to land in the New World in 1492.
On February 15th 1493, he penned a letter about his discovery from his Caravel the Niña while making his way back to Europe from the Americas.
Once Columbus arrived in Europe, several copies of letter in various languages were dispatched to different European countries to spread the word.
Only a handful of these copies have survived - one of them in Florence.
The letter was stolen from Florence's Riccardiana library, with the thieves replacing it with a forged copy.
But nobody noticed until 2012.
An investigation was only opened after the National Library in Rome - which also held a version of Columbus' letter - discovered that its document had also at some point been stolen and replaced with an elaborate fake.
In the course of investigations, Italian authorities managed to track down the original letter belonging to the Riccardiana.
The letter was stolen at least 23 years ago as it was bought by a private purchaser at auction in 1992 for €400,000. It was then donated it to the Library of Congress in Washington in 2004.
The letter is today valued at some €1 million.
In a press release the Italian police said they had managed to track down the document thanks to "efficient collaboration with US authorities over the illegal traffic of stolen artefacts".
The letter is of extraordinary historical interest and was unveiled to the Italian press on Wednesday.
U.S Ambassador to Italy, John Phillips, called it "a symbolic event which shows the level of friendship and collaboration between the two countries."