The letter, addressed to King Ferdinand and Queen Isabella of Spain and describing the explorer's discoveries in the New World, was one of 16 copies made at the time of the original missive on Columbus's orders.
Stolen from the National Library of Catalonia in Barcelona in 2004 or 2005, the document was handed over late Wednesday to the Spanish ambassador to Washington, US officials said.
The thieves who took the letter had replaced it with a forgery, and the switch was only discovered by experts in 2012 after a tip from an informant that several other copies had been stolen from archives across Europe and replaced with expertly crafted fakes.
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The discovery sparked a seven-year international investigation that reached as far as Paris and Brasilia.
Investigators found that the Barcelona copy had been sold in 2005 by Italian secondhand book dealers for €600,000 ($708,850), and then resold in 2011 for €900,000.
After “long negotiations,” the letter's unidentified owner in Brazil handed it over in 2014 to US authorities, who used experts to establish its authenticity.
In the letter, Columbus tells the Spanish crown everything about his first trip to America, still believing he was in the East Indies.
The text begins with his departure from Puerto de Palos in Spain in August 1492 and ends when he returns to Lisbon in March 1493, seven months later.
“We are truly honored to return this historically important document back to Spain, its rightful owner,” US Attorney David Weiss said at the ceremony to return the document to the Spanish envoy.