A Paris museum, the Museum of Letters and Manuscripts, was finalizing its purchase of the Oct. 20, 1812, document with elegantly calligraphic ciphers.
The sale price, which includes fees, far outstripped the pre-sale estimate of €15,000 ($19,500), according to Fontainebleau Auction House south of Paris.
Experts say the letter is unique, written in a numeric code that Napoleon often used to throw off would-be interceptors - notably when he was conveying battle plans. The letter's content also revealed the strains on Napoleon of his calamitous Russian invasion.
"At three o'clock in the morning, on the 22nd I am going to blow up the Kremlin," the letter said, laying out his route of retreat and urging his minions to send rations to the towns to the west. "My cavalry is in tatters, many horses are dying."
Napoleon's prolific correspondence has drawn aficionados from around the world in places like the U.S., Britain, Japan and Russia. Interest appears to be rising as museums like the Museum of Letters and Manuscripts prepare to mark the bicentennial of Napoleon's final defeat at Waterloo in 1815.
The Kremlin letter was but one piece in the vast auction Sunday. A 310-page manuscript for the "Essay on countryside fortification," which Napoleon wrote while exiled on the remote island of Saint Helena in 1818-1919, was also bought by the Paris museum - for €375,000 ($487,000), including fees.
Gerard Lheritier, director of the Paris museum, said it already has at least 1,500 letters, manuscripts or other writings linked to Napoleon Bonaparte. It recently acquired one from Japan that Napoleon had written to the Empress Josephine; it fetched €600,000-€700,000, he said.
"We have many letters that are much more important" than the Kremlin one, Lheritier said by phone. He was unfazed that the price was far above the presale estimate, and speculated that the letter could have fetched €250,000 ($325,000). "This is a nice letter because it's in code, and he's going to blow up the Kremlin - so it's appealing," he said.
Vladimir Hofmann, a French artist of Russian descent who with his brother Andre also bid Sunday, said they'd wanted to purchase the letter for Russia's famed Hermitage museum.
"Why? You know, it's a question of perhaps nostalgia, perhaps patriotism, to return the thing - very important for Russia and for Russian people - to them," Vladimir Hofmann said.
Referring to such Russian interest in the letter, Lheritier said with a chuckle: "I prefer that it stays in France."