A coded letter sent by French emperor Napoleon boasting that his multinational forces would blow up Moscow's Kremlin has sold at auction for 187,500 euros ($A235,000) – 10 times the estimate.
A Paris museum, the Museum of Letters and Manuscripts, secured the October 20, 1812, document with elegantly calligraphic ciphers.
The price, which includes fees, far outstripped the estimate of 15,000 euros, 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 the US, Britain, Japan and Russia, among other countries. 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 on Sunday. A 310-page manuscript for the Essay on Countryside Fortification, which Napoleon wrote in 1818-19 while exiled on the remote island of St Helena, was also bought by the Paris museum - for 375,000 euros, including fees.
Gerard Lheritier, director of the Paris museum, said it already has at least 1500 letters, manuscripts or other writings linked to Napoleon. It recently acquired one from Japan that Napoleon had written to the Empress Josephine; it fetched 600,000-700,000 euros, he said.