A rare coded letter in which Napoleon Bonaparte vows to blow up the Kremlin is going on the auction block.

"At three o'clock in the morning, on the 22nd I am going to blow up the Kremlin," the famed French general wrote in a letter dated Oct. 20, 1812 and signed "Nap" in his hand.

Written the day after his retreat from Moscow, the letter shows Napoleon at one of his weakest moments before the beginning of a disastrous westward retreat by French forces, according to The Associated Press.

The document, written in Napoleon's infamous numeric code, goes on sale Sunday at France's Fontainebleau Auction House, the AP reported.

It is currently part of a private collection.

"Letters written by Napoleon from Russia are rare," Alain Nicolas, an expert for the auctioneer Ocenat, told AFP. "Many were lost, probably intercepted by the Russians."