Eleven letters sent by Napoleon Bonaparte, including dispatches from the Kremlin, have gone on sale following the blockbuster auction of the diminutive French emperor's hat for $2.1 million.

Among them is one dated 18 September 1812, in which he arrives in Moscow at the height of his Russian campaign and reports that the city is ablaze amid a scorched-earth policy adopted by the Russian side.

"Today I toured the main quarters. It was a spectacular city; I say 'was' because today more than half has been consumed by fire," the French emperor wrote.

In the missive, on sale for $58,300, he also remarked on the city's inventory of alcohol.

"We have found cellars full of wine and eau de vie (liquor), which will be of great need to us," he wrote. 

Napoleon ordered the largest European military force ever assembled up until then into Russia in 1812 when the French ruler was at the height of his prestige.

But around a million soldiers and civilians died in the course of the invasion.

Nathan Raab, president of the Raab Collection, a Philadelphia-based dealer of historical papers handling the sale, said that "the letter from Moscow is so rare, it's just extraordinary".

"Napoleon is an enormous figure with immense admiration from Americans. He is seen as an emperor with a strong leadership.

"But his legacy is not black or white, it's very gray."

Napoleon later went on to destroy several towers and sections of wall at the Kremlin, at the time both an imperial palace and military fortress.

He had vowed to do so in another letter dated October 20, 1812. 

That note does not feature in the latest sale, having been sold for 187,500 euros at a French auction in 2012.

In another, now on sale for $79,500, Napoleon itemizes the munitions he needed for a final assault on Toulon in southern France after he had been elevated into a leadership position, setting him on course to eventually become emperor.

'Great coincidences'?

"In what may go down as one of the great coincidences in history, he happened to be in the area as the French gathered for the assault on Toulon and was given the command of artillery," according to the Raab Collection. 

"This seemingly insignificant event at the time would make his career, and change the history of Western Europe."

Interest in Napoleon's life has soared as a biopic of the leader's rise to power directed by Ridley Scott is released in cinemas this week. 

Starring Joaquin Phoenix as Napoleon, the film also chronicles his relationship with Empress Josephine played, by Vanessa Kirby.

"He wanted to be heartfelt, but in his letters… he seems like a teenager in love, almost plagiarizing poetry," Phoenix told AFP in Paris recently.

"There's something almost endearing about it — if he wasn't also responsible for the deaths of millions of people," Phoenix added.

"I imagined that he was cold and calculated as a great military strategist. What I was surprised by was the sense of humor and how childlike he was."

A hat belonging to Napoleon sold for a record of nearly two million euros at a French auction on Sunday. 

It broke the previous record for a Napoleonic hat, held by the same auction house, of 1.88 million euros in 2014, shelled out by a South Korean businessman.