The cap of Napoleon Bonaparte, the ruler of the French Empire in the 19th century, was sold for 1,9 million euros at an auction in Paris.
The black beaver fur hat was estimated before the auction at between 600.000 and 800.000 euros, but it reached a much higher price.
The identity of the buyer has not been disclosed.
Historians say that the cap was the trademark of the French military leader and emperor.
By wearing it sideways, he made it recognizable so that Napoleon's officers and soldiers knew that the emperor was also in battle.
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Over the years, he owned about 120 such caps.
He usually had 12 caps in his collection and each one was changed after three years.
And when new ones were made, Napoleon would first give them to the valets to soften them, that is, so that he could then shape and wear them more easily.
However, only 20 are now thought to remain, many of which are in private collections.
The cap was sold along with other Napoleonic items owned by the industrialist who died last year.
But auctioneers say this hat is the real holy grail.
Napoleon wore it so that the ends were parallel to the shoulders - also known as en bataille (in battle) - while most of his officers wore their caps vertically towards their shoulders.
A similar cap, part of a collection owned by the royal family of Monaco, was also sold at auction in 2014 for 1,9 million euros to the owner of South Korean food and agriculture giant Harim.
"People everywhere recognized this cap. When they saw her on the battlefield, they knew Napoleon was there too," says auctioneer Jean-Pierre Ossenat.
"He had it on his head even when he was alone or held it in his hand, and sometimes he deliberately left it on the ground. It was an imperial symbol," he adds.
The auctioneers say that the hat has an unquestionable origin and that it remained during the 19th century in the family of the quartermaster of Napoleon's palace.
The cap, which was put up for sale by the Osenat auction house in Fontainebleau, has the cockade Napoleon attached to it in 1815 when he crossed the Mediterranean Sea, returning from exile on Elba to Antibes, only to briefly return to power.
Other items up for sale include a silver plate looted from Napoleon's carriage after his defeat at Waterloo in 1815 and a wooden suitcase, as well as a razor, silver toothbrush and scissors.
The same cap that Napoleon wore in the Battle of Waterloo (pictured below) was sold five years ago for 280.000 euros.
Napoleon's clothing worn in battle has become a collector's obsession over the years.
The red cloak he wore at the Battle of Waterloo belongs to the British royal family and has been in the Royal Collection since 1837.
Napoleo wore this embroidered ankle-length cloak the night before the French defeat, and after the victory, Allied soldiers, led by the British, looted his carriage.
Napoleon declared himself emperor in 1804 and waged wars with other European powers, conquering much of the continent, before his final defeat in 1815.