The bicorne hat was a trademark of Napoleon, who wore it athwart, the two points aligned with his shoulders.
"Everybody at the time wore that kind of hat one way, but Napoleon wore it the other way so that everybody would recognize his silhouette on the battlefield," said the auction official.
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During the 15 years of his reign at the start of the 19th century, Napoleon went through about 120 hats. Osenat said only around 20 surviving items had been authenticated as belonging to the emperor, most of which are in museums.
The hat went for nearly five times the 400,000 euros it had been expected to fetch at the auction, where about 1,000 other pieces of Napoleon memorabilia from the Monaco collection were sold over three days.
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Five years ago, the same auction house sold a saber that had belonged to Napoleon for 4.8 million euros, Osenat said.
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