One of Napoleon's famous two-pointed hats has been bought by a South Korean collector for $2.57 million at an auction outside Paris, the Osenat auction house said.

The black-felted beaver fur "bicorne" hat was valued at between $430,000 and $570,000, but experts thought it would fetch four or five times that amount.

During his reign as French emperor, from 1804-1814 and again in 1815, Napoleon Bonaparte is said to have worn around 120 of the hats.

Made by French hatmakers Poupard, Napoleon wore them sideways, rather than with points at the front and back, so he could be easily spotted on the battlefield.

Of around 20 hats that still exist, only two or three are in private hands with the rest scattered in museums across the world.

The hat is the most emblematic item of the two-day sale at Fontainebleau on Saturday and Sunday.

Other items sold by French auctioneers Osenat, Binoche and Giquello included a pair of Napoleon's stockings, a scarf and a shirt.

All come from a collection of around 1,000 pieces of Napoleon memorabilia that belonged to Prince Louis II of Monaco (1870-1949), the great-grandfather of current monarch Prince Albert.

Napoleon's Retreat from Moscow (Adolph Northen, 1828-1876). Napoleon wore the two-pointed hats sideways so he could be easily spotted on the battlefield ( Wikipedia Commons )

The hat was acquired by Joseph Giraud, a vet in Napoleon's household, and remained in his family until 1926 when it was sold to Prince Louis' collection.

The collection, which also includes letters and documents relating to Napoleon's reign, military exploits and exile and imprisonment on Saint Helena, is kept at the principality's Napoleon Museum in Monte Carlo.

The Grimaldi family sold a number of pieces, having decided to pursue new museum projects.

"It's a very well-known collection, the provenance of the pieces is incontestable," Thierry Lentz, director of the Napoleon Foundation, said.

The bicorne, meaning two horizontal points, was a variation on the tricorne, or three-pointed hat, which was popular in the 17th century and favoured by American colonists around the time of the American revolution.

Two hundred years after his reign, Napoleon remains a deeply popular historical figure.

The main French association in his memory currently has around 4,000 members.

AFP