One of Napoleon`s famous two-pointed bicorne hats is due to go under the hammer on Sunday at an auction near Paris.
The black beaver felt hat is valued at between 300,000 and 400,000 euros ($375,000-$500,000), but could go for up to two million euros, according to Napoleon memorabilia watchers.
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 hat makers 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 due to be auctioned by French auctioneers Osenat include 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.
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 are selling 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, told AFP.
The bicorne, meaning two horizonal 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 popular historical figure. The main French association in his memory currently has around 4,000 members.