A ring thought to belong to France's most famous historical martyr, Joan of Arc, was unveiled on Sunday, March 20 at a theme park, even as historians remained sceptical about its authenticity, AFP reports.

The Puy du Fou historical theme park in the western Vendee region spent 376,833 euros ($425,000) to buy the ring, which is thought to have been in Britain for almost six centuries, at a controversial auction last month in London.

The gold-plated silver ring was dated to the 15th century by an Oxford laboratory, but the trove of historical documents that came with it have yet to prove it belonged to the famous French martyr.

"They are only at the start of the exploration. It's a lot of work but a beautiful adventure," said expert Vanessa Soupault, who observed the ring recently and confirmed traces of gold were visible under the surface.

The bulky piece of jewellery features three engraved crosses and the inscription "JHS-MAR", signifying "Jesus-Maria".

That fits a description recorded at Joan of Arc's trial in 1431, where she told the court the ring had been given by her parents.

Puy du Fou says the ring was probably enlarged and modified at some point in the last 200 years.

Joan of Arc, who fought against the English occupation of France during the Hundred Years War, was burned alive at the stake but became a symbol of French resistance and was later made a saint by the Catholic Church.