Yvonne Roberts: Joan of Arc's skeleton in the closet

It shouldn't happen to a saint. Particularly one who so effectively broke the traditional man-made mould of how a woman was supposed to make her mark. Joan of Arc, the Maid of Orléans, was neither a queen, nor a courtesan, nor a beauty, nor a mother. Instead, she was a "virgin warrior", a leader of men, propelled by her own sense of mission: a patriot for France.

In the space of a year, she led her men in 10 battles, never using a sword herself, and was praised by her generals for her strategic use of artillery. She was wounded twice and became that most feared of female figures: a woman who refuses to conform.

At her trial by the English for witchcraft and heresy in 1431, the judges were as much offended by her liking for men's clothes as they were by her initial refusal to submit to the authority of the church and deny that she had heard saintly voices since the age of 13.

"She is presented as an Amazon, or a knight of old, or a personification of virtue, because the history of individual women and of women's roles has been so thin," wrote Marina Warner in her 1982 book on Joan of Arc.

Even thinner, now, it would appear, if Serhiy Horbenko, a Ukrainian orthopaedic surgeon, has his way. According to him, Joan was no independent woman. Horbenko has hunted through the basilica of Notre-Dame de Cléry near Orléans and discovered the skeleton of a woman who had the well-developed muscles of a soldier. His theory is that this is the remains of Marguerite de Valois, an aristocrat, whom he alleges was the real "Joan of Arc", a puppet of a group of French noblemen, 15th-century masters of spin.

Horbenko's claim is that in the late 1420s the English were threatening the French throne, so a "miracle" was required to boost the monarchy. Marguerite had been trained to fight since childhood. She became "Joan", a simple woman, sent by God to defend France and legitimise the dauphin's claim to the throne.

A second, fake Joan, already accused of witchcraft, appeared at the trial, speaking eloquently, and was subsequently burnt at the stake. "Many people revere Joan of Arc, so I do not take lightly the implications of shattering this myth," says Horbenko.

Taking the myth and doing what he will with it perhaps reveals more about the age-old masculine belief in the limited abilities of women than it does of Dr H's powers of detection. Does he really assume, for instance, that there was only one woman abroad in 15th-century France with the well-developed muscles of a soldier?

History is littered with examples of women, disguised as men, who fought well and bravely at the battle front. Hannah Snell, wounded 12 times, dressed as a man, extracted a bullet from her own groin, for example, at the British naval assault at Pondicherry in 1748, rather than have her trousers taken down and the truth revealed.

How does Horbenko whisk away the evidence of Joan's rural family and country beginnings? How does he explain the counterfeit Joan's ability to impress the judges with the power of her memory during her trial? Perhaps his crusade is not for the truth but to chip away at female iconography, sparse as it is?

Will Horbenko one day reveal that Boudicca was really a Roman stooge - cut down when she was no longer of use? And that Elizabeth I was a man in drag - hence the need to hold fast to her virginal state?

Fact or fable, the French need have no fear. Joan will see off the bone detective. Why? In part because history, until recently, was almost always narrowly defined as a record of the powerful male establishment's take on social and political change. Women and blacks and the working class were off-stage, unimportant.

Part of the enduring magic of Joan of Arc is that she came from this invisible group, the poor and the marginalised. She made history for what she did. But she became a myth, in part, because of who she wasn't - neither rich nor male nor powerful nor aristocratic. Fairytale or not, it will require more than Horbenko's speculations and a skeleton in the closet to take that away.

Joan Smith is away