The ballroom has been graced by aristocrats, intellectuals, artists and millionaires. The beams on the ceiling date from the early 17th century. And the windows look out over one of the most exquisite squares in central Paris.

But the current occupants of the mansion at 1b, Place de Vosges have little in common with its illustrious history.

“My father was a shopkeeper in the Pyrenees and my mother a Yugoslav gypsy,” said Stéphane Roques. He is among 32 activists who have transformed the 403-year-old historic monument into what is being described as the world’s most prestigious squat.

Their aim is twofold: to provide themselves with a roof in a city where rents are prohibitive for students and ordinary workers, and to attract attention to the thousands of empty premises in the capital.

Mr Roques said that members of his group, Jeudi Noir (Black Thursday), squatted the 1,300 sq m building in October after noticing that it appeared to be vacant. They shoved open a rickety back door and found themselves in surroundings more familiar to the nobility.

Marquise de Sévigne, the French aristocrat famous for the wit and style of her letters, was born there in 1626. Paris Singer, a descendant of the American sowing machine dynasty, rented the house at the turn of the 20th century. Isadora Duncan, the dancer who was his mistress, lived there with him.

The mansion, in the Marais district, is valued at up to €20 million (£18 million) and its red brick and stone front is in harmony with the rest of the exclusive Place des Vosges, which was built by King Henry IV and is thought to be Europe’s oldest planned residential square.

But behind the façade, the squatters — a highly educated group including architects, journalists, a violinist and students of France’s best universities — discovered chaos and unfinished renovation work.

Wires were sticking out of unpainted walls. Dusty plaster boards had been left next to an ancient fireplace. The back stairs wound up to a gloomy, unlit landing. “The building had been abandoned and we think that when a building is empty, the homeless have a moral right to stay in it,” Mr Roques said.

The mansion belongs to Béatrice Cottin, an 87-year-old spinster, whose father was the founder of the Banque Française du Commerce Extérieure (French Bank of Foreign Commerce).

Although she lives in a retirement home, her lawyers say she considers the house as her main residence — a claim contested by Mr Roques, who says the dilapidation proves it has not been occupied for decades.

He says that she began a vast programme of building work to turn the mansion into flats and a foundation for oriental languages, but never completed her project.

The arguments were voiced this week in a Paris court, where Miss Cottin’s trustees called for the squatters to be evicted and ordered to pay damages which could come to several hundred thousand euros. Judgment will be given on January 18.

Mr Roques, who works as a translator, will be in debt for the foreseeable future if Jeudi Noir loses the court case, but even then the time that he has spent in the squat will have been memorable.

“It is no doubt the first and last time in my life that I am able to live in the Place de Vosges,” he said.

It has also significantly raised the profile of the campaign by Jeudi Noir — so called because Thursday is the day of publication of France’s main classified housing advertisement weekly — for a law authorising the requisition of empty buildings. Estimates of the number of vacant premises in Paris vary between 21,000 and 136,000.

Some commentators, however, say that empty buildings are so common because there are already too many laws. Tenants in France, for example, are protected from eviction during winter, meaning that it can be easier and cheaper for landlords to leave a building empty than to rent it out.

No place like home

• In 2009 six squatters aged between 24 and 34 moved into the former Mexican Embassy and Tanzania High Commission in Mayfair. All artists, the squatters invited the public in to view the two mansions, worth an estimated £30 million

• Squatters in Warrawee, Australia, happily moved into a couple’s unfinished $5 million mansion in 1990. The completion of the house, which was fashioned in the style of Gone with the Wind, had been put on hold after the owners’ business collapsed

• Almost 100 squatters lost a legal battle in 2000 aiming to win ownership of a £6 million Victorian block, overlooking Lord’s cricket ground, which Lambeth council had forgotten it owned. Six flats in the block were awarded to squatters, who the judge ruled had proved their claims

• In 2003 two businessmen occupied the penthouse suite of Cape Town’s luxury Strand Beach hotel, running up a £22,500 bill and ordering up to seven seafood platters a night. They were finally evicted by the courts Source: Times database

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