By Joe Boyle BBC News Online

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Why do 1.2 million people flock to the Italian city of Florence every year to look at an enormous statue of a naked man?

On its 500th anniversary, Michelangelo's David is as popular now as it was in 1504.

The appeal is partly sheer size - standing five metres high, the sculpture is as tall as a double-decker bus.

Worked from an enormous block of marble, it weighs in at a staggering six tonnes.

Even to the untrained eye, the dimensions are overwhelming.

No wonder, then, that experts discovered signs of stress in David's ankles last year.

Superintendent of city museums Antonio Paolucci explains: "He's a good looking guy with fragile ankles because when Michelangelo worked his marble he lightened the lower part a bit too much."

But size is not all that matters.

It was very much a symbol of Republican ideals Professor Jane Everson Royal Holloway College

The statue represents one of the greatest achievements of arguably the world's greatest artist.

"Part of the appeal is that he actually managed to finish the whole thing. Michelangelo was famous for not finishing things," says Hugo Chapman, curator of Italian drawings at London's British Museum.

David also put Michelangelo firmly in the A-list of Renaissance artists.

The block of Tuscan marble used for the statue had confounded great sculptors decades before Michelangelo even picked up his chisel.

During the 1460s sculptors had been unable to cope with the size of the block because it was too big.

"At the beginning of the 16th century the idea was resurrected and the young Michelangelo sensed an opportunity," Hugo Chapman says.

He managed to carve the whole statue in less than two years.

Given that he was an artist in his mid-20s with few high-profile pieces in his portfolio, this was a major step.

But not everyone appreciated David's beauty.

Stone-throwing

On its way to be installed outside the Florentine seat of government in 1504, the statue was pelted with stones by local citizens.

Some experts say the attack was politically motivated.

The people were angered at what they saw as a symbol of the Florence republic as opposed to the reign of the exiled Medici family.

The restoration work sparked an 11-year-long argument

Other experts believe the stone-throwing was youthful thuggery.

Either way, the statue survived unscathed and became an iconic symbol of Florence.

"It was created at a time when there was a lot of tension in Florence between the Medici family and the Republicans," says Jane Everson, professor of Italian literature at Royal Holloway College in London.

"It was very much a symbol of Republican ideals because it is the image of the small David standing against Goliath," she adds.

But that is not the end of David's story.

Dirty

A potted history reveals damage to the statue during riots in 1527, when David lost the lower half of his left arm in a riot.

And in 1810 the statue was covered with a protective wax and in 1843 an attempt to remove the wax with hydrochloric acid also stripped away some of the original surface.

David was moved to his current home, the Galleria dell Accademia, in Florence in 1873 for his own protection.

But in 1991 an Italian painter launched a hammer attack on the statue, smashing off a toe.

And in the mid-1990s the suggestion that perhaps David was a little bit dirty and could do with a clean engulfed the art restoration community in a bitter 11-year row.

In 2003 the decision was made to clean the statue using distilled water.

Critics howled that the method could seriously damage the masterpiece.

But in May this year the new-look, cleaner David was unveiled to the Italian public, apparently unharmed by his overdue spring clean.

On Wednesday Florence will kick off nine months of festivities for David's birthday.

Concerts, fireworks, symposiums, exhibitions and of course official David 500 T-shirts will mark the occasion.

After half a millennium of washing, stone-throwing and hammering, David's birthday party is definitely a well-earned celebration.