LONDON -- Trafalgar Square is all things to all people. For out-of-towners and tourists, it is where you have your photograph taken with the National Gallery and the church of St. Martin's-in-the-Fields as a backdrop, or of you feeding the pigeons or climbing Sir Edwin Landseer's lions. Four of them stand at the base of Nelson's Column, the central feature of the square. (Smaller replicas guard the doors of Mitsukoshi department stores in Japan.)

For Londoners of the past, the square was where they watched public executions. Now it is a focal point of protest and pilgrimage. When the nation has something to celebrate, revelers dance in the icy fountains. If they are angry, they raise their voices to Nelson atop his column.

At all other times it is a place to be avoided, especially in a car. With roads feeding into it from every direction, the square is a massive, unavoidable roundabout in the neck of central London.

So it was appropriate that the idea for the Fourth Plinth Project, as it is known, was conceived while its instigator, Prue Leith, was stuck in a traffic jam there five years ago. A restaurateur and cookbook author of note, Leith is also vice president of the Royal Society of Arts.

As she glanced idly around the familiar square, her eye alighted upon the northwestern corner where she noticed something odd: an imposing 7-meter-high stone plinth that was as bare as the square was full. Clearly it had been designed to display a sculpture, since the other three plinths each held one -- statues of King George IV and two once famous, now forgotten Victorian soldiers occupied the separate corners of the square.

Why was the fourth plinth empty?

Leith investigated, and discovered a deadlock that had lasted 158 years, caused not by oversight but by the changing nature and perception of public sculpture in Britain, exacerbated by an inability to decide what kind of sculpture should grace a public space as important to the national consciousness, and the further issue of who would pay for it, since the other three statues had been erected by public subscription.

The square was created in memory of the Battle of Trafalgar in 1805, the decisive naval engagement of the Napoleonic Wars where the architect of its success, Admiral Horatio Nelson, had perished on the deck of his flagship, HMS Victory. A grateful nation commissioned the architect Sir Charles Barry to lay out a design for a great square to replace an area of squalid housing and stabling for the king's horses.

This was done between 1829 and 1841, with the first thing erected being a 51-meter-high Corinthian column surmounted by a stone statue of Nelson. In full dress uniform, he faces away from the square and looks down Admiralty Arch and the Mall that leads to Buckingham Palace and beyond. There was no dispute about this, the lions, the fountains or indeed about the king or the two brave soldiers that were added. The plaque beneath Napier's statue states that private soldiers were the most numerous among those who subscribed to its cost.

The problem lay with William IV, the candidate for the fourth corner of the square. William (1765-1837) was king for only seven years and notable only for his long relationship with Irish actress Dorothea Jordan, whose 10 children he fathered. Described as "warm-hearted and well-intentioned but rather eccentric," he left no legitimate male heirs, so his niece Victoria ascended to the throne on his death. He left no provision in his will for a statue to be erected in his honor, either, and since he simply was not popular enough to stimulate public subscriptions, the plinth remained bare.

Over the next century proposals were mooted and shot down, generally on the grounds either of who would pay for the artwork or whether the figure chosen was sufficiently eminent. It was assumed that any statue chosen would be figurative, but no one appeared quite important enough to occupy this key position, and always the question was, who would pay?

Other statues were added -- Jellicoe, Beatty and Cunningham, three admirals from World War I -- but they were set down in the square and not up on the plinth. As time went by, feelings about public art and the type of heroes the public wished to see enshrined also changed. With the exception of Winston Churchill, whose statue stands outside the Houses of Parliament, military and political heroes fell out of favor.

Still, there was no agreement as to who or what should replace them, or in what style. Realistic? Abstract? Somewhere in between?

Or not at all?