I WAS 28 when I first visited Venice. But, of course, I had heard all about it before. I had imagined its fairytale palaces and shimmering streets. And often I’d wondered if it even existed: if this city that sparkled across the surfaces of so many canvases, that provided the backdrop to so many books, was simply the outcome of some creative conspiracy.

I’m not sure I knew the answer even after I had been. Venice, to the poetically inclined at least (to the more pragmatic it is pretty much like a blocked sink), is an ethereal place. It arrives in the contemporary imagination via the legacy of the world’s greatest artists.

But its fantastical qualities rest firmly on practical foundations. The fragile façades of its palaces, the lyrical rhythms of arcades, arise less from fairytale visions than from the expediencies of engineering. A city founded on mud shoals amid expanses of water must, of necessity, be light.

Once, Venice was protected by this aquatic environment. But now water presents its most serious threat. This month sees the 40th anniversary of a great flood when the lagoon, swelling almost two metres above average sea level, swilled out the walkways and squares. And we just have to face it: Venice is sinking. It has been doing so — at a rate of about 10cm a century — ever since it was built.

And things are most certainly not getting any better. Sea levels rise ever more rapidly with global warming. Foundations subside. The lagoon is polluted by industrialisation. It fills with sediment. Where, in the first decade of the 20th century, St Mark’s Square flooded fewer than ten times a year, now it is immersed about 60 times annually.

Next week the Venice in Peril Fund, which since the 1966 flood has disbursed millions of pounds for preservation, debates whether enough money has now been spent. Should we keep struggling to preserve this most splendid of cities? Or should it be left to sink gracefully below the tide? The answer seems to me clear.

Venice cannot be saved. The mobile flood barriers that, after long delays and bitter controversies, are at last being built (at a cost of about €4.3 billion) will, if predictions prove right, defend the city for only a few more decades. After that it will surely go the way of all things.

Nothing lasts. Everything that is whole — from wristwatches and washing-machines to the world’s seven wonders — eventually disintegrates. Of the last, none has survived save the Egyptian pyramids. And even they, plundered and eroding, are on their way out. The guardian sphinxes are letting their treasures slip through their paws. The pharaohs may have built their tombs to last for all eternity but even in an arid desert climate, 5,000 years is all their eternity lasts.

So what hope for Venice, surrounded by water — the “universal solvent”. The city is crumbling into its surrounding lagoon as surely as a sugar lump into a tea cup. It faces an invader far more ferocious than barbarian hordes.

Its buildings will die as inevitably as its inhabitants have always done. In 1902 the Campanile di San Marco suddenly collapsed. The tower that stands there today is a 20th-century imitation. Why did this structure decide to call it a day after more than a millennium? Lightning, the clanging of bells, crumbling masonry, were all blamed. But it was the ordinary Venetian citizens who probably had the right answer. “It died of old age,” they explained.

La Serenissima has become a Miss Havisham. She sits, dripping in Renaissance decadence, like some crumbling old dowager in ancestral jewels. Conservationists may try to stop the clock. But time is insatiable. And facelifts are merely a false cover-up. Venice is dying from the inside out. Underpopulated (except by pigeons), chronically polluted and notoriously expensive, it subsides inexorably into theme park status. A city that built its reputation on a hard-nosed mercantile pragmatism has turned to fleecing foreign tourists for a living. It seems more like Disney than a dignified life.

Is there any point in prolonging it? We should let the city go; let her drift slowly towards her stately death. There is a poignant beauty in the process of decay. Decay, after all, is the second half of the story of life. To deny it is as narrow minded as to leave a theatre when the interval comes because you can’t bear to see how the tale turns out. As stones crack and mosses creep, as roots pry into fissures and insects digest, Venice will return to real life.

We have known that she was heading irredeemably towards her doom, at least since 1818, when Lord Byron lamented her fall. Venice, wrote the lyrical Ruskin, perhaps the city’s most devoted lover, “is left for our beholding in the final period of her decline, a ghost upon the sands of the seas, so weak, so quiet, so bereft of all but her loveliness, that we might well doubt, as we watch her faint reflection in the mirror of the lagoon, which was the city and which was the shadow”.

Death can be the only fulfilment of life. Venice should be allowed to sink slowly back into the mirage upon which it has always floated. It should be allowed to subside away into the sediments of memory. It can live there forever in the fairytale land of the imagination. And will it be any the less real for that?

A debate “Enough Money has been spent saving Venice” will be held on June 12 at the Royal Geographical Society. Tickets: 020 7494 3345

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