Troubled waters: Paintings show Venice in decline

Within three decades of the death of Canaletto in 1768, the assiduous painter of Venetian cityscapes, Venice itself, that great maritime empire of yesteryear, was finally humbled and sacked by a tempestuous, megalomaniacal Corsican called Napoleon Bonaparte.

In 1797, the great bronze horses of San Marco, which had themselves been pillaged from Constantinople by the rampant Venetians during the Fourth Crusade, were dragged back to Paris (along with a great deal more cultural loot) to adorn the newly refurbished capital. The glory that had once been Venice had finally passed, like a breath on the wind. The sometime Queen of the Adriatic, now toothless, would henceforth live the afterlife of a brilliant, powerless spectacle. Robbed of political clout, it would decline into the sweetest place on earth for partying and romancing and dreaming. And, every second summer, for a good deal of art blether too.

And yet as we look from one to another of these painted representations of Venice by Canaletto and his peers and younger rivals, comparing various different treatments of the same scene, we sense – we know – that the catastrophe, the emasculation, has already happened. The Venice of Canaletto, Bernardo Bellotto (his nephew and apprentice), Pietro Bellotto (his other nephew and other apprentice), Guardi, Joli, Marieschi and all the other painters in this show – is already a postcard town, a vacation stop-over for the rich. That is why we have all these paintings in the first place. That is why this taste for vedute – view paintings – had grown up in the first place. These painters were feeding an unstoppable demand which continues to this day. By the 18th century, Venice was already in terminal decline, and already being obliged to pursue another way of making itself of interest to the world of the present. And what better way than to trade on the glories of its past? Canaletto knew this, and being talented, hard-working and opportunistic, he was able to profit by it, enormously.

His Venetian dealer was a man called Joseph Smith. Smith was a man of great influence amongst the English aristocracy who were flocking to Venice – it was one of the unmissable stops on the Grand Tour. In 1748, Smith was appointed British consul. He commissioned a huge range of Venetian scenes from Canaletto – a number of them are in this show. After Smith's death, the consul's collection was bought by George III, and later became absorbed into the National Collections.

Other English aristocrats bought, too – the Duke of Bedford acquired a job lot. His couple of dozen Canaletto vedute still hang in Woburn Abbey. The 3rd Duke of Marlborough was a client. The British couldn't get enough of Canaletto, whatever it was that his scenes said to them about the enduring appeal of pomp and magnificence when written on water, or of a political system which may have seemed curiously sympathetic to the Whigs. Canaletto repaid the tribute. He loved England back. When, in the 1740s, he had grown sick to death of painting Venice over and over again, he decamped to London for about a decade, and prettified and reorganised various grand sights on the banks of the Thames – rather as he had occasionally embellished and prettified and reorganised his Venetian scenes.

We must come clean about this, though. Sometimes – often – we grow sick of staring at Canaletto's representations of Venice. We have seen them too often. They are too much with us. They are too sleek, too well made, too much yearning to evoke and to laud an artificial paradise. We can see that he is doing his best to ring the changes on his chosen theme, that he is seeking out less familiar views, less obvious standpoints, less well-known nooks and crannies of the city, but it is still, when all's said and done, the same fantastic pantomime dame that he is rouging up for another night on the boards.

His manner of painting does change, and change again, of course, as he ages. In youth, his work can look nervously sombre, as if he didn't want to catch himself out being unserious. As he aged, it seemed to get sunnier and stiller – Venice becomes a frieze at which we are all expected to marvel. Later still, the light becomes harder and colder again, the attention to detail more meticulous. He is at his best when he is letting uproariously untidy human life leak in (the more disadvantaged the better), and less interesting when it is just buildings, canal, buildings and the human element is little more than a decorous adjunct to the scene.

The finest painting in this show, popularly known as The Stonemason's Yard, gives us a scene which takes in a stonemason's yard and, across a canal, a church and other grander buildings. In the foreground, a group of rumbustious children are playing; someone is digging; and a nosey-parkerish woman is leaning out from her upstairs window just a little too far for comfort. Various irregular heaps of unworked stone make a marvellous counterpoint to the finished burnish of the church and its campanile across the canal. It stops them looking almost too monumental – as if they might just be pleased with themselves. It reminds us that ecclesiastical pomp always goes hand in hand with someone else's miseries, that the made was once the unmade, that the unkillable poor will forever be at our side, even in Venice.

There is one painter in this show, Francesco Guardi, who painted Venetian scenes a little later than Canaletto, and who, in his inventiveness, verve and sheer sense of style, makes Canaletto look a bit like the drudge that he so often was. Guardi is not so faithful to detail as Canaletto. In fact, he makes the shapes of buildings along the Grand Canal the starting point for clever exercises in style and formal play. He paints agitatedly, fleckily. In one painting, which takes as its focus the Rialto Bridge, the movement of the gondolas and the sweep of the bridge seem to come together in a kind of curving, swinging dance. The shape of the bridge is replicated in the billowing of canvas. He causes buildings to dissolve into near abstraction. He shows their imperfections – the stucco cracks; buildings sag tiredly. His skies are often more sweetly poignant with Romantic colour than Canaletto's. His people seem to have more vivacity than most. He entertains us more. He has more of a tang of the real.

After all, this was a century of decadence. There had never been such partying, such dressing up, such posing. Guardi captures this sense of life lived wildly on the edge of the final catastrophe. It makes his paintings seem more authentic documents than Canaletto's, truer to the times in which they were made. Canaletto wishes to perpetuate frozen moments of monumental grandeur. That is what, in part, must have so appealed to the English miluds, the mistaken view that this sort of thing just went on and on and on, that the sun would never set on the ancestral achievements of great and indomitable families. Not true, of course. All written on stinking water.

'Venice: Canaletto and His Rivals', National Gallery, London (www.nationalgallery.org.uk) to 16 January