ART / A tale of two cities: Andrew Graham-Dixon reveals a visionary blend of the English and the Italianate in 'Canaletto and England'

In 1746 Antonio Canaletto came to London from Venice and many of the pictures he painted during the nine years he spent in the capital suggest an artist uneasily acclimatising himself to new surroundings. London Seen Through an Arch of Westminster Bridge, one of the most instantly memorable pictures in 'Canaletto and England', at the Gas Hall in Birmingham, is a case in point: a painting of one city (London) so suffused with memories of another (Venice) that it represents neither, but rather a fantastical hybrid of the two. The result is deeply ambiguous, stranding anyone who looks at the picture in a place, neither entirely Italian nor entirely English, that seems suspended between fantasy and reality.

The great curving arch of a bridge frames the prospect of a busy metropolitan river alive with commercial activity. The right- hand river bank is dominated by a single landmark, the vast proud dome of a great church towering over the other buildings. But where are you, exactly? The bridge is said to be Westminster Bridge but it could be the Rialto; the river is the Thames but it could be the Grand Canal; the church is Wren's St Paul's but it could be Palladio's San Giorgio Maggiore. The sense of double- take even extends to the blue, blue sky, which looks as if it has been imported from Italy to England for the day.

Canaletto's father was a stage scenery painter and Canaletto would always treat topography with a certain degree of theatrical licence. He saw buildings as stage flats and often rearranged them at will, moving churches this way and that, modifying skylines and relocating monuments to serve his own purposes.

Owen McSwiney, the theatrical impresario and alcoholic who acted as an intermediary between Canaletto and his English patrons, was wrong when he said that 'Canaletto's excellence lyes (sic) in painting things which fall immediately under his eye.' Canaletto's excellence was more subtle and more mobile than that. He was not a great painter of reality, but a painter who made up his own world. Canaletto constantly flaunts the fact in his paintings, and nowhere more consistently, perhaps, than in his handling of the human figure. The diminutive people who inhabit his civic mise-en-scenes, whether English or Italian, are treated with wonderful cursory abstractedness, often just rendered as two or three tiny swipes and dots of colour. They are twinkling ciphers in boats that bob on rippled fields of green, painted with the same freedom that Vermeer (the two painters have more in common than might be thought) brought to art, and carrying the same, muted undertone of insolence: a painter's way of saying, albeit quietly, that he makes up the rules in his own painted world.

Art historians have tended to divide Canaletto's work into topographical paintings (pictures of the real) and capricci (pictures of the imaginary). This has obscured the fact that all his pictures are fantasies of one kind or another. But Canaletto's departures from the truth are also windows on to certain truths about the world which he inhabited, fantasies that reflect on the real.

Canaletto's visionary blend of the English and the Italianate serves as a reminder that mid-Georgian England, the England of Stowe and Stourhead and of architectural neo-Palladianism, liked to see itself through a haze of Italianate metaphor - and a reminder, too, that mid-Georgian London was beginning to formulate a myth of itself as a kind of Venice redivivus, a Venice for modern times. It is well known that the main patrons for Canaletto's views of Venice were English, and had always been, long before he came and worked in this country. But just why the Grand Touring milords of Georgian England should have developed such a fondness for pictures of La Serenissima (the legacy of which is, still, the sheer quantity of Canalettos in England) is a question that has been infrequently addressed.

This show convincingly suggests that Canaletto's Venice exerted such a powerful hold on the English aristocratic imagination in the mid-18th century precisely because it represented a model of their own aspirations. Venice, isolated and embattled centre of a powerful empire, a vital (and extremely wealthy) culture set, like a jewel, in the sea - the parallels, to a Georgian Englishman, were seductively powerful. And it is this ambition, to rebuild England on the model of Venice, that is surely the true subject of Canaletto's London Seen Through an Arch of Westminster Bridge.

The painting's most apparently playful detail, the little bucket that dangles in mid- air from a rope slung down from the bridge in the upper right-hand corner of the picture, is also the key to its meaning. What it says is that this is a bridge (and, by implication, a city; and, by further implication, an entire nation) under construction. What it says is that London, the new Venice, differs from the old one in that it is not a place of crumbling and decay but one of humming activity, with its eye on the present and the future rather than the past. What it says is: Men (Englishmen) At Work. It is an image of Georgian England's fantastic confidence in its own ability to remake eighteenth-century London along Venetian imperial lines.

Canaletto's greatest legacy to the English and to English art may have been a certain idea of Venice (which he did not necessarily invent but to which he certainly painted the most lasting memorials) as an object of emulation. The potency of the idea of Venice as a metaphor for England (which has been largely lost to us now, obscured by the amnesia to which all cultures are subject) would be enhanced still further in the late-18th century, when the Venetian Republic was invaded by the Napoleonic armies. The suppression of the Venetian Republic and the final crushing of Venetian imperial ambitions by the French became, to the English, a fantastically powerful symbol of their own democracy under threat. The Birmingham exhibition contains a wonderfully eccentric painting by William Marlow, one of Canaletto's more intriguing English followers, which makes precisely this point. Painted 50 years after Canaletto had painted London as Venice, Marlow's Capriccio of St Paul's Cathedral on the Grand Canal reverses the trick and paints Venice as the image of London. The political implication is clear: the invasion of Venice is a surrogate invasion of England, so closely have the two places become allied in the English imagination.

Venice in peril had come to equal London in peril, and this may suggest some of the ways in which Turner's great and much later paintings of the Italian city were so subversive. Nearly 100 years after Canaletto came to England, Turner went to Venice and painted the city as a molten chaos of light and almost indeterminate form. Doing so, he took an iconoclast's hammer to the Venice of Canaletto and, almost as if to make the point, included the figure of Canaletto in one of these pictures (The Bridge of Sighs, Doge's Palace and Customs House, Venice: Canaletto Painting) as a barely recognisable blob of a figure daubing an unreadable blob of a canvas.

Painting this picture, Turner not only announced his own apostasy from Canaletto's clear-eyed, poised form of visionariness but also, perhaps, his apostasy from the idea of Venice that Canaletto represented. Canaletto gave the English Venice as an ideal to be aspired to, a great symbol of an embattled but stubbornly empire-building culture. For Turner, however, great painter of flux and fallenness, all empires (all things) are doomed to decay and atrophy.

Turner remade Venice as an emblem of inevitable cultural disintegration and turned the city into a symbol of the fate that awaits all human empires. And he did so at precisely that moment, just a few years before the accession of Queen Victoria, when the British Empire was about to become the most powerful political machine on earth. Painting once-imperial Venice as meltdown, Turner painted his disdain for the very idea of empire. He also, incidentally, predicted the future of Britain.

'Canaletto and England': at the Birmingham Gas Hall until 9 January 1994 (021-235 2834)

(Photograph omitted)