VENICE, “a wonderful piece of world . . . rather itself a world” as Ruskin enthused, is a place “from which all ignoble care and petty thoughts are banished”. This summer half the art world will be hustling through the streets of La Serenissima. The Venice Biennale begins in less than a month. Tate Britain has announced details of its Turner and Venice show, which opens in October. But why is it that this city has such power to inspire?

Considered in the cold light of reason, a visit to Venice might sound pretty grim. It is underpopulated (except by pigeons), overvisited, chronically polluted and notoriously expensive. Subsiding inexorably into theme-park status, the city that built its reputation on hard-nosed mercantile pragmatism has turned to fleecing foreign tourists for a living.

But there’s no point in taking a down-to-earth view of Venice. This is a city which seems, quite literally, out of this world. Drifting like a mirage upon the surface of its lagoon, it could almost be set, as one early medieval visitor put it, “between the star Arcturus and the shining Pleiades”.

Later, in the 15th century, a visiting friar wrote that it had “the ocean for a pavement, the straits of the sea for a wall, the sky for a roof”.

Ironically, perhaps, its fantastical qualities rest on practical foundations. The fragile façades of its palaces, the lyrical rhythms of its arcades, rise less from fairytale vision than the expediencies of engineering. Buildings resting upon mud shoals have to be light.

Even decorative splendour had a purpose in the Republic. In a city without fortifications, display came to serve as a sort of defence. Venice, like some exotically plumaged creature, flaunted its riches to protect its territory, proclaiming its power through a show of its wealth. Since it didn’t have the space to double the size of a cathedral or extend a doge’s palace, it would inlay their surfaces and encrust their columns instead.

The craft of the artist became powerfully integral, not just to the physical, but to the political infrastructure. Little wonder that creative skills should have become so prized, that Dürer — who loved the city and visited it twice — should have declared that “here I am a gentleman, at home a parasite”.

When Dürer visited Venice 500 years ago it was at the start of a golden era. From the lyrical Bellini, through the radiant Titian and the atmospheric Giorgione, to the dramatic Tintoretto and the splendid Veronese, the paintings that originated from Renaissance Venice were to include many of the most thrilling pieces in all of Western art history.

The extent to which the character of this painting has been affected by the unique situation of the city has been much discussed. On a practical level, Venice’s status as a trading port would have meant that the artists who worked there would have enjoyed privileged access to the highest-quality minerals, most notably to the rich ultramarines, the warm orpiments and burnished realgars that came from the Near and Middle East.

Whether the famed light of Venice directly affected artistic practice is debatable. But on a bright day no landlocked city could offer such shimmering iridescence as that which is spread sparkling upon the surfaces of the canals. Colour in Venice becomes almost a physical phenomenon. And the often humid, almost palpable, atmosphere tends to soften edges, enveloping forms in an opalescent glimmer. This may well have inspired the city’s painters to take an interest as much in the transient effects of colour, in the sensuous play of light upon painted surfaces, as in classical outlines and immutable shapes.

The splendours of the Venetian aesthetic — widely exported around Europe along the trade routes by which the city thrived — stirred enthusiasms. Rubens, Rembrandt and Van Dyck were all inspired by their visits to the city. And by the time the Grand Tour had became the 18th-century equivalent of today’s gap year, Venice had established itself as a cultural must-see.

Canaletto’s picturesque topographies became so fashionable in Britain that (at least until the war of the Austrian succession in the 1740s curtailed foreign travel) he was almost single-handedly responsible for the entire tourist trade.

Turner, as a young man, would certainly have seen many of Canaletto’s works and, judging by the precision of his early Venetian paintings, from their striking contrasts of light and shade, had clearly absorbed their lessons.

But it was to another, far greater, Venetian master that Turner was to look for more profound inspiration. For a time it seemed that everyone wanted to find “the Venetian secret”. “How to paint like Titian” classes were staged in London to the delight of aspirant amateurs. But although the satrical Gillray caricatured this craze, he exempted Turner from mockery. Turner’s Venice pictures were, at the time, the most popular of his works and still, to the contemporary eye, few will seem more lovely than his later canvases in their ravishing golden hues. One master of colour pays dues to another in these paintings.

Monet’s pictures of Venice focus upon the shimmer of light, the fractured reflections of façades. This painter delighted in the great masters of the Venetian tradition, who in their turn had informed Delacroix, who played so central a role in the evolution of Impressionism.

Venice arrived in the contemporary imagination via the legacy of of the world’s greatest artists. Perhaps, visiting it, it is less the actuality that we seek than myriad cultural reflections made momentarily real. We see in its landscapes a view into the minds and emotions of the artists who have responded to it.

And perhaps, too, like Ruskin, who also described the city as lying “like a ghost upon the sands of the sea, so weak — so quiet — so bereft of all but her loveliness”, we start to wonder which is the city and which is the shadow, which is the fact and which is the fantasy. This may be precisely the source of Venice’s power.

Arriving in the city, the very strangeness immediately disorders expectations. Perceptions and sensitivities become more intensely focused. But, more than that, this is a city which deliberately invites its viewers to experience it as spectacle. And ways of seeing reflect ways of being seen — it seems quite natural that Venetians should have been so famous for making mirrors.

When one looks at Venice, one sees less simple fact than fact as it presents itself in the mirage of the imagination. That is why this city remains so inspiring. It is the place that we go when we want, quite literally, to see how we feel.