Venice: Pure City, By Peter Ackroyd

Venice is a strange candidate for the Ackroyd treatment, particularly when he gives no sign that he knows the city in depth. Conceived on the model of London: The Biography, with its loose, thematic chapters, this is more conventional than that marvellously original work and seems more like a vast quantity of research raked into heaps than the portrait of a living city.

He is brilliant on beginnings, conjuring the early years of the floating city: the watercourse twisting past islets that became the Grand Canal; the palisades among the dunes, the huts of wattle in the marshes. Islands were lost to the sea, centres of power shifted. Gradually the city solidified and Venice was finished, in a way London would never be: "The first stone of the great bridge across the Grand Canal at the Rialto was laid on 31 May 1585. The creation of Venice was complete."

Ackroyd allows himself comparatively few psycho-geographical flourishes: "In Venice there is no true chronological time... There are occasions, indeed, when time seems to be suspended; if you enter a certain courtyard, in a shaft of sunlight, the past rises all around you." If he were writing about London, you feel, he would have named the courtyard. Yet many of his descriptions are evocative, Pater-like, such as this of St Mark's: "It rises from the square like an apparition wreathed in clouds of jasper and porphyry, of opal and of gold," while the interior "is like some great cavern beneath the sea filled with sunken treasure".

In Venice, beautiful surfaces mask rank depths; instability breeds insecurity. "Ambiguity, reflecting the ambiguous state of a city on the water, may be the key," he notes. When historical Venetians appear, individually or in the mass, Ackroyd seems not to like them very much. Their government is repressive; they are childlike, anti-intellectual and not disposed to introspection; they are natural spies and gossips; both melancholic and silly, shallow and unfathomable. This is a digest of what others have said of them, but Ackroyd rarely has anything more positive to add. "Whether the tale reveals more of Venetian mendacity or of Venetian greed is an open question," is a typical pronouncement.

There is a characteristic blurring of timescale throughout. This enables Ackroyd to spread a commentator such as the early 17th-century travel writer Thomas Coryat thinly like butter through the whole book, but also leads him to collapse centuries together and make strange historical judgements. The Venetians outrageously sacked their sister-city Byzantium in 1204, carrying off the famous horses of St Mark's, but to claim, as Ackroyd does, that the fall of the city to the Turks in 1453 is therefore directly Venice's fault is peculiar; 250 years is not the blink of an eye, after all. There are some flights of sonorous nonsense: Venetians, apparently "acquired their love of puppets from the more spectral tradition of Byzantium that emphasises the melancholy aspect of the inanimate doll until human desire gives it breath". Really? Well, I'll eat my tricorne hat.

It seems a bit rich for Ackroyd endlessly to harp on the theme that Venice is dead, a fantasy, a travesty, a shadow, when he makes no attempt to capture the city as a lived experience. Other recent books have done much more to overturn such platitudes: John Berendt's City of Falling Angels and Bidisha's Venetian Masters show outsiders attempting to crack the modern city's complex codes, and Venice is a Fish, by native son Tiziano Scarpa, is full of wit, stories and offbeat observations.

Ackroyd is capricious on Venice's artistic heritage, claiming bizarrely that Venetian portraits show "no trace of the inner life and no attempt at psychological revelation... None of the doges or governors of Venice ever had a 'personal character'." A quick trip to London's National Gallery and a glimpse of the faces of Vincenzo Catena's shrewd Andrea Gritti or Bellini's sublime Leonardo Loredan refutes that notion. Tintoretto, we are told, was "rarely interested in the depiction of individual human beings". His moving portrait of Vincenzo Morosini, peering haggardly out from his velvet and ermine, must be an exception then.

Ackroyd covers an immense amount of ground with verve and elegance, but it seems that Venice, a city of painters, composers and senators rather than necromancers and poets, does not offer him much scope to play to his spooky strengths.