VENICE - The merchants of Venice always had an eye for a ducat to be made in the Rialto, but covering its boutique-lined marble bridge with ads for blue jeans might seem a commercial step too far, even for city built on trade.

Yet with public budgets across Italy struggling to maintain its thousands of historic monuments, that advertising, worth $6.5 million from Diesel jeans tycoon Renzo Rosso, is precisely what Venetian city elders say will keep the Rialto Bridge open across the Grand Canal it has spanned since Shakespeare's day.

"I hope the campaign will not be invasive," Rosso, a local celebrity, said on Friday at a presentation of the plan he is paying for to repair the 400-year-old structure. "Rialto is the most beautiful bridge in the world and it reflects our style."

Aware of carping that accompanied the city's move to tender for commercial sponsors for the project, councillor Alessandro Maggioni said: "Criticism comes with our job. But this city can't wait any longer ... Our monuments are falling to pieces."

Following in the footsteps of a shoe magnate who is paying to fix up Rome's Colosseum, Rosso - popularly known as Italy's "Denim King" - will cover the entire, 5-million-euro cost of restoration of the Rialto Bridge. Work should begin in 2014.

In return, Rosso's company, Only The Brave, may project advertising images onto the bridge, hold publicity events at landmark sites such as St. Mark's Square - and will slap its Diesel brand on Venice's ubiquitous water taxis, the vaporetti.

Events would be artistic and tasteful, said the 57-year-old entrepreneur, who cultivates a rock star look. And the work would only improve a city whose carnival, history, culture and romantic canals draw millions of tourists a year: "Venice is beautiful; Venice is unique," he said. "It's a romantic dream, a love story, and it will be more and more a city of dreams."

DEBT CRISIS

A Renaissance trading empire, Venetian fleets brought home riches from distant shores that allowed its merchant princes to turn the lagoon city into an artistic marvel of the age. But the modern Italian state has hit hard times; deeply in debt and with an economy that has barely grown for a decade, governments in Rome are struggling to find cash to maintain its many treasures.

Locally, Venice is also grappling with the pressure of tourism on fragile, ageing foundations beneath the waterline.

Seeking mercantile help to restore the cracked and stained white marble of the elegantly arched Rialto Bridge is one way of relieving strain on the city coffers, political leaders argue.

In another such example, Diego Della Valle, chairman of luxury shoemaker Tod's, is investing 25 million euros to repair the Colosseum, and wants other business leaders to follow suit.

That project has not been without hitches, however. Earlier this year, Della Valle threatened to pull out after questions over a deal letting him use the 2,000-year-old image in a logo.

There has been scandal over masonry collapsing at Pompeii, the lava-preserved Roman town near Naples; and an offer from a mineral water firm to restore the capital's crumbling but iconic Trevi Fountain led to political uproar, but so far no money.

Venice's heritage has benefited from wealthy business people, including France's Francois Pinault and Italian designer Miuccia Prada, who have restored historic palaces for their own use. But maintaining public monuments remains a difficulty.

For the Rialto Bridge, Venice was not inundated with offers - Rosso's was the only bid at the tender for advertising rights.

Writing by Antonella Ciancio; Editing by Alastair Macdonald