The director of the Uffizi Galleries also criticised the projection – the Galleries are linked to the other side of the Arno River by the Vasari Corridor, which runs along the top of the Ponte Vecchio.

Eike Schmidt said he was “astounded” and “horrified” that advertising had been projected onto the Renaissance bridge.

“Authorisation was never asked for and we would never have approved such an insult to our cultural heritage,” he said.

The light festival has been held in past years but commercial slogans had never featured. “Last year, for instance, it was dedicated to the 700th anniversary of the death of Dante so lines of his poetry were projected onto buildings,” Prof Schmidt told The Telegraph.

“To use these historic buildings as if they were pages of a tabloid newspaper, with advertisements, is just wrong. These are buildings that people come from all over the world to see. Across the board in Florence, there has been a strong reaction.”

The mayor of Florence said such commercial ads would be banned in future.

Dario Nardella said the council had supported the light festival, called F-Light, for years, and it had “always been appreciated by Florentines as well as tourists.”

“But from next year we will prohibit any sponsorship messages in the projections.”

American Express were asked to comment on the row.  

There have been similar debates in Italy over the years about allowing companies to attach giant billboards to scaffolding when historic buildings are restored, in return for corporations funding the maintenance work.

Huge advertisements, for products ranging from cars to clothing and luxury accessories, have appeared at the entrance to the Vatican in Rome and around the Bridge of Sighs in Venice.

Critics say the billboards are ugly and inappropriate, but cash-strapped cities say it is in the only way of paying for expensive restoration projects.