Ms Barbari said she was astounded by Facebook’s censorship of the photograph. “Back in the 1950s, during celebrations for school children graduating, they used to cover up Neptune. Maybe Facebook would prefer the statue to be dressed again,” she wrote. She subsequently posted on her Facebook page a message in large letters: “Yes to Neptune, no to censorship.”

She said she was “indignant and irritated”, and asked “How can a work of art, our very own statue of Neptune, be the object of censorship?”

The statue was created in the 1560s by a Flemish sculptor called Jean de Boulogne, nicknamed by the Italians Giambologna. Dominating the piazza, it overlooks a nearby wall that is lined with photographs of partisans who died in the Second World War and a memorial to 84 people who were killed when Fascist terrorists bombed Bologna train station in 1980, in Italy’s worst post-war atrocity.

Facebook, which has 1.4 billion active users, has courted controversy by prohibiting seemingly innocuous images. In January last year it was accused of censoring photos of Copenhagen’s Little Mermaid statue.

A Danish politician said the social media network, founded by Mark Zuckerberg in 2004 in his Harvard dorm room, had blocked her from uploading an image of the statue. Social Democrat MP Mette Gjerskov claimed that Facebook rejected the image, with Danish media reporting the Little Mermaid image was blocked as it contained “too much bare skin or sexual undertones”.