But the social media giant objected to the image, which shows a naked Neptune – Nettuno in Italian – holding a large trident. “I wanted to promote my page but it seems that for Facebook the statue is a sexually explicit image that shows off too much flesh. Really, Neptune? This is crazy!” Ms Barbari said.

In a statement, Facebook told her: “The use of the image was not approved because it violates Facebook’s guide lines on advertising.

“It presents an image with content that is explicitly sexual and which shows to an excessive degree the body, concentrating unnecessarily on body parts.

“The use of images or video of nude bodies or plunging necklines is not allowed, even if the use is for artistic or educational reasons.”

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”.

And in November, the social network site was forced to back down after censoring a birthday photo of former fireman in Sweden whose face was seriously disfigured in a blaze as a young man.

Facebook twice removed a picture of Lasse (Lars) Gustavson which his friend Bjorn Lindeblad posted up to celebrate his 60th birthday.

In 2015, Facebook published a rule book telling users the type of content they are not allowed to post, including images of genitals and bare buttocks. The company said it restricts nudity because “some audiences within our global community may be sensitive to this type of content”.

It said images of female nipples were forbidden unless a woman’s breasts were “actively engaged in breastfeeding” or where the image showed “breasts with post-mastectomy scarring”.