One of the prettiest and most historic corners of Rome will soon be sacrificed for a seven-storey underground car park unless Italy's minister of culture orders a dramatic, and costly, change of course.

For the car park’s supporters, it is the way to rid the Tridente, the corner of central Rome defined by the "trident" of streets shooting out from Piazza del Popolo, of the clutter of cars. But its enemies call it "a sacrilegious car park," "a cultural crime", and compare the excavation of the hill in central Rome to the destruction of the Great Buddhas of Bamiyan by the Taliban.

Gianni Alemanno, the new centre-right mayor of Rome, argued against the car park during his election campaign, but work is already under way and if it were cancelled the penalty fees could amount to €40 million. The mayor chairs a meeting of experts on the issue today, but now Culture Minister Sandro Bondi has intervened, saying the hill is a question of national importance and the final word will be his.

It's called the Pincio and towards the end of the Roman Republic Lucullus, the philosopher-general who conquered northern Anatolia and brought cherries to Europe, built a magnificent villa nearby. The property was later grabbed by the libidinous Empress Valeria Messalina, wife of Claudius, who forced its then-owner to commit suicide. Later she herself was assassinated in the villa's gardens, which were transformed into a formal public garden by the 18th century neo-classical architect Valadier.

Pincio remains one of the most beautiful corners of Rome, home to the Villa Medici, where Galileo was imprisoned during his trials, and boasting great views across to St Peter's and beyond. But if plans backed by Mayor Alemanno's predecessor, Walter Veltroni, go ahead, Pincio will became a huge building site as diggers tear the guts out of the hill and replace them with a seven-floor underground car park with spaces for more than 700 vehicles.

The idea is that, after the dust settles, Pincio will look much as it does today. But that view was contested by Giorgio Muratore, a professor of architecture and one of a group of wise men appointed by the mayor of Rome to advise on the project. In an open letter he said, "This project is a monstrosity. That's all there is to it. There are no possible compromises."

One of the most grievous losses, he said, would be that of the panoramic piazza on the hill's flat top, "a large part of which would be redefined merely as the roof" of the car park, with "large ventilator wells, extensive grilles, access stairs and emergency exits". Tourists, instead of "enjoying one of the most enchanting panoramas on the planet," would "walk among air vents fixed on the roof of a gigantic car park".

Environmental groups bitterly oppose the project and Carlo Ripa di Meana, the 79-year-old head of Italia Nostra and former head of Italy's Green party, has threatened to go on hunger strike if it goes ahead.

Opponents were heartened by revelations this week that the hill contains a wealth of ancient Roman remains, "a secret Pompeii," which archaeologists have only begun to explore. Angelo Bottini, special superintendent for Rome's archaeological goods, says, "forty per cent of the area on which the car park is to be built is occupied by archaeological remains”.

Chicco Testa, an environmentalist who backs the car park, says: "We must not be provincial. Anyone who goes around Europe sees that in all the capitals you can find underground car parks in the most central locations: and the pavements are not invaded by cars, as they are here".

But Dr Allan Ceen, an American professor of the history of urban planning who is based in Rome, a campaigner against the car park, pointed out that another enormous undergound car park called the Galoppatoio, a mere 130 metres from the Pincio, is chronically under-used - so much so that part of it has been sold off and is now used as a health centre.

"The Galoppatoio car park is half full - while the streets of the centre are jammed with parked cars - because it costs money to park there," he said. And even if the Pincio car park were to be fully used, he went on, it would not solve the city's parking problem. "When you create a car park in the city centre for 700 cars, you draw 700 more cars into the centre."

But Dr Ceen is pessimistic. "I think it's a foregone conclusion that the car park will go ahead. The idea that this project will allow (the Tridente area) to become a pedestrian area is just an excuse. But the mayor, like his predecessor, will be swayed by the money aspect. They are destroying a very beautiful part of Rome."