Carabinieri sealed off one of the grandest houses in the ancient city of Pompeii yesterday after a tall column was found smashed into seven pieces. Officials at the site fear that the destruction is a sign that Mafia gangs are trying to intimidate them.

Pompeii is Italy's most popular tourist destination, drawing 2.5 million visitors every year. And the house of Obellio Firmo is one of its most important. The villa's owner was a leading figure in the city's political life: at his funeral - before the fatal eruption of AD 79 - 10kg of incense was burned in his memory, at vast expense.

The column stood in the villa's garden. No one yet knows exactly how or why it toppled over. The Carabinieri point out that a fierce wind was blowing this week. The House of Obellio Firmo is undergoing restoration, and a high scaffolding stage next to the column was also found on its side: perhaps, they suggest, the wind caught the scaffolding, causing it to smash into the column, destroying it.

But the superintendent of the site, Pietro Giovanni Guzzo, is having none of it. Nor does he believe the damage was caused by vandals. "It's not vandalism," he said. "It's an act of intimidation. It's an attack against a process of transparency and legality. But we won't be stopped, we won't allow them to intimidate us."

Mr Guzzo pointed out that there is a gap in the railings close to the Obellio Firmo house: he suggested that the perpetrators got on to the site that way, clambered on to the scaffolding and pushed the column over.

Both Pompeii and Herculaneum, the other ancient city destroyed in the same eruption, are in an area where the Camorra, the Mafia of Naples, are a constant menace. Naples has seen dozens of vicious attacks and many murders in recent months as rival gangs slug it out for control of the cocaine trade.

Sites like Pompeii and Herculaneum, which earn millions every year from the tourist trade, are hugely tempting for the gangs. They routinely extort protection money from restaurants, hotels and other facilities catering to the visitors outside the ancient city's gates, but they are not beyond trying to get a slice of the action inside.

In 2000 one of Pompeii's most important villas narrowly escaped destruction after a fire was started on the fringe of the ancient city. Arson is a common way for Mafia gangs in Sicily and southern Italy to warn recalcitrant "clients" to cough up. A minister at the time said: "I point my finger at the Camorra."

Then in 2004 a fake bomb was placed in a brothel of the ancient city; the following year, 13 people were arrested on suspicion of trying to force the management of the ruins to buy coffee from a single source, at an extortionate price. Nasty but trivial, one might think - but the price of defiance can be high. During the campaign to elect councillors to modern Pompei's city council in 2004, a candidate called Carlo Cirillo went missing. Two days later his body was found by the roadside, missing its head.