By Malcolm Billings
BBC Radio 4's Crossing Continents
Malcolm Billings travelled to Naples to find out why people are defying the lessons of the past by living on the slopes of a volcano that could erupt at any time.
Six hundred thousand people live on the slopes of the volcano
Filippo Alaia was only 10-years-old at the time of the last eruption.
"I remember it very well,'' he told me from the old people's centre in San Sebastiano al Vesuvio, one of 18 towns on the slopes of the volcano.
Filippo remembered following the lava flow through the town, and roasting chestnuts on it.
''The older boys,'' he said, "lit their cigarettes on the pools of lava." That was in 1944.
''The war was still going on,'' he recalled. ''American troops helped people to move from the path of the lava and gave us a ride on their trucks.''
That eruption was the last in modern times, and except for an 18th Century church, the town was burnt and crushed by the river of molten rock.
But according to Professor Bill McGuire of University College London, UK, a lava flow is not usually a danger to life.
As he put it: ''You would have to be nailed to the floor to be killed by lava, it moves so slowly.''
The people of San Sebastiano, like the other towns on the mountain side hit by the 1944 eruption, salvaged what they could and started again.
They returned, and re-built their properties using an eight-foot layer of lava as foundation.
About 600,000 people have chosen to live here, ignoring the lessons of 1944, not to mention Pompeii, AD 79.
They have built their homes right up to where the crater rises steeply to the rim some 1,280m above sea level.
The Naples waterfront just across the bay from the volcano
It is not hard to see why people are happy here. The volcanic soil grows wonderful vines and tomatoes, the air is clean, and the views are spectacular.
But the down side is they are living on a massive time bomb, and vulcanologists believe another eruption is overdue.
Ever since 1631, when Vesuvius was almost as fierce as it was in AD 79, there have been regular eruptions.
But now the volcano is unnervingly quiet. There is no hint it is still alive except for some wisps of steam inside the crater.
The activity is monitored. An old stone building sits on a spur of rock halfway up the mountain and has defied the flows of lava for about 150 years.
The old observatory is now a museum. The scientists have a new laboratory in Naples where they monitor the crater's inside temperature, and record every movement.
There are sensors on tripods, waiting to transmit abnormal activity to the scientists in the control room. And out in the countryside there are sensors in deep wells to check water levels.
If the wells dry up - as they did in 1631 - it would indicate that the earth may be fracturing, and an eruption could be imminent.
An evacuation plan is in place should there be an eruption
The authorities are assuming they will get about two weeks' notice if the eruption follows the 1631 pattern.
Women, children, the sick and aged would be moved first, while family heads would stay until the last moment to protect their property.
At some point, the army and the police would arrive to clear everyone out.
The regional government has offered families about 30,000 euros to re-locate out of the danger zone. About 2,500 have applied so far.
There will also be a fund of 10 million euros for people to convert their houses into small tourist hotels.
The theory is that tourists will be able to pack up and leave at a moment's notice if the mountain begins to move.
BBC Radio 4's Crossing Continents
Malcolm Billings reports from the slopes of the volcano on Thursday, 18 March, 2004 at 1100 GMT.
But there is scepticism about the need for an evacuation plan, and distrust of officialdom is widespread.
Vulcanologist Dr Carmen Solana, who is studying the evacuation plan, has found that many people will not leave for fear of looting, and many believe an evacuation might be just an excuse for the authorities to confiscate their houses.
To complicate matters this scepticism is reinforced by scientists at Naples University.
Professor Giuseppe Rolandi, who actually lives on the slopes of the volcano in San Sebastiano, said the mountain showed no signs of erupting, that it might have reached the end of a cycle and could be due for over 100 years of inactivity.
Other experts say they just cannot tell when it will explode or how big the eruption will be.
However, scientists have found out much more about past eruptions.
Pompeii and the smaller town of Herculaneum are still being excavated in an attempt to discover what happened to people almost 2,000 years ago when both towns were wiped out.
Recently discovered skeletons have been analysed and have provided frightening evidence of how some people died.
Professor Andrew Wallace Hadrill, who is directing a conservation project at the site, led me to the Herculaneum port where the remains were found.
On the 25 August AD 79, these people were waiting to escape on boats, as the volcano, just four or five miles away, was exploding, pushing a column of ash and gas 20 miles into the sky.
Professor Hadrill explained that at about midnight the column began to collapse. The ash and the pumice fell back and blanketed the landscape.
People sheltering in waterfront chambers were incinerated
''Then,'' he said, ''a hurricane of gas and ash whooshed down the sides of the mountain. The heat was incredible, about 500 degrees Celsius.
The temperature could be gauged by its effect on the bodies.
Looking at the arches on the ancient quayside under which the refugees were trying to shelter, he explained: "They died instantaneously, their flesh stripped off their bones while the intense heat boiled their brains.''
BBC Radio 4's Crossing Continents was broadcast on Thursday, 18 March, 2004 at 1100 GMT.
The programme was repeated on Monday, 22 March, 2004 at 2030 GMT.