By Becky Branford BBC News Online, in Potosi, Bolivia

Rene is already suffering the lung-scarring disease silicosis

Coca leaves are packed so tightly into his left cheek that he has to speak awkwardly with the other side of his mouth.

I glimpse teeth blackened by tobacco and coca as he talks. Both products ward off hunger, allowing the miners to work a full day without having to stop to eat.

"My name is Rene," he says. "I'm the oldest man in this mine. I'm now 57, and I've been working here for 40 years."

Rene and his small band of workmates are among the 8,000 miners who scratch a living from inside the bowels of the Cerro Rico hill in the Bolivian highlands.

The hill, now honeycombed with mines, no longer yields much for the miners - among them an estimated 1,000 children between eight and 12-years-old - who work it today. Despite four decades of backbreaking work, Rene still cannot afford to retire.

But its past is one of almost unimaginable riches.

The hill was largely untouched when Spanish conquistadores stumbled across it in 1544.

I am rich Potosi, Treasure of the world. The king of all mountains, And the envy of all kings Legend on 16th-century Potosi coat of arms

Over the next three centuries, it yielded a river of riches - more than 62,000 metric tonnes (137 million pounds) of silver that provided the Spanish aristocracy with a lifestyle of profligate opulence and, because it was used to pay off many Spanish debts to neighbours, fuelled much of the economic rise of Europe.

Much of the silver even ended up in China - used to pay for England's new addiction to tea.

Potosi, the city which grew up at the foot of the hill, was said to be paved with silver and became a byword for luxury and splendour. At the height of its splendour in the 17th Century, Potosi was one of the largest cities in the world.

But Spain's unquenchable thirst for silver had a terrible human cost. The African and native Indian slaves ordered into the mines are said to have survived, on average, six months.

The cone of Cerro Rico rises above Potosi's cobbled streets

It is estimated as many as eight million men may have died - from mining accidents, lung diseases caused by the mineral dust, and contamination by the mercury used in processing the silver.

These days, there is a wistful, threadbare feel about the cobbled streets of Potosi, where from almost any spot the perfect cone of Cerro Rico rises in the distance. The faded houses have lost the gilded ornamentation they once had. Some have been saved from total collapse with heritage grants from the old colonial master, Spain.

The locals - mainly Quechua-speaking Indians - complain that their rivers have been polluted by the metal factories.

It feels as though the improvement in conditions since the colonial days down the mines can have been only slight. The miners now work in small private co-operatives. They are no longer slaves, but there is little other choice of work in this remote stretch of the Andes.

The miners make offerings to their devil god - in the shape of a white man

The lack of investment means there are few local smelting factories to process the metals extracted from Cerro Rico - these days, low-grade silver and zinc - ready for industrial use. Ironically, the zinc sheets used to roof the basic housing around the mountain are imported from Europe.

In the small cavern at the end of one of the mining tunnels, Rene methodically shovels rock debris into a large rubber container, his cheek still swollen with coca leaves.

In these cramped tunnels, the heat reaches 40C. This makes it too uncomfortable for the miners to wear face masks that might protect their lungs from the air, which is acrid with metallic-tasting dust.

Bitter taste

Prolonged exposure to this dust is what gives the average miner a life expectancy of only 40 years - and why Rene's longevity is hailed by his workmates.

It is hot, dusty, backbreaking work

They contract what they call the mal de mina, the lung disease silicosis.

"After so many years working, I really want to retire," says Rene, as he waits for the rubber basket, now full, to be winched up a shaft.

"I've been diagnosed with 30% silicosis of the lungs. But we only receive the miner's pension from the government when we have 80% or 90% silicosis of the lungs."