The tunnel grew darker and more claustrophobic, the air harder to breathe. But Daniel Cruz trudged deeper into the bowels of a mountain where thousands of miners toil and countless more are entombed, casualties of a centuries-old lust for silver.

Behind him followed five foreign tourists, outfitted in hard hats with headlamps, here to see an anachronism in the 21st century, medieval mining in Cerro Rico, or Rich Mountain, in Potosi. This cone-shaped peak is at any given moment home to as many as 16,000 shirtless miners, straining in dark caverns with picks, shovels, their own brute strength and little else.

“They have to choose money or life,” said Cruz, who is 27 and started mining here at 17. “When they choose to mine, they are risking their lives.”

This relic from the days of colonial Spain — for Bolivians, a painful symbol of the conquest of their country as well as their most storied mountain for mining — now brings young tourists such as Charles Newman, who on a recent day watched Indian Quechua miners endure 100-degree heat in shafts hundreds of feet below the surface.

“I thought the working conditions were pretty shocking, coming from Europe,” said Newman, a 19-year-old Briton. “It’s quite humbling, actually seeing what they do on a daily basis.”

Tourists, though, may not be able to travel into Rich Mountain much longer, at least if the engineers who have been studying it are right. They say that after 467 years of mining, the mountain is like Swiss cheese, pockmarked throughout and in danger of a catastrophic collapse.

The mountain is still as imposing as it was when Spanish soldiers, their armor clanking, first set eyes upon its red, rocky slopes rising 15,800 feet into the deep blue skies of Bolivia’s southern highlands.

But Nestor Rene Espinoza, a longtime engineer who recently completed the most extensive study of Rich Mountain’s stability, said the evidence of volatility is hard to ignore.

There are 600 mines, he said, and 65 miles of tunnels. Gaping, unmarked shafts drop to oblivion. Runoff turns soil to mush. Part of the mountain’s iconic cone already collapsed into itself.

“We’ve taken all manner of riches from the mountain, but we have not given it the love it now needs,” Espinoza told representatives from Potosi’s mining sector on a recent night. “I’ve said it before: The mountain is ill, and it requires medical care.”

Espinoza’s findings, which were released in August, showed that five large areas of the mountain’s upper levels are at high risk of collapse. The best solution, he said in an interview, is to pump cement into the abandoned shafts, an operation that would cost at least $300 million and take more than a year.

“The mountain has lost the capacity to support itself, so that means we have to intervene,” Espinoza said, noting that because the mountain is under the control of the miners, they are the ones who probably would have to come up with the money.

(Gene Thorp/The Washington Post)

Such an intervention is not going over well in Potosi, where Rich Mountain employs one of every nine inhabitants and is a national symbol for its vital, if tragic, role in Bolivian history.

Mountain is worthy of its name

It all began in 1545, when an Indian shepherd who was forced to spend the night on the mountain started a fire and “saw a white and shining vein – pure silver,” Uruguayan author Eduardo Galeano wrote in the most popular account of the mountain’s history.

The Spanish created a forced-labor system, the mita, putting to work an estimated 3 million Indians over the next 250 years. And what they produced — up to 40,000 tons of silver – provided a steady stream of riches to Spain.

The mountain was so rich that throughout the colonial period, miners could find 50 pounds of silver for every 100 pounds of rock, said Carlos Serrano, a historian and metallurgist here. The miners simply followed the veins, he said, cutting into them and extracting the silver.

“At first, they even worked under open sky,” Serrano said. Then they began to go underground — deeper and deeper and at an ever higher cost, totaling hundreds of thousands of lives over the centuries, victims of cave-ins, beatings by their overlords and exhaustion.

Those familiar with how the mines are run today say the environment is little better. With dozens of deaths each year inside the mountain, miners long ago came up with a brutally fitting moniker for their workplace: The mountain that eats men.

“What’s happening inside the mine is medieval,” Serrano said.

The mines have no lighting, no safety regulations or inspectors, no modern rail cars, and no pumped-in oxygen, leaving miners to inhale a fine, deadly dust.

“With these lungs, at night I can’t even sleep anymore,” said Elogio Tola, who started here at 16 and is now 45, old for this mountain. “When you start to cough now, you cannot stand it like when you’re young.”

Those who work here — including hundreds of boys, some as young as 14 — are under no illusions.

Chewing wads of coca to ward off hunger and exhaustion, some heft huge bags of rocks to the surface on their backs. Smaller, nimbler miners specialize in burrowing into tiny crevices to place dynamite charges. Most spend the workday like their ancestors did: breaking through rock with a hammer and a heavy iron chisel.

For their troubles, most earn a paltry $14 a day, even as a commodities boom is generating far more earnings than in the past.

“For us, there’s nothing,” said Wilber Marino, 41, sweat covering his bare chest, as he took a break in one dark cavern to talk about his life. “It’s for the boss. We work like mules. We work here like slaves.”

The paradox is that since the 1980s, when the state-run mine laid off thousands, the mining here has been carried out by cooperatives controlled by the miners.

But the 35 cooperatives that now mine mostly lead and zinc are unregulated pay no taxes, and critics say they exploit those miners who aren’t lucky or shrewd enough to have become co-op bigwigs.

“They’re called cooperatives, but they’re not really cooperatives,” said Celestino Condori, head of a local group of activists, the Potosi civic committee, which works to modernize the mines. “They are companies with peons.”

‘Another world down here’

On a recent day, tourists from as far away as the United States and Italy got a brief, if exhausting, taste of what it’s like.

They lowered themselves through dark, craggy holes and down wobbly ladders. At one point, they were left panting after helping miners load an old iron rail car with rocks.

“It makes me grateful for what I have,” said Ciaran McGettigan, 24, a recent university graduate from Australia. “It’s just another world down here.”

It’s also a world that’s unlikely to improve soon. But the miners say they’ll never abandon Rich Mountain, no matter how unstable.

“We have to continue to work here,” said Zenon Guzman, 33, who began at age 12. “Where are so many people going to go?”