Legend has it that the Inca knew about the riches lying beneath the Cerro. According to Uruguayan writer Eduardo Galeano, an Inca named Huayna Capaj led a team of treasure seekers to its summit long before the Spanish arrived. As they began to dig, though, a fearsome voice thundered from the heavens. “This is not for you,” it warned. “God is keeping these riches for those who come from afar.” The Incas fled, terrified, but not before dubbing the mountain Potojsi, Quechua for “to thunder, burst, explode.”

In 1545, during the early days of the conquest, the prophecy of the mountain came true. An unlucky Indian named Huallpa spent a shivering night on the Cerro, after passing the day in pursuit of an escaped llama. By the light of his campfire, he glimpsed a huge vein of pure silver glittering on the mountain’s surface. Word spread quickly, and, as Galeano puts it, “the Spanish avalanche was unleashed.”

The Spaniards opened the mine that same year. Within three decades, Potosí had grown more affluent than Paris or London, making it the New World’s first genuine boom town. The Holy Roman Emperor, Charles V, named Potosí an Imperial City, and upon its shield were inscribed the lines “I am rich Potosí, treasure of the world, king of the mountains, envy of kings.” Popular theory holds that the old mark of the Potosí mint (the letters ptsi superimposed on one another) was the precursor of the modern dollar sign.

The true amount of silver extracted from the Cerro is impossible to measure, but Bolivians often claim that enough was chiselled from the mountain to build a shimmering bridge from the summit all the way to Madrid. In Spain, even today, if something is “worth a Potosí,” it is worth a fortune. But this astonishing wealth came at an awful cost: untold numbers of indigenous workers perished inside the mines, after living lives of incomparable torment.

Now pay attention,” says Julio. “We are late, so I explain just once.” We crouch, wheezing and coughing and spitting up phlegm, on the lip of a vertical shaft. An antique ladder of rotting wood drops down into the metre-wide hole, as does a manual winch cable. Above, at what would normally be shoulder level, a vein of zinc runs along the ceiling, a glimmering trail criss-crossed by supporting timbers and studded with luminous beauty marks. “The mountain is like my hand,” says our guide. “Its veins are my veins.”

Julio spent two and a half years labouring in the Cerro Rico before quitting to start his guiding company, Green-Go Tours. Now in his early forties, he is a respected mestizo tour guide and professional historian fluent in Quechua, Spanish, and English. “In colonial times, the silver veins were called ‘mother veins,’ thick like the trunks of trees,” he says. “But no one mines silver anymore. Now they mine the branches.”

These days, Potosí is still the highest city in the world, and the Cerro still lords over it like a senile king. But the silver inside the Rich Hill is long gone. By the mid-1800s, miners were sweeping the last breath of silver from these tunnels with brooms, turning their attention to secondary minerals such as zinc and tin. After the Bolivian Revolution in 1952, the government nationalized the tin mines. Then, in October 1985, global prices collapsed and the mine closed, leaving 23,000 unemployed. The face of Potosí became even more worn, as the young fled and older miners, many of whom had spent their entire lives working the Cerro, remained in its shadow.

As necessity — or, more accurately, poverty — is the mother of invention, the veterans quickly banded together to form mining co-operatives. The state, still the legal owner of the Cerro, agreed to lease concessions, and the miners returned to the mountain as their own bosses. Today more than 10,000 destitute mestizo, Quechua, and Aymara Indians scrape a living from the sparse deposits of lead, zinc, and tin still embedded in the Cerro’s warren of exhausted halls. Most are members of one of several dozen co-ops; collectively, they operate more than 300 active mines, many of which date back to the conquest.

“But remember,” says Julio, pointing to the zinc in the ceiling, “we don’t take everything. If we take everything, the mountain will collapse.”We begin our descent. Visceral images of disaster flood my mind as I pick my way down the rickety ladder. Every year, dozens of miners are crushed, suffocated, or blown to pieces inside the Cerro. Cave-ins occur almost weekly, and lethal pockets of carbon monoxide and sulphurous gases lurk behind every wall. Winches fail, cables snap, trolleys run out of control, blasting caps are fumbled to the ground — and yes, old ladders routinely snap. Safety is more than a passing concern down here, but few can afford its wages. Julio installed these ladders himself, to make La Negra more accessible for visitors. Until a few years ago, miners scrambled up and down the shafts using nothing but measures of knotted rope.

On the next level down, we turn acrobatics through the gloom, across the shaky, mud-slick timbers that lie between us and a ten-metre plummet. As we go deeper, the walls begin to play tricks, supporting me until I lose my footing, then backing off and leaving me dangling, scrambling for purchase. At level three, crawling on hands and knees toward the next ladder, I become lodged in a particularly narrow section. For a short, terrifying moment, I am trapped. I can’t move my arms or draw a proper breath. I curse the backpack that, ludicrously, I hadn’t thought to remove. The more I struggle, the more wedged I become.