No one is certain how much silver has been extracted from Cerro Rico over its four centuries of productivity, but a popular boast was that the Spanish could have constructed a silver bridge to Spain and still had silver left to carry across it. The Spanish monarchy, mortgaged to the hilt by foreign bankers, came to rely completely on the yearly treasure fleets that brought the Potosí silver. On the rare occasions when they were intercepted by storms or pirates, it was a national disaster.

Although the tale of Potosí’s origins probably takes a few liberties with the facts, it’s a good story. It begins in 1544 when a local Inca, Diego Huallpa, searching for an escaped llama, stopped to build a fire at the foot of the mountain known in Quechua as ‘Potojsi’ (meaning ‘thunder’ or ‘explosion,' although it might also have stemmed from potoj, ‘the springs’). The fire grew so hot that the very earth beneath it started to melt and shiny liquid oozed from the ground.

Diego immediately realized he had run across a commodity for which the Spanish conquerors had an insatiable appetite. Perhaps he also remembered the Inca legend associated with the mountain, in which Inca Huayna Capac had been instructed by a booming voice not to dig in the hill of Potojsi, but to leave the metal alone, because it was intended for others.

Whatever the truth of this, the Spanish eventually learned of the enormous wealth buried in the mountain of Potojsi and determined that it warranted immediate attention. On April 1, 1545, the Villa Imperial de Carlos V was founded at the foot of Cerro Rico, thousands of indigenous slaves were forced into service, and large-scale excavation began.

The work was dangerous, however, and so many workers died of accidents and silicosis pneumonia that the Spanish imported millions of African slaves to augment the labor force. The descendants of the very few to survive mainly live in the Yungas.

In order to increase productivity, in 1572 the Viceroy of Toledo instituted the Ley de la Mita, which required all indigenous and African slaves over the age of 18 to work shifts of 12 hours. They would remain underground without seeing daylight for four months at a time, eating, sleeping and working in the mines. When they emerged from a ‘shift,' their eyes were covered to prevent damage from the bright sunlight.

Naturally these miners, who came to be known as mitayos, didn’t last long. Heavy losses were also incurred among those who worked in the ingenios (smelting mills), as the silver-smelting process involved contact with deadly mercury. In all, it’s estimated that over the three centuries of colonial rule (1545–1825) as many as eight million Africans and indigenous Bolivians died in these appalling conditions.

In 1572 a mint was established to coin the silver, reservoirs were constructed to provide water for the growing population and European consumer goods found their way up the llama trails from Arica and Callao. Amid the mania, more than 80 churches were constructed and Potosí’s population grew to nearly 200,000, making it one of the largest cities in the world.

As with most boom towns, Potosí’s glory was not to last. The mines’ output began to decline in the early 19th century and the city was looted during the independence struggles in Alto Perú. The population dropped to less than 10,000 and the mid-19th-century drop in silver prices dealt a blow from which Potosí has never completely recovered.

In the present century only the demand for tin has rescued Potosí from obscurity and brought a slow but steady recovery. Zinc and lead have now taken over from tin as Bolivia’s major metallic exports, but silver extraction continues on a small scale.

Most of the operations in Cerro Rico today are in the control of miner-owned cooperatives, which operate under conditions that have changed little from the colonial period. The dream of the lucky strike (there are still a few) keeps them going, although the number of miners is steadily dwindling.