Potosí Silver Mines (1545): Cerro Rico and Spain's Treasure

The Potosí silver mines at Cerro Rico, the “Rich Mountain” in present-day Bolivia, were the greatest source of silver in the early modern world. Mining claims were registered in April 1545, and within a few decades Potosí was one of the largest cities in the Americas. Its silver financed the Spanish monarchy and flowed through Europe to China, but it was produced largely by Indigenous forced labour.

Discovery in 1545

The Cerro Rico is a cone-shaped mountain rising to about 4,800 metres, in the high Andes of what the Spanish called Upper Peru. The region had been part of the Inca Empire before the Spanish conquest of the Inca Empire in the 1530s.

According to tradition, an Indigenous herder or miner named Diego Huallpa found a rich vein of silver ore early in 1545. Spaniards from the nearby mining centre of Porco quickly staked claims, which were registered in April 1545. A rush followed, and a settlement grew rapidly at the foot of the mountain, at an altitude of about 4,000 metres.

Early mining and decline

In the first two decades the richest ores lay near the surface. Indigenous workers, many of them skilled miners, smelted the ore in small clay wind furnaces called huayras, which used the strong mountain winds to reach high temperatures. Much of the early production was in Indigenous hands, with Spanish owners taking a share.

By the 1560s the high-grade surface ore was running out and production fell sharply. Smelting poorer ore was not profitable, and the colony’s rulers looked for new methods.

Toledo’s reforms: mercury and the mita

The turning point came under Francisco de Toledo, viceroy of Peru from 1569 to 1581. In the early 1570s he introduced the mercury amalgamation process at Potosí, which allowed lower-grade ore to be refined profitably. The mercury came mainly from Huancavelica in Peru, where a large deposit had been found in the 1560s.

Toledo also built a network of reservoirs and channels to power water-driven ore crushers, and he organised the mita. This adapted an Inca labour obligation into a forced draft for the mines. From 1573, Indigenous communities across a wide area of the southern Andes had to send about one-seventh of their adult men to Potosí each year, a total of roughly 13,000 to 14,000 workers.

Mitayos received low wages that rarely covered their costs, and many travelled hundreds of kilometres with their families. Work underground was dangerous, with falls, cave-ins, cold and exhaustion, while refining exposed workers to mercury poisoning. Many communities paid money to escape the draft, and others saw men flee rather than serve. Wage labourers, called mingas, also worked alongside the mitayos in large numbers.

The refining works, or ingenios, lined a stream known as the Ribera that ran through the town, fed by artificial lakes built in the hills above. Ore was crushed by water-powered stamps, mixed with mercury, salt and other ingredients in large patios or tanks, and then heated to drive off the mercury and leave silver. The system tied Potosí to Huancavelica, more than 1,000 kilometres away, where mercury miners faced deadly poisoning of their own.

Toledo’s reforms were part of a broader reorganisation of Andean society. He forced many Indigenous people into new planned towns, called reducciones, which made it easier to collect tribute, recruit mita labour and convert people to Christianity.

The silver city

With Toledo’s reforms, output soared and peaked in the 1590s. Potosí grew into a wealthy, crowded city, with dozens of churches, a royal mint established in the 1570s, gambling houses and imported luxuries carried up from the coast by llama and mule. Contemporary counts put the population at up to 160,000 in the early 17th century, though historians often suggest somewhat lower figures.

The city lay in the Audiencia of Charcas, part of the Viceroyalty of Peru. Silver travelled overland to the Pacific port of Arica, by sea to Lima and Panama, and across the Atlantic to Seville. Spanish silver coins, especially the real de a ocho or “piece of eight”, became a currency accepted around the world.

Silver and the world economy

Potosí silver paid for much of Spain’s military effort in Europe under Philip II and his successors, although much of it quickly left Spain to pay debts and buy goods. Historians have linked the influx of American silver to rising prices in 16th-century Europe, though population growth and other factors also mattered.

A large share of American silver ended up in China, where demand for silver was high. Some crossed the Pacific on the Manila galleons, and some travelled via Europe and the Indian Ocean. This trade is a key part of the Columbian Exchange and of the first truly global economy.

Decline, revival and independence

From the early 17th century output fell gradually as ores became poorer and deeper, flooding increased and the mita supplied fewer workers. Many Indigenous men avoided the draft by moving away from their home communities, and some communities paid cash instead of sending workers, which mine owners sometimes accepted in place of labour. In the late 1640s a major scandal over underweight, debased coins from the Potosí mint damaged trust in Spanish silver money and led to a royal investigation and severe punishments.

In the 18th century production recovered, helped by royal measures such as cutting the Crown’s tax on silver and supplying mercury more cheaply. In 1776 Potosí and the rest of Upper Peru were transferred to the new Viceroyalty of the Río de la Plata, with its capital at Buenos Aires, and much of the silver now left through the Atlantic port there.

The wars of independence brought armies from Buenos Aires and Peru through Potosí several times after 1810. In 1825 Upper Peru became the independent Republic of Bolivia, named after Simón Bolívar, who visited Potosí that year. The Spanish Cortes of Cádiz had already voted to abolish the mita in 1812.

Myths and facts

Myth: Eight million people died in the mines of Potosí. This often-repeated figure has no basis in colonial records and is far higher than the total population of the region. Historians agree that mortality, illness and disruption caused by the mines and the mita were very severe, but they do not support a precise death toll of this kind.

Fact: Potosí remained productive for centuries. Output declined after about 1650 but revived in the 18th century, and mining for silver, tin and other metals continues today.

By the numbers

Timeline

• 1545, April: Spanish mining claims at the Cerro Rico are registered.
• 1560s: Rich surface ores are exhausted and output falls.
• 1569: Francisco de Toledo becomes viceroy of Peru.
• 1572-1573: Mercury amalgamation is introduced and the mita is organised.
• 1590s: Potosí silver output reaches its peak.
• 1825: Potosí becomes part of independent Bolivia.
• 1987: The City of Potosí is listed as a UNESCO World Heritage Site.

Why it matters

Potosí turned a single mountain into an engine of global trade, linking the Andes to Seville, Antwerp and Beijing. It also stands as one of the clearest examples of how colonial wealth was built on the forced labour of Indigenous peoples.