Almadén Mercury Mine: A Deep Dive into Spain's Most Hazardous Heritage
Almadén in Castilla–La Mancha is the largest mercury reserve in the world. From Roman times to 2003 it produced perhaps a third of all mercury ever mined — most of it shipped to the Americas to refine silver.
Roman beginnings
Pliny the Elder described the cinnabar mines of Sisapo, generally identified with Almadén. Romans extracted vermilion pigment and small amounts of mercury for amalgamation.
The Fugger period
From 1525 to 1645 the Almadén mines were leased to the Augsburg Fugger banking family in payment for loans to the Habsburg emperors. Output rose sharply under their management.
Mercury for Potosí
The discovery of the patio amalgamation process at Pachuca in 1554 transformed Almadén. Mercury was shipped from Seville to Cartagena, then transhipped to Lima and onwards to Potosí — the silver mountain ran on Almadén's output.
Royal monopoly
From the late 17th century the mine was a Spanish royal monopoly. Forced labour of galley slaves and prisoners was used through the 18th century.
The miners' health
Mercury poisoning was endemic. Miners typically lasted five to seven years before disabling tremors and dementia ended their working lives. The hospital of Almadén pioneered the medical study of mercury intoxication.
20th-century operation
Mercury production peaked at over 1500 tonnes a year in the early 1940s. Closure came in 2003 with the Minamata Convention restricting mercury use globally.
UNESCO inscription
Almadén was inscribed jointly with Idrija (Slovenia) in 2012 as 'Heritage of Mercury'.
The visitor experience
Today visitors descend the San Teodoro shaft to 50 m, see the patio amalgamation court and the royal jail, and visit the Fuggers' archive. The Spanish state runs an excellent multimedia museum.
The town
Almadén town itself is built around the mine — including the unique Real Hospital de Mineros (1773), the oldest miners' hospital still standing, and the unusual hexagonal Plaza de Toros.
Explore on the map
Find Almadén Mercury Mine and related mining heritage sites on the interactive map, with opening hours and accessibility notes.