Originally a Roman, and later, a Moorish mining settlement when taken from the Visigoths, the town was captured by the Christians in 1151 under king Alfonso VII and given to the Knights of the Order of Calatrava.

Almadén is home to the world's greatest reserves of cinnabar, a mineral associated with recent volcanic activity, from which mercury is extracted.

[4][5] From antiquity, cinnabar was used to make the pigment vermillion and this is the likely end-use of the mineral extraction of Almadén of the Roman and Visigothic periods, for which times historical records are limited.

With the more advanced expertise available to the alchemists of Al-Andalus, the mines of Almadén exported mercury throughout the entire Mediterranean basin.

[2] The Fuggers of Augsburg, two German bankers, administered the mines during the 16th and 17th centuries in return for loans to the Spanish government.

[6][7] After the Fuggers failed to meet production quotas in 1566, the King of Spain agreed to send 30 prisoners to serve their sentences as laborers at Almadén.

Murderers and capital criminals were rarely selected, as the galleys were considered a far harsher punishment than the mines of Almadén.

[7] A steady run of complaints to the king in the 1580s led to an investigation of convict living conditions at Almadén in 1593.

The investigation was conducted by royal commissioner and famous author Mateo Alemán and was based largely on convict interviews.

Common symptoms included severe pains in any part of the body, trembling limbs, and loss of sanity.

[7] People abducted for slavery, mainly from North Africa, were purchased directly from slaveholders to work alongside the convicts.

The enslaved people purchased to work in the mines at Almadén were those considered less desirable, unwanted by their slaveholders for various reasons ("rebelliousness", for example), so were much cheaper than others on the market at the time.

Such were the dangers of the work and the likelihood of early death, that purchasing enslaved people at the usual market price would have been uneconomic.

In 1981, the Spanish government created the company Minas de Almadén y Arrayanes to operate the mine.

[2] The International Union of Geological Sciences (IUGS) acknowledged Almadén as "the largest known mercury deposit in the Earth and with a longest productive history dating back to the 3rd century BCS".

Due to this, IUGS included "the giant mercury deposit of the Almadén syncline" in its assemblage of 100 world "geological heritage sites" published in October 2022.