Mercury is a relatively rare metal, with a decisive role in the extraction of silver and gold, so the possesion of the mercury mines had a worldwide strategic importance. Until recent times, it has been produced in substantial quantities and over a long period only by a small number of mines, of which the biggest were at Almadén in Spain and Idrija in Slovenia. These two mining towns was included on the UNESCO World Heritage Sites list in 2012, because this dual testimony is unique, and it illustrates the various industrial, territorial, urban and social elements of a specific sociotechnical system.
