Sainte-Marie-aux-Mines extends in a geological area of numerous faults and fractures. As they infiltrate the ground, surface waters carry the minerals that would form the silver, copper, or lead veins. In medieval France, silver is linked to the minting of coins. The monetary system imitates that of the Romans. The basic unit is the denarius, and the kings created the pound, worth 240 denarii. They also decided to establish the sol, worth 12 denarii, one pound being the equivalent of 20 sols. Silver mines were therefore of paramount importance in the economy of both the region and the country.