The silver standard is a monetary system in which the standard economic unit of account is a fixed weight of silver. The silver specie standard was widespread from the fall of the Byzantine Empire until the 19th century. Following the discovery in the 16th century of large deposits of silver at the Cerro Rico in Potosí, Bolivia, an international silver standard came into existence in conjunction with the Spanish pieces of eight. These silver dollar coins played the role of an international trading currency for nearly four hundred years.