Page "Gold standard" Paragraph 7

Silver pennies, based on the Roman Denarius, became the staple coin of Britain around the time of King Offa, circa AD 796, and similar coins, including Italian denari, French deniers, and Spanish dineros circulated throughout Europe.

Following the Spanish discovery of great silver deposits at Potosí in Bolivia and in Mexico during the 16th century, international trade came to depend on coins such as the Spanish dollar, Maria Theresa thaler, and, in the 1870s, the United States Trade dollar.