The Spanish dollar, originally known as the piece of eight (Spanish: real de a ocho, peso duro, peso fuerte or peso), and much later also dólar is a silver coin of approximately 38 mm (1.5 in) diameter worth eight Spanish reales. It was minted in the Spanish Empire following a monetary reform in 1497 with content 25.563 g (0.8219 ozt) fine silver. It was widely used as the first international currency because of its uniformity in standard and milling characteristics. Some countries countermarked the Spanish dollar so it could be used as their local currency.
Because the Spanish dollar was widely used in Europe, the Americas, and the Far East, it became the first world currency by the 16th century.