a system where gold coins do not circulate, but authorities like central banks agree to exchange circulating currency for gold bullion at a fixed price. First emerging in the late 18th century to regulate exchange between London and Edinburgh, Keynes (1913) noted how such a standard became the predominant means of implementing the gold standard internationally in the 1870s. Restricting the free circulation of gold under the Classical Gold Standard period from the 1870s to 1914 was also needed in countries which decided to implement the gold standard while guaranteeing the exchangeability of huge amounts of legacy silver coins into gold at the fixed rate (rather than valuing publicly-held silver at its depreciated value). The term limping standard is often used in countries maintaining significant amounts of silver coin at par with gold, thus an additional element of uncertainty with the currency's value versus gold. The most common silver coins kept at limping standard parity included French 5-franc coins, German 3-mark thalers, Dutch guilders, Indian rupees, and U.S. Morgan dollars. Lastly, countries may implement a gold exchange standard, where the government guarantees a fixed exchange rate, not to a specified amount of gold, but rather to the currency of another country that is under a gold standard. This became the predominant international standard under the Bretton Woods Agreement from 1945 to 1971 by the fixing of world currencies to the U.S. dollar, the only currency after World War II to be on the gold bullion standard. History before 1873 Silver and bimetallic standards until the 19th century The use of gold as money began around 600 BCE in Asia Minor and has been widely accepted ever since, together with various other commodities used as money, with those that lose the least value over time becoming the accepted form. In the early and high Middle Ages, the Byzantine gold solidus or bezant was used widely throughout Europe and the Mediterranean, but its use waned with the decline of the Byzantine Empire's economic influence. However, economic systems using gold as the sole currency and unit of account never emerged before the 18th century. For millennia it was silver, not gold, which was the real basis of the domestic economies: the foundation for most money-of-account systems, for payment of wages and salaries, and for most local retail trade. Gold functioning as currency and unit of account for daily transactions was not possible due