Lisbon Subway Map on However, the use of gold as a medium of payment has been in existence for centuries: It was perhaps the only universal form of currency. The introduction of paper money and coinage was made for convenience and safety; carrying gold was not a very safe activity, thus paper currency and coinage became a medium of exchange. In the UNITED STATES, there existed a bimetal standard, using both gold and silver. However, by the middle of the 19th century, the United States converted to a full gold standard and fixed the price of gold in 1834, at $20.67 per ounce. This price did not change until the initial demise of the gold standard during WORLD WAR I. The idea behind the gold standard was for every participating country to fix the price of gold according to their currency, then the exchange rate between currencies could be easily calculated. Lisbon Subway Map 2016.
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