Money was historically an emergent market phenomenon that possessed intrinsic value as a commodity; nearly all contemporary money systems are based on unbacked fiat money without use value. Its value is consequently derived by social convention, having been declared by a government or regulatory entity to be legal tender; that is, it must be accepted as a form of payment within the boundaries of the country, for "all debts, public and private", in the case of the United States dollar.
Foreign exchange reserves assets can comprise banknotes, bank deposits, and government securities of the reserve currency, such as bonds and treasury bills. Some countries hold a part of their reserves in gold, and special drawing rights are also considered reserve assets. Often, for convenience, the cash or securities are retained by the central bank of the reserve or other currency and the "holdings" of the foreign country are tagged or otherwise identified as belonging to the other country without them actually leaving the vault of that central bank. From time to time they may be physically moved to the home or another country. (Full article...)
Obverse FERDIN[ANDUS] VII DEI GRATIA 1821"Ferdinand VII by the Grace of God, 1821." Right profile of Ferdinand VII with cloak and laurel wreath
The Spanish dollar, also known as the piece of eight (Spanish: real de a ocho, dólar, peso duro, peso fuerte or peso), is a silvercoin 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, America, and the Far East, it became the first world currency by the 16th century. (Full article...)
... that medievalist Edward Rand rang the doorbell of Harvard president Charles William Eliot and asked him: "I would like to go to Harvard; do you have any money?"
... that Colin Stubs spent the prize money from his first international tennis title on an old Volkswagen to travel around Europe?
... that Ken Kortas lost money speculating on hog futures during his NFL career?
The following are images from various currency-related articles on Wikipedia.
Image 1A 640 BC one-third staterelectrum coin from Lydia. According to Herodotus, the Lydians were the first people to introduce the use of gold and silver coins. It is thought by modern scholars that these first stamped coins were minted around 650 to 600 BC. (from Money)
Image 19Athens coin (c. 500/490-485 BC) discovered in Pushkalavati. This coin is the earliest known example of its type to be found so far east. (from Punch-marked coins)
Image 20Tibetan kong par tangka, dated 13-45 (= AD 1791),reverse (from Tibetan tangka)