The Royal Mint in London has recently initiated the replacement of the traditional round one pound coin with a twelve sided bimetallic coin. It is a limited departure from the usual round coins, which follows the model of the 20 pence and 50 pence coins which are also polygonal. It also points to the fact that conventions are there to be challenged and that they have a limited historical reality and are not an eternal truth.
While early coins in the seventh century BCE were very small ingots of a mixture of silver and gold, with the shape of a drop of metal, roughly countermarked with images of bull and lion on one side and an archer on the other, they rapidly stabilized in the Mediterranean economy in the shape of a relatively regular round metallic disk. The early Roman Republic kept using rough bronze ingots and their crude subdivisions, often in nuggets (aes rude), and only in the third century BCE did the Roman coinage become round, contributing to a pluri-millenial domination of round coins.
There have been several instances in which coinage has returned to its original form as an ingot of precious metal. In Sweden in the seventeenth and eighteenth century large bronze plates were minted, taking advantage of rich copper supplies in the country and making the coinage too heavy to transport (some pieces reached a weight of 14 kgs). A side effect of the inconvenience of such large and heavy pieces for ordinary circulation was that Sweden developed paper money before other European countries and founded a government controlled banknote issuing bank, the Sveriges Riksbank,as early as 1668, before the creation of the Bank of England. The Russian Empire imitated the large copper plates in the eighteenth century, as in this Grivna of Tzarina Catherine I (the widow of Peter the Great), dated 1726, illustrated here through a twentieth century copy.
In the sixteenth and seventeenth century cities under siege in northern Europe reverted to the emergency practice of cutting squares of metal from silverware or other materials and minted square coins, also known as klippe, as in this 1/6 Thaler from the Archbishop of Salzburg in 1677.
Early forms of coinage in India were punch-marked on irregular pieces of metal, often square in the case of copper coins. In Japan, the copper currency was composed of round copper coins with a square hole in the middle, used to bundle coins together in the required numbers. As late as 1859-68, coinage included rectangular silver pieces and oval gold pieces. This was just before the beginning of the Meiji Revolution which modernized Japanese society, moving from the feudal samurai culture to the adoption after 1867 of a model of European industrial revolution. We have here illustrated a Bu or silver Ichibu piece, which disappeared as a consequence of modernization along European lines, including the adoption of the gold standard in 1871, with a decimalized monetary system and exclusively full round coins.
In China the old monetary system included privately melted silver ingots, taking the shape of the container in which private silversmiths poured the hot liquid metal before it solidified and could be used as a currency which was valued simply according to its weight and purity. We have here illustrated one of those pieces, which were produced and used in China until World War II.
Finally during the twentieth century experiments with coinage with in shapes were conducted in European states, in some of their colonies, and in India. In the end, round coins or polygonal coins, almost round, remained popular with the public. As an example the last illustration presents two quadrangular coins with rounded corners, issued in the Netherlands (5 cents of Gulden, 1923) and in India (5 paise, 1975), as well as a hexagonal wartime piece from the Belgian Congo (2 francs, 1943) and a flowered colonial piece from Hong Kong (2 dollars, 1995).