The first recorded attempt at forging a common currency was made by the Athenians 2,500 years ago. They introduced nifty little coins with an owl on them to be used in markets across their domains. The scheme never really took off until after the collapse of Athens when the coins came to dominate international trade.
27BC to AD476
The Roman empire oversaw the most successful monetary union to date. The silver denarius and gold aureus became the principal coins used all over Europe. The system collapsed with the empire.
Emperor Constantine introduced a common coin for the Byzantine empire, the solidus, which proved remarkably popular and was used as far north as Britain.
There were a number of trade coinages used across borders in medieval Europe. These included sterling, used in Britain, the Netherlands, north- west France and Germany; the florin of the city states of Genoa and Florence, which had 130 versions used all over Europe; and the Venetian ducat, used in most eastern Mediterranean trade.
Belgium, France, Italy and Switzerland adopted a single currency known as Latin Monetary Union. They did so to counteract the instability of the French franc, whose coins were made out of both gold and silver and were therefore susceptible to price fluctuations in the markets. Greece joined LMU in 1876 and it quickly became the unofficial tender of several other European countries. The UK even considered joining in 1867.
The Scandinavian countries formed a successful monetary union until the Second World War caused the system to collapse.
Belgium and Luxembourg joined their monetary systems, their coins and notes becoming interchangeable.
An exhibition about the history of European monetary unions is at the British Museum until 10 January.