Latin Monetary Union

The Latin Monetary Union (LMU) was a 19th-century attempt to unify several European currencies into a single currency that could be used in all the member states, at a time when most national currencies were still made out of gold and silver. It was established in 1865 and disbanded in 1927. Many countries minted coins according to the LMU standard even though they did not formally accede to the LMU treaty.

The LMU adopted the specifications of the French gold franc, which had been introduced by Napoleon I in 1803 and was struck in denominations of 5, 10, 20, 40, 50 and 100 francs, with the 20 franc coin (6.45161g of .900 fine gold struck on a 21mm flan) being the most common. In the French system the gold franc was interchangeable with the silver franc based on an exchange ratio of 1:15.5, which was the approximate relative value of the two metals at the time of the law of 1803.

By treaty dated 23 December 1865,France, Belgium, Italy, and Switzerland formed the Latin Monetary Union. They agreed to a combined gold and silver standard (Bimetalism) with a gold-to-silver ratio of 15.5 to 1 as established in the French Franc. One LMU Franc represented 4.5 grams of fine silver or 0.290322 gram of fine gold.

The treaty required that all four contracting states strike freely exchangeable gold coins and silver coins according to common specifications. Before the treaty, for example, the fineness of the silver coins in the four states varied from 0.800 to 0.900. The treaty required that the largest silver coin of 5 francs be struck 0.900 fine and the fractional silver of 2 francs, 1 franc, 50 centimes and 20 centimes all be struck at 0.835 fine. The agreement came into force on 1 August 1866.

The LMU served the function of facilitating trade between different countries by setting the standards by which gold and silver currency could be minted and exchanged. In this manner a French trader could accept Italian lire for his goods with confidence that it could be converted back to a comparable amount of francs.

...
Wikipedia