Forgotten lessons for the Eurozone

A Monetary Union is one where there is a single fiat currency with a single monetary authority (a central bank). It also has a single interest and exchange rate, and a single legal entity responsible for issuing that currency across a geographic area. This combination of features required for a true monetary union suggests that many previous monetary unions, including the Latin Monetary Union (LMU) and the Scandinavian Monetary Union (SMU) were not proper monetary unions as such, while the Austro-Hungarian Monetary Union (AHMU) was and the Eurozone is.