The national side of the German 1, 2 and 5-cent coins is decorated with an oak twig. Oak leaves, used as a symbol for many centuries, have featured on coins in Germany since the Munich Coin Treaty of 1837. This was an agreement between states in southern and central Germany establishing a common currency area.
Euro coins and banknotes were introduced on 1 January 2002 in twelve countries. Today, the euro area has grown to include 18 countries. Euro coins feature a common design on one side. Also, the national side (reverse) of every coin includes a ring of 12 stars from the European Union flag. Each country has its own design for the national side of its coins.