The most difficult EU riddles

The bank is based in Frankfurt, the largest financial center in the Eurozone (although not the largest in the European Union). Its location in the city is fixed by the Amsterdam Treaty along with other major institutions.

50% of the natural gas production in the Netherlands comes from the Groningen Gas Field, being the largest natural gas field in Europe and the tenth largest in the world. The other 50% being supplied by around 300 smaller fields, mostly in the North Sea.

Europe Day held on 9 May every year celebrates peace and unity in Europe. The date marks the anniversary of the historical 'Schuman declaration'. At a speech in Paris in 1950, Robert Schuman, the then French foreign minister, set out his idea for a new form of political cooperation in Europe, which would make war between Europe's nations unthinkable.

The number of stars on the flag (designed in 1955) does not vary according to the members of the organization. They are intended to represent all the peoples of Europe, even those outside European integration.

According to the 2016 estimate, the EU population is 510,056,011