Europe Day

On the 9th of May 1950, Robert Schuman presented his proposal on the creation of an organised Europe, indispensable to the maintenance of peaceful relations.

This proposal, known as the "Schuman declaration", is considered to be the beginning of the creation of what is now the European Union.
Today, the 9th of May has become a European symbol (Europe Day) which, along with the flag, the anthem, the motto and the single currency (the euro), identifies the political entity of the European Union. Europe Day is the occasion for activities and festivities that bring Europe closer to its citizens and peoples of the Union closer to one another.

http://europa.eu/abc/symbols/9-may/index_en.htm