The European District follows the recent releases of items that help us save space in our cities by allowing us to group together more buildings of the same type. The amazing news here is that any European District can hold up to 30 buildings and we are allowed to purchase more than one for the low price of 500,000 coins each. Of course, you can only place European buildings inside the European District, and in order to find which apply, head over to the market and type European in the search box.
An even better news is that the first European District that you build (received from the mission) and each has an European Mall, European Neighborhood and an European Civic Center section (basically allowing you to group the buildings based on their type). Each of these sections will change appearance when you upgrade.
In order to upgrade any section of the European District, you will have to click it and request the 5 different parts (5 of each are required) in order to complete the upgrade.
Good luck getting and completing the European District in CityVille!