The seven institutions of the European Union (EU) are seated in four different cities, i.e. Brussels, Frankfurt, Luxembourg and Strasbourg, rather than being concentrated in a single capital city. The EU agencies and other bodies are located all across the union, but usually not fixed in the treaties. The Hague is the only exception, as the fixed seat of European Police Office (Europol). Over the years, Brussels has become the principal seat, with each major institution and now the European Council being based wholly or in part there, leading to it being popularly known as 'the capital of the EU'.