Institutional seats of the European Union are based in Luxembourg City along with the European Investment Bank. The Economic and Social Committee and the Committee of the Regions are entirely based in Brussels while the European Central Bank is based in Frankfurt and Europol is the only agency to have its seat fixed by the treaties, in The Hague. Separately, the Treaty of Nice establishes Brussels as the venue for all formal summits of the European Council after 2004. However some extraordinary sessions are sometimes held outside the city. The European Council's seat is however fixed by a declaration rather than a protocol, meaning it is
Treaties of the European Union – accountable to national parliaments. Article 11 establishes government transparency, declares that broad consultations must be made and introduces provision for a petition where at least 1 million citizens may petition the Commission to legislate on a matter. Article 12 gives national parliaments limited involvement in the legislative process. Article 13 establishes the institutions in the following order and under the following names: the European Parliament, the European Council, the Council, the European Commission, the Court of Justice of the European Union, the European Central Bank and the Court of Auditors. It obliges co-operation between these and limits their competencies