Brussels and the European Union a provisional seat, though with the Common Assembly in Strasbourg as that was the only city with a large enough hemicycle (the one used by the Council of Europe). This agreement was temporary, and plans were set to relocate the institutions to Saarbrücken which would serve as a "European District", but this did not occur. The 1957 Treaties of Rome established two new communities, the European Economic Community (EEC) and the European Atomic Energy Community (Euratom). These shared the Assembly and Court of the ECSC but created two new sets of Councils and Commissions (equivalent to the ECSC's High Authority).
European Economic Community compromise was reached with the Luxembourg compromise on 29 January 1966 whereby a gentlemen's agreement permitted members to use a veto on areas of national interest. On 1 July 1967 when the Merger Treaty came into operation, combining the institutions of the ECSC and Euratom into that of the EEC, they already shared a Parliamentary Assembly and Courts. Collectively they were known as the "European Communities". The Communities still had independent personalities although were increasingly integrated. Future treaties granted the community new powers beyond simple economic matters which had achieved a high level of integration. As it got closer to