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 the ECSC and Euratom were merged with that of the EEC, creating a single institutional structure governing the three separate Communities. From here on, the term "European Communities" were used for the institutions (for example, from "Commission of the European Economic Community" to the "Commission of the European Communities"). The Council of the European Communities was a body holding legislative and executive powers and was thus the main decision making body of the Community. Its Presidency rotated between the member states every six months and it is related to the European Council, which was an informal gathering of national leaders