In 2002, the European Council, the organisation gathering the EU's Heads of State/Government together, also began using the Justus Lipsius building as their Brussels venue. This followed an advanced implementation of a decision by European leaders during ratification of the Nice Treaty to do so at such a time as the total membership of the EU surpassed 18 member states. Prior to this, the venue for European Council summits was in the member state that held the rotating Presidency of the Council of the European Union.