The summits were only formalised in the period between 1974 and 1988. At the December summit in Paris in 1974, following a proposal from then-French president Valéry Giscard d'Estaing, it was agreed that more high level, political input was needed following the "empty chair crisis" and economic problems. The inaugural "European Council", as it became known, was held in Dublin on 10 and 11 March 1975 during Ireland's first Presidency of the Council of Ministers. In 1987, it was included in the treaties for the first time (the Single European Act) and had a defined role for the first time in the Maastricht Treaty. At first only a minimum of two meetings per year were required, which resulted in an average of three meetings per year being held for the 1975–1995 period. Since 1996, the number of meetings were required to be minimum four per year. For the latest 2008–2014 period, this minimum was well exceeded, by an average of seven meetings being held per year. The seat of the Council was formalised in 2002, basing it in Brussels. Three types of European Councils exist: Informal, Scheduled and Extraordinary. While the informal meetings are also scheduled 1½ years in advance, they differ from the scheduled ordinary meetings by not ending with official "Council conclusions", as they instead end by more broad political "Statements" on some cherry picked policy matters. The extraordinary meetings always end with official "Council conclusions" - but differs from the scheduled meetings by not being scheduled more than a year in advance, as for example in 2001 when the European Council gathered to lead the European Union's response to the 11 September attacks.