Three pillars of the European Union
Between 1993 and 2009, the European Union (EU) legally comprised three pillars. This structure was introduced with the Maastricht Treaty on 1 November 1993, and was eventually abandoned on 1 December 2009 upon the entry into force of the Treaty of Lisbon, when the EU obtained a consolidated legal personality and a structured distribution of competences.
Source: Wikipedia — Three pillars of the European Union (CC BY-SA 4.0)