The Founding Treaties of the European Union: From Rome to Lisbon

The constitutional architecture of the European Union rests upon a succession of treaties that have transformed a sectoral economic community into a supranational polity. From the Treaty of Rome in 1957 to the Treaty of Lisbon in 2007, each foundational instrument has expanded the scope of integration and deepened the legal principles governing the relationship between the Union and its Member States. The Court of Justice has played a decisive role in this constitutionalisation process, interpreting the treaties as a constitutional charter and establishing doctrines that ensure the effectiveness and uniformity of EU law.

The Treaty of Rome and the European Economic Community

The Treaty establishing the European Economic Community (EEC), signed in Rome on 25 March 1957 by Belgium, France, Italy, Luxembourg, the Netherlands, and West Germany, created a common market based on the free movement of goods, persons, services, and capital. It established institutional structures — a Commission, a Council, a Parliamentary Assembly, and a Court of Justice — endowed with law-making and adjudicative powers transcending traditional intergovernmental cooperation. The Treaty also introduced a common commercial policy, competition rules, and provisions for economic and social cohesion. Although primarily economic in approach, its institutional architecture and legal mechanisms contained the seeds of political integration.

The Single European Act 1986

The Single European Act (SEA), entering into force on 1 July 1987, constituted the first major revision of the Treaty of Rome. Its central achievement was the establishment of the internal market — “an area without internal frontiers” — with a deadline of 31 December 1992. The SEA introduced qualified majority voting in the Council for internal market measures under what became Article 114 TFEU, replacing unanimity that had often paralysed decision-making. It also established a cooperation procedure granting the European Parliament a greater consultative role and created the Court of First Instance (now the General Court) to alleviate the caseload of the Court of Justice.

The Treaty of Maastricht 1992 and the Creation of the European Union

The Treaty on European Union, signed in Maastricht on 7 February 1992, represented the most far-reaching reform of the European architecture. It created the European Union and established the three-pillar structure: the European Communities as the supranational first pillar; the Common Foreign and Security Policy as the second, intergovernmental pillar; and Police and Judicial Cooperation in Criminal Matters as the third pillar. Maastricht introduced European citizenship, conferring the right to move and reside freely within the Member States, the right to vote and stand in local and European Parliament elections in the Member State of residence, and diplomatic protection by any Member State’s authorities. The Treaty also established the framework for Economic and Monetary Union, including convergence criteria for adoption of the single currency and the institutional architecture of the European Central Bank, introduced the co-decision procedure giving the Parliament a genuine legislative role, and formalised the principle of subsidiarity.

The Treaty of Amsterdam 1997

The Treaty of Amsterdam, signed on 2 October 1997 and entering into force on 1 May 1999, incorporated the Schengen acquis into the EU legal order, with opt-outs for the United Kingdom and Ireland. It strengthened social and employment policies, introducing a new Title on employment requiring coordinated employment policies among Member States. Amsterdam transferred visa, asylum, and immigration policy to the first pillar, expanding supranational institutional involvement in these areas. The Treaty codified liberty, democracy, respect for human rights, and the rule of law as foundational values and established the Article 7 TEU mechanism for suspending the rights of a Member State that persistently breaches these values.

The Treaty of Nice 2001

The Treaty of Nice, signed on 26 February 2001 and entering into force on 1 February 2003, was concerned primarily with institutional reform preparing for enlargement from fifteen to twenty-seven Member States. It reformed the composition of the Commission, reweighted Council votes to reflect relative population sizes, extended qualified majority voting to approximately thirty new legal bases, reformed the Court of Justice and the Court of First Instance enabling specialised judicial panels, and adopted a new procedure for enhanced cooperation. The Charter of Fundamental Rights was proclaimed at Nice but was not given binding legal effect.

The Treaty of Lisbon 2007

The Treaty of Lisbon, signed on 13 December 2007 and entering into force on 1 December 2009, represents the current constitutional foundation of the Union. It abolished the three-pillar structure, established the Union as a single legal personality, and created the two-treaty structure: the Treaty on European Union (TEU) containing foundational provisions and the Treaty on the Functioning of the European Union (TFEU) containing substantive policies. Lisbon gave the Charter of Fundamental Rights binding legal effect equal to the Treaties under Article 6(1) TEU, established the European Council as a formal institution with a permanent President, created the office of the High Representative for Foreign Affairs, extended the ordinary legislative procedure to most policy areas, increased the role of national parliaments in subsidiarity scrutiny, and introduced the European Citizens’ Initiative under Article 11(4) TEU.

Constitutional Principles: Primacy, Direct Effect, and General Principles

The Court of Justice has developed foundational doctrines giving the treaties their constitutional character. The primacy of EU law was established in Costa v ENEL (Case 6/64), in which the Court held that Member States had limited their sovereign rights by creating a legal order binding their nationals and themselves, and that EU law cannot be overridden by domestic provisions. Primacy has been confirmed in Internationale Handelsgesellschaft (Case 11/70) and Simmenthal (Case 106/77). The direct effect doctrine, established in Van Gend en Loos (Case 26/63), enables individuals to invoke EU law provisions before national courts where the provisions are clear, unconditional, and not dependent on further implementing measures. The general principles of EU law include proportionality, subsidiarity under Article 5(3) TEU, conferral under Article 5(2) TEU, and legal certainty. The treaty-making power of the Union is governed by Article 216 TFEU. Accession of new Member States under Article 49 TEU requires unanimous Council agreement, European Parliament consent, and ratification by all Member States. Withdrawal under Article 50 TEU was introduced by Lisbon and exercised by the United Kingdom in 2020.