The roots of the Treaty of Rome run back into the still-fresh ruins of the war. On 9 May 1950 French foreign minister Robert Schuman, working from a plan drafted by Jean Monnet, proposed that France and West Germany pool their coal and steel production under a common high authority. The logic was simple and revolutionary: pool the industrial basis necessary for two countries to wage war on each other and war becomes 'not merely unthinkable but materially impossible.' The Treaty of Paris of 18 April 1951 created the European Coal and Steel Community (ECSC) — France, West Germany, Italy, the Netherlands, Belgium, and Luxembourg. This Six would form the core of European integration for the next decade. In 1954 the European Defence Community project was rejected by the French parliament and the dream of a federal Europe was put on hold; but a committee chaired by the Belgian diplomat Paul-Henri Spaak prepared in 1955–1956 the report that would expand the ECSC into a full common market. The Spaak Report became the skeleton of the Treaty of Rome.

On the morning of 25 March 1957 the signing ceremony took place at the Palazzo dei Conservatori on the Capitoline Hill. The signatories were: for France, Christian Pineau and Maurice Faure; for West Germany, Chancellor Konrad Adenauer and Walter Hallstein; for Italy, Prime Minister Antonio Segni and Gaetano Martino; for Belgium, Spaak and Jean Charles Snoy; for the Netherlands, Joseph Luns and J. Linthorst Homan; for Luxembourg, Joseph Bech and Lambert Schaus. There were two distinct treaties. The EEC (European Economic Community) covered the whole economy: a customs union; free movement of goods, services, capital, and labour (the 'four freedoms'); a common competition policy; a common agricultural policy (CAP); a common trade policy. Euratom established a single market and supervisory system for atomic energy — the pooling of peaceful nuclear power in the Cold War context. The EEC came into force on 1 January 1958; by 1968 internal tariffs had been completely eliminated and a common external tariff applied. The CAP was constructed at French insistence as the price for West Germany's industrial export advantages — a mechanism that would consume roughly two-thirds of the Community's budget through the 1960s.

The Community went through seven major enlargements in its first sixty years: in 1973 Britain (after Charles de Gaulle's vetoes of 1963 and 1967), Ireland, and Denmark; in 1981 Greece; in 1986 Spain and Portugal; in 1995 Austria, Finland, and Sweden; in 2004 the post-Cold War great enlargement (Poland, the Czech Republic, Hungary, Slovakia, Slovenia, Estonia, Latvia, Lithuania, Cyprus, Malta — 10 countries); in 2007 Bulgaria and Romania; in 2013 Croatia. The structure also deepened over the same period: direct elections to the European Parliament in 1979, the Single European Act of 1986 (completion of the single market), the Maastricht Treaty of 1992 creating the European Union (three pillars: the EEC, common foreign and security policy, justice and home affairs), the Schengen area of free movement in 1995, the introduction of the euro in 2002, the Lisbon Treaty of 2009. The Brexit referendum of 23 June 2016 produced the United Kingdom's decision to leave; actual withdrawal took place on 31 January 2020 — the first reverse exit in the project's history.

For Turkey, the Treaty of Rome had direct consequences. On 31 July 1959, two weeks after Greece, Turkey applied for association with the EEC; the Ankara Agreement of 12 September 1963 traced a customs union roadmap — the beginning of what would prove to be a half-century wait. In 1995 the customs union came fully into force; in 1999 Turkey gained official candidate status; in 2005 accession negotiations opened; but from 2016 onwards the negotiations were in effect frozen. Historically, the Treaty of Rome became one of the concrete targets of Turkey's Western-oriented modernisation since 1923 — but also the source of much of the chronic tension in EU–Turkey relations. The wider historical importance of the treaty is clear: in the seventy years since 1957, there has not been a single armed conflict among the six founding countries of Europe or with their immediate neighbours — and that is where the cycle that ravaged the continent from the Thirty Years' War to 1945 stopped. That alone is not sufficient evidence that the 'make war impossible' project succeeded — NATO and other factors matter too — but the two treaties signed in Rome remain the boldest experiment in peace engineering the modern world has attempted.