ON MARCH 25th the European Union’s heads of government will gather in the glorious Sala Degli Orazi e Curiazi of Rome’s Palazzo dei Conservatori to issue a solemn declaration of unity. The moment will be freighted with significance: exactly 60 years earlier, as expectant crowds huddled under umbrellas on the Piazza del Campidoglio outside, plenipotentiaries from six Western European countries—France, West Germany, Italy, Belgium, the Netherlands and Luxembourg—assembled in the same room to sign the Treaty of Rome. The 1957 treaty established the institutions that made up the European Economic Community—the European Commission, the Council of Ministers, the European Parliament and the European Court of Justice (ECJ)—which was in time to become the EU. (A second treaty signed that day created the European Atomic Energy Community, later folded into the EU.) What was the significance of the Treaty of Rome?

The treaty emerged from the European Coal and Steel Community (ECSC), signed by the six countries in Paris in 1951, with the ashes from the second world war still smouldering. By uniting industrial production under a centralised authority the ECSC was, in the words of Robert Schuman, France’s foreign minister, designed to make war “not only unthinkable but materially impossible”. It was also intended to pave the way for much deeper forms of integration between the six countries. There were bumps along the way: in 1954 opposition from French MPs killed a proposed European Defence Community, after which the governments focused their efforts on economics and trade. At a conference in Messina, Sicily, in 1955, the six governments agreed to establish a European customs union and common market. A subsequent report by Paul-Henri Spaak, a Belgian politician, provided the roadmap. This created the foundations for the Treaty of Rome.

The treaty established forms of international co-operation that extended far beyond the intergovernmental arrangements familiar to most diplomats. The Council of Ministers and European Parliament (EP) preserved decision-making roles for, respectively, governments and national parliaments (direct elections to the EP began in 1979). But the European Commission was granted independent authority, including the sole power to propose European laws and the duty to oversee its implementation. The ECJ was to turn itself, with the full consent of the member states, into Europe’s supreme judicial authority, and national legal codes were in time to be transformed by the commitments made at Rome. Future treaties extended the powers of each of these institutions, driven always by the pledge made at Rome to work for “ever-closer union among the peoples of Europe.”

For Europhiles the Treaty of Rome marks the moment when Europeans understood that the preservation of peace and prosperity on the continent required a sacrifice of national sovereignty and a commitment to common institutions, and that economic integration would precede the political sort. In time, some hoped, it would be seen as the EU’s Philadelphia moment, although the dreams of true federalists have been repeatedly thwarted. But for Eurosceptics, the treaty was the EU’s moment of original sin. Many such critics were found in Britain, which spent years trying to get into the club and more recently has elected to leave it. (Theresa May, the British prime minister, will not attend this weekend’s festivities.) Writing after the treaty was signed, the Manchester Guardian took a magnanimous view: “If the Common Market, like the Coal and Steel Community, has to start its life by kicking England in the shins, we should be able to disregard the gesture as an old Continental custom.”