France, West Germany, Italy, Belgium, the Netherlands, and Luxembourg eliminated all remaining tariffs on trade among themselves and adopted a common external tariff, a milestone that transformed the 1957 Treaty of Rome's aspirations into concrete economic reality. The achievement, completed early, gave momentum to deeper European integration that would eventually produce the single market and the euro.
When the Treaty of Rome established the European Economic Community in 1957, skeptics doubted six nations with wildly different economies and recent histories of war could coordinate trade policy at all, let alone ahead of schedule. Yet by July 1, 1968, internal customs duties had vanished completely, years earlier than the treaty's own twelve-year transition period required.
The customs union created a genuine common market for goods, forcing member states to negotiate trade policy collectively with the rest of the world rather than individually. It proved that pooled sovereignty could work in practice, not just theory, emboldening European leaders to pursue further integration: the 1970s monetary snake, the 1986 Single European Act, and eventually the Maastricht Treaty's common currency. The achievement is often overshadowed by later, flashier EU milestones, but without this quiet customs breakthrough the rest may never have followed.