For many, it's hard to image a Europe without the euro, open borders and the blue flag with 12 gold stars. Names like Churchill, Schuman, and Monnet are inseparable with today's unified Europe.
Could the EU's founders have envisioned a bloc of 27?
Europe began as a vision that slowly gained momentum.
After the tragedy of World War I, intellectuals, politicians and economic leaders saw the need for a European solution. Here's a look at some of the visionaries behind Europe's unification:
Richard Coudenhove-Kalergi (1894-1972)
In 1923, four years after the Treaty of Versailles had ended the war, Richard Coudenhove-Kalergi, an Austrian count and diplomat, published a manifesto entitled "Paneuropa" that would lead to a political movement under the same name.
"Pan-Europe is not a tool of current European politics, rather its counterpart," Coudenhove-Kalergi said. "It's a new source of strength, a new flow of ideas that is getting stronger from year to year. If all the leading statesmen clearly saw the necessity of a federation, Pan-Europe would become a reality within six months."
Although the Pan-Europe movement attracted numerous adherents, it didn't reach fruition quite as quickly as Coudenhove-Kalergi had imagined. When World War II began in 1939, a unified Europe seemed more like farfetched optimism.
Sir Winston Churchill (1874-1965)
Nevertheless, Europe's leaders didn't lose site of the vision. The end of World War II coincided with the dawn of the Cold War, and it was in this context in 1946 that Britain's then minority leader Winston Churchill gave new wind to the notion of a unified Europe.
"If Europe were once united in the sharing of its common inheritance there were be no limit to the happiness, to the prosperity and the glory which its three or four hundred million people would enjoy," Churchill said.
"The structure of the United States of Europe, if well and truly built, would be such as to make the material strength of a single state less important," he continued. "Small nations will count as much as large ones and gain their honor by their contribution to the common cause."
Though Churchill wasn't considered to be a convicted European, his reference to the "United States of Europe" in this speech in Zurich hit the international press and immediately sparked discourse across the globe.
Suddenly, the idea seemed more plausible than ever -- not least because it had been put into words by one of the great victors of World War II.
Robert Schuman (1886-1963)
The actual initiative for European unification came from a Frenchman, however. On May 9, 1950, French Foreign Minister Robert Schuman suggested at a press conference in Paris that the entire French-German coal and steel production be placed under one roof.
This revolutionary proposal foresaw the transfusion of national sovereignty -- an essential element of transnational unification. Schuman also spoke of solidarity between the free states of Europe and a common destiny.
"We will strengthen this feeling by combining our energy and our will, and by dealing trustfully and meeting regularly to coordinate trade," he said.
Jean Monnet (1888-1979)
Although Schuman's name is intricately linked with the birth of a unified Europe, the conceptualizer behind the plan was another French politician, Jean Monnet.
Monnet was convinced that Europe's economic development needed to be organized and that France's wellbeing was dependent on Europe's financial progress.
"For the first time in our history, the restraints that the nations of Europe have placed on our people are beginning to fall," he said. "In spite of material progress,...this society is opening itself to unification -- unification that is indispensable to the Renaissance of our European civilization and for the preservation of peace."
Monnet has also been quoted as countering Churchill's phrase with the statement: "We united people, not states."
Paul-Henri Spaak (1899-1972)
Monnet and Schuman are considered to be the founding fathers of unified Europe. Their less-known contemporary, Paul-Henri Spaak from Belgium, also played a significant role in the formation of the union.
Spaak was named "Monsieur Benelux" for advancing the Benelux trade union between Belgium, the Netherlands and Luxemburg -- which forms part of the core of today's European Union. Spaak also chaired the group of experts that laid the groundwork for the Treaties of Rome, the bloc's founding documents signed on March 25, 1957.