On March 25, 1957, Belgium, West Germany, France, Italy, Luxembourg, and the Netherlands inked the treaty that established the European Economic Community in an ancient building on Capitoline Hill in Rome.

The document was one that cemented European countries, six at first and now 28, into a single market.

With the United Kingdom officially set to leave the group soon, the leaders of the 27 members will gather in Rome on Saturday to mark the 60th anniversary of the signing of the treaty.