At that time, the European Commuinty for Carbon and Steel was still in controle of the mutual emission.
Altought there's a common design in the 1957 stamps, not all countries followed that design.
The theme of 'peace and welfare through agriculture and industry' is respected by all participating countries.
Belgium, Luxemburg, France, West Germany and (at that time, the independent) Saarland, chose agriculture as topic.
Again here, Luxemburg (mint) is the most expensive set. The cancelled stamps I have, contains 2 CTO cancels (3 and 4 francs).