1. Treaty establishing the European Coal and Steel Community (1952)
Purpose: to create interdependence in coal and steel so that one country could no longer mobilise its armed forces without others knowing. This eased distrust and tensions after WWII. The ECSC treaty expired in 2002.
Full text of the Treaty establishing the European Coal and Steel Community
When new countries joined the EU, the founding treaties were amended:
1973 (Denmark, Ireland, United Kingdom)
1981 (Greece)
1986 (Spain, Portugal)
1995 (Austria, Finland, Sweden)
2004 (Czech Republic, Cyprus, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia, Slovenia).
2007 (Bulgaria, Romania)

2. Treaties of Rome - EEC and EURATOM treaties (1958)
Purpose: to set up the European Economic Community (EEC) and the European Atomic Energy Community (Euratom).
Main changes: extension of European integration to include general economic cooperation.