At present the most successful common market is of course the European Union. But the EU started out as just a coal and steel community with only six countries. It then turned into the European Economic Community with the signing of the Treaty of Rome in 1957. The EEC was a customs union, with no customs duties between member states, and adoption of a common customs policy towards non-members.
現代最成功的共同市場當然是歐盟，但歐盟剛開始只是 6 個國家的煤鋼聯營，然後 1957 年簽訂羅馬條約時變成歐洲經濟共同體（EEC），EEC 本身是關稅同盟，會員國內部之間沒有關稅，對外則採取共同的關稅政策，也就是不管對內對外，大家都立場一致。