The AETR judgment shows that powers which, at the outset, have not been conferred exclusively upon the European Community may become so progressively through the exercise of those powers by the Community. In this case, the implementation of a common transport policy by the Community, through the laying down of common rules of an internal nature (adoption of a regulation), excludes the possibility of concurrent powers on the part of the Member States throughout the sphere of transport. The Court of Justice, while aware that the system of internal Community measures may not be separated from that of external relations, concludes that Member States may no longer enter into agreements with third countries in this field.