Tuesday, in an effort to protect that ease of movement across internal borders, the EU proposed to strengthen the patrols of its external borders significantly.
The European Commission, the EU's executive arm, is proposing the creation of a new agency with stronger powers to keep people who are not legally entitled to enter the EU on the outside of its external borders.
In EU-speak, internal borders are those where a person is inside the EU no matter which side of the border he or she is on -- such as, for one example, that between Germany and France.
The external borders are those that, when traversed, take a person from outside the EU to inside it.
"In an area of free movement without internal borders, managing Europe's external borders must be a shared responsibility," said Frans Timmermans, the commission's first vice president.
"The crisis has exposed clear weaknesses and gaps in existing mechanisms aimed at making sure that EU standards are upheld."
Agency would include a risk analysis center
The commission is proposing a European Border and Coast Guard -- a new agency with greater powers than Frontex, the current EU agency that assists national governments with control of external borders.
But it is often the case with the EU that proposals for greater EU powers trigger howls of protest that national sovereignty is being ceded to Brussels. That is likely to be the case with the proposed new agency.
In contrast to Frontex, the new agency would be empowered to respond a crisis without first getting the permission of the country involved.
Still, many Europeans perceive a need for stepped up control of the external borders.
The EU said that between January and November, an estimated 1.5 million people crossed the external borders illegally -- an all-time high. And that figure does not count the 1 million who applied for international protection as refugees.
Beyond that, the new agency, if the European Parliament and the European Council ultimately approve it, would have greater resources, ready access to more equipment and would include a monitoring and risk analysis center to identify possible coming flows of migration.