France is reeling from a series of deadly attacks in Paris that left at least 127 people dead and scores more injured. Parisians are recovering today from the carnage visited upon multiple sites across the city Friday night.

In the wake of the attacks, French President François Hollande reimposed border controls. This is both a normal security protocol and a worrying sign for the future of a free Europe.

France is part of the Schengen Area, a collective of 26 countries that enjoy free travel at joint borders. It’s a somewhat confusing pan-European grouping that predates the European Union. It includes 22 of the 28 EU states plus some non-members. The four nations of the European Free Trade Association are part of the Shengen Area, but Ireland and the United Kingdom opted out.

European Commission

Part of the Schengen Agreement allows member nations to routinely reinstall passport and immigration border controls at times of heightened national security. In fact, France was already planning to reinstate border controls later in the month, in advance of the UN climate conference being held in Paris from November 30 to December 11. So the Schengen Area is working the way it’s supposed to: During emergencies, the framework allows nations to retreat to stricter border controls without abandoning the dream of free movement.