I don't think they closed their borders. They invoked the Schengen protocol for re-instituting border controls. Under Schengen driving from France to Italy or Germany is like driving from Texas to Louisiana. But there is a clause allowing re-instituting border controls under certain conditions, including a national security emergency.
>>001sky+44
This was corrected by the President's office, clarifying "closing the borders" as "restoring border controls". As a side note, during Shengen, border police still exists but is allowed to place controls wherever they want. It's not clear to my why controls at the borders is more efficient than intense, random in-land controls.