No one is exactly sure how such a process would unfold. There are no written rules to address how a country would exit the eurozone.

It’s often said the EU is like a bicycle: it must move forward or else it will topple over. As the crisis over the euro spreads, the bicycle has all but come to a crashing halt and is tilting dangerously to the side.

As bad as the continent’s debt woes are, Europhiles are even more concerned about the cracks appearing in the most fundamental element of modern Europe: unrestricted movement.

While the call by Guben’s mayor for border controls has fallen on deaf ears in Berlin, in other parts of Europe barriers are already going up. Denmark re-established checks at its land border with Germany and at its bridges and seaports in July with the stated goal of stopping illegal immigrants and criminals who have breached the outer edges of Europe’s border-free zone. Under the Schengen agreement, signed in 1985 and of which Denmark is a signatory, members can only impose controls at inner borders on a temporary basis “in the event of a serious threat to public order or national security.” No such threat exists, yet customs officials have been pulling over random cars. Justifying the new restrictions, Danish Finance Minister Claus Hjort Frederiksen alleged: “We have seen too many examples of violence, break-ins and brutal criminality committed by perpetrators who have crossed the borders.”

The reaction from the rest of Europe has been quick and hostile. Germany’s minister for justice and the EU, Jörg-Uwe Hahn, urged Germans to vacation in Poland or Austria rather than Denmark. Danish tourism agencies, which usually profit from renting summer cottages to Germans, have reported cancellations and complaints.