STOCKHOLM: Since it opened in 2000 the Oresund bridge between Sweden and Denmark has been a towering symbol of European integration and hassle-free travel across borders that people didn't even notice were there.

On Monday new travel restrictions imposed by Sweden to stem a record flow of migrants are transforming the bridge into a striking example of how national boundaries are re-emerging. A year of clampdowns on migration and terrorism has all but killed the idea of a borderless Europe where you could drive or train-hop from Spain in the south to Norway in the north without ever having to show your passport.

"We're turning back the clock" said Andreas Onnerfors who lives in Lund on the Swedish side of the bridge. An associate professor in intellectual history he said he's benefited from the free flow of people and ideas across the bridge — he's studied on both sides and taught students from both Sweden and Denmark.

"We're going back to a time when the bridge didn't exist" he said referring to the ID checkpoints being set up Monday on the Danish side for train passengers wishing to cross over to Sweden.

The move is meant to stop undocumented migrants from reaching Sweden which abruptly reversed its open-door policy after receiving more than 160000 asylum-seekers last year mainly from Syria Iraq and Afghanistan.

It follows the reintroduction of border checks in Germany Austria France Belgium and other countries in what's supposed to be a passport-free travel zone spanning 26 nations.

The moves are supposedly temporary but are likely to be extended if Europe's migrant crisis continues in 2016.

"It's basically every country for itself now" said Mark Rhinard an expert on the European Union at the Swedish Institute of International Affairs.

Citing exceptional national circumstances related to security terrorism and public order several European countries have suspended EU rules that required them to keep their borders open to each other.

It's a significant development that strikes at the very heart of the EU project — the free movement of goods and people across borders.

The Bruegel think tank in Brussels says that in 2014 there were almost 1.7 million cross-border commuters in the passport-free zone known as the Schengen Area after the Luxembourg town where it was created in 1985. Abolishing it would affect their daily lives but the consequences for Europe would go deeper given the "visible and powerful symbol of European integration that Schengen represents" Bruegel researchers Nuria Boot and Guntram Wolff wrote in December.

Whether the temporary reintroduction of borders also means rebuilding mental boundaries between EU citizens remains to be seen. But the migrant crisis is becoming an even bigger challenge to European unity than the cracks emerging in recent years over the bloc's common currency the euro.

EU nations demonstrated starkly different views on how to deal with the 1 million migrants that crossed the Mediterranean in 2015. Germany and Sweden until recently said refugees were welcome while Hungary built a fence to keep them out. The Danish government took a series of measures to discourage migrants from going there including a proposal to seize their jewelry to cover their expenses in Denmark.

Common rules requiring refugees to seek shelter in the first EU country they enter collapsed as Greece and Italy were overwhelmed by sea arrivals and countries further north just waved the migrants through to their intended destination often Germany or the Scandinavian countries.

Meanwhile the EU's efforts to spread refugees more evenly across the bloc met stiff resistance from member states. By November only about 150 of 160000 refugees had been relocated from Greece and Italy under an EU plan.

The crisis underlines structural flaws in the EU showing how it has implemented common rules that it just can't enforce once the external pressures become too great said Karl Lallerstedt co-founder of Black Market Watch a Switzerland-based non-profit group focusing on cross-border smuggling.

"It's not a strong federal state that can overrule its members" he said. "At the same time individual states have obligations to the EU. So you're in this sort of half-way house."

AP