NEXT time you are in Catalonia, and want to understand what the Schengen Area is all about, you could do worse than visit the Walter Benjamin memorial at the border village of Portbou in the Pyrenees. Benjamin was a Jewish philosopher and art critic who committed suicide while trying to escape from Nazi-occupied France during the Second World War.

The memorial, The Passage, by the Israeli artist Dani Karavan, is a chilling experience in itself. A rusty tunnel conceals a flight of steps that pitch down the mountainside to the rocks and sea from which you are protected only by a wall of unbreakable glass. You go down these steps as far as you dare and experience for yourself something of the precarious isolation and fear of exile.

Nearby you can visit the very railway station where the Nazis interrogated and murdered refugees like Benjamin – which is why he killed himself first. The Portbou memorial was financed jointly by the Spanish, German and Israeli governments to commemorate Benjamin's death. It was opened in 1995 just as the Schengen Area of free movement was being established across Europe.

Never again. Never more the helmeted border guards with their guns and suspicious faces. The tense moment when you hand over your documents. The click of the safety catch. Well, until now.

It seems that the borders are going back up across Europe to keep out refugees and terrorists. In the wake of the Paris attacks there is a clamour for the free movement between the 26 countries of the Schengen no-passport zone to be suspended.

Hungary has erected a 100-mile barbed wire fence. Sweden and Germany have restored temporary border controls. Travellers to Schengen itself, which is in Luxembourg, faced huge queues last week because of French border checks.

Britain is one of the few countries who've opted out of Schengen and is saying, in effect: told you so. John Reid, the former Labour defence secretary, dismissed Schengen, revealingly, on BBC's Today programme: “It's not an iron curtain, nor a ring of steel, it's a sieve.” Most of us would surely prefer a sieve to the Berlin Wall.

Free movement is one of the great achievements, not just of the European Union, but of European civilisation. Even non-EU countries like Switzerland and Norway are part of Schengen. Mainland Europe has become one country with a common visa. You only need to reflect for a moment on conflicts of the 20th century to understand the significance of this.

Towards the end of the Spanish Civil War, in 1938, half a million Republicans escaped to France over the Pyrenees via Portbou, pursued by Franco's fascists. Many were shamefully incarcerated in what were effectively concentration camps in south-western France. Only three years later, after France had fallen to the Nazis, many of these same refugees were escaping back over the Pyrenees along with Jews escaping anti-Semitic persecution by the Nazis.

Now, in Britain we find all this very hard to comprehend. This country hasn't been under foreign occupation since the Middle Ages and we have little conception of how borders figure in the minds of people who have lost their lives simply for crossing them. Yet for most Europeans, this is all within living memory.

And the fact that you have been able, because of Schengen, to drive across these European borders, between France, Germany, Belgium, Italy in an instant, without let or hindrance, is almost miraculous. And it is unbearably poignant when you consider what lives were lost in defence of these arbitrary geographical divisions.

It's the same when you cross from France to Germany across the oft-disputed region of Alsace Lorraine, which has been fought over since the dawn of the Holy Roman Empire. In Europe today it is possible to cross half-a-dozen national boundaries and language zones in a day and visit the same number of war cemeteries.

Now, we are told that the threat from a handful of Islamic militants has made Schengen unsustainable. We can't have the luxury of free movement when facing this “existential threat”. France is now “at war”. Last week a British newspaper printed a cartoon that appeared to compare Syrian refugees to rats crossing the borders of Europe.

It seems almost inconceivable that Europe could default back to the divisive borderlands of the 20th century. Most Europeans under the age of 40 can barely remember what it meant to have borders between all these countries. How did people move about? Go on holiday? Get to work?

The reality is that they didn't. Borders are primarily about containment and keeping out foreigners and alien ideas – they are as much psychological constructs as geographical ones. They define a defensive and essentially Mediaeval state of mind in which humanity is defined by mutual antagonism rather than co-operation.

This is the mind, indeed, of Islamic State, which is trying to roll back centuries of rational humanism. And that is why the borders must remain open in Europe.

Islamic State is not an existential threat, and bears no comparison to the genuine threats that faced Europe in the last century. Fascism was an existential threat; the Warsaw Pact was an existential threat. As recently as the 1980s a land war in Europe between the Soviet Union and Nato seemed a very real possibility.

It was Winston Churchill who said that an “Iron Curtain” had been drawn through the centre of the sub-continent by the Cold War. To even suggest that we should erect another one to keep out a handful of deluded bomb-throwers is an insult to the millions who died in the age of totalitarianism. Worse, it flatters the vanity of the bearded clowns waving their Kalashnikovs for the cameras.

IS claim to be a state but they don't have an army. They have no divisions, no air power, no tanks. The death they inflicted in Paris was an atrocity, and demands a response, but it has nothing to do with international war.

So, there is no real reason why Europe's internal borders should be restored. It is anyway naïve to believe that border posts provide security. Abdelhamid Abaaoud, who is thought to have been an organiser of the Paris killings, was a Belgian national and grew up in Molenbeek, a district of Brussels.

Terrorists don't recognise borders at the best of times and they will always find ways of getting through. The Atlantic Ocean is the greatest border on the planet yet al-Qaeda still managed to strike New York's twin towers.

There have been exceptional circumstances because of the influx of mainly Syrian refugees into the EU. It was inevitable that terrorists would try to exploit the confusion to infiltrate Europe. But we have to hope and assume that the civil war in Syria will end eventually, and that North Africa and the Middle East will return to something like normality.

The danger is that European governments in their desperation to be seen to be “doing something” will destroy what they should be trying to defend: freedom itself. That's what the Schengen area is really all about. It is an expression of personal liberation which defines the modern age.

The Paris attack was comparable to a serious air accident – a shocking event, certainly, but not something that would make us end free movement in the skies. We must not allow a handful of terrorists to end free movement on the land.