The writer Rory Maclean, whose literary travels through the post-1989 former Soviet bloc deserve a place on any serious bookshelf, came up recently with an arresting statistic. In that memorable year three decades ago when the Berlin Wall fell, there were 11 countries in the world that felt the need of any sort of border fence or wall. Today, there are more than 70.
Has the world become a more predatory place in those 30 years? It hardly seems so; and even if it has, most of the more obvious jeopardies now posed to national security are of types – cybernetic, corporate, economic – that all the breeze blocks and razor wire in the world can do little to repel.
So have we, then, become more fearful and paranoid about our neighbours? Evidently we have, as witness the past half-decade's upsurge in tub-thumping, flag-waving protectionism, from Trump to Farage to Putin. And yet the flow of technological and geopolitical change would seem to point in the opposite direction: towards enhanced understanding, dialogue and trade among peoples previously shut off from one another by Cold War enmities and primitive communications, rather than towards the drum-brained belief that the less you have to do with foreigners the better.
It is all very perplexing, until one remembers that the view from Brexit Britain and its chosen mentor, Trump's USA, is not the only truth on offer. There are swathes of the world where the trend is indeed towards a more relaxed, constructive co-habitation with neighbours and counterparts, and where concepts like 'abroad' or 'foreign' have come to mean progressively less rather than more.
You could point, for example, to some of sub-Saharan Africa, or to the Pacific Rim. But the most compelling example lies closer to home, with the inconveniently united 27 EU partners on whom Britain is turning its back: and particularly the 22 that form the Schengen Area (opt-outs were secured by Ireland and Guess Who, while the other four EU members are committed to future accession). The European Free Trade Association (EFTA) countries (Iceland, Liechtenstein, Norway and Switzerland) are associate Schengen members, and the Ruritanian trio of Monaco, San Marino and the Vatican de facto Schengen states.
For those prone to equate co-operation with surrender, the 1985 Schengen Agreement is right up there with Vichy France. Its signatories are committed to lower their frontiers with one another by scrapping passport controls, visa restrictions and checks on cross-border commerce, in favour of a common external frontier. Britain, predictably, wanted none of it. That noise you can hear is Jacob Rees-Mogg cabling the Admiralty to make sure there's a gunboat on stand-by, just in case.
He would do better – we all would – to take pause and consider just what a remarkable achievement Schengen has been, especially given that it launched into an era of exceptional migration, political turmoil and financial adversity. Despite all that, governments representing more than 400 million people spread across 1.7 million square miles have agreed, and managed, to trust one another.
Schengen borders are frictionlessly crossed by 1.3 billion people every year, including 1.7 million daily commuters, and by €2.8 trillion of goods. The cost of trade has fallen by up to 1.6%. It is all underpinned by enhanced police co-operation and intelligence-sharing among member states. But the bigger reason it has survived is that it is very popular.
My wife and I just experienced its pleasures at first hand, visiting the Italian city of Bologna on a short city break from our home in Montpellier, south-west France. If there is one thing on which all of us can agree, it is surely that mass budget travel, airport commercialisation, and degrading security procedures have turned aviation from a luxuriant privilege into a dehumanising ordeal. Membership of the Schengen Zone does not remove those stresses, but it does spare you some of the others, notably passport checks and customs channels. If that doesn't strike you as a blessing, then you haven't shuffled through the cattle runs of Edinburgh Airport's passport hall on a night when the isometric scanners are playing up and two international flights have landed at once.
Driving across a Schengen border is even better: in most places, you won't even need to shift down a gear. Trains no longer sit for an eternity in border stations while backpackers scrabble for their passports. Of course, in most of the Schengen area there is no need for costly and tiresome transactions at the bureau de change. Our French Euros and credit cards were as valid in Italy as in France: one more tedious chore that need no longer intrude on the precious leisure of a short break.
What is harder to quantify, but at least as important, is the extent to which a Schengen attitude has developed. Italians or Germans, or the French or Dutch, are not just welcome in one another's countries. They are barely noticed. If you can wander freely from one nation to another, use the same money, deal with many of the same institutions and, by and large, find enough scraps of common language for routine conversation, then the whole spiky business of national distinctions rapidly diminishes. Local cultural curiosities remain beguiling, but now you can enjoy them without the nagging unease of being in an alien place where, sooner or later, you're likely to come a cropper.
Let's not be too utopian: any airport worth its salt can still find ways to make you miserable, and some would say that we all travel too much anyway for the good of the planet. But neither should we miss the significance of Schengen operating so smoothly between, say, France and Italy.
Aside from anything else, Bologna's council has legalised 'light' cannabis, and shops with names like Baked Bologna offer products that our local boulangerie does not stock. More generally, these are countries whose industries compete aggressively with one another, whose elective politics have headed in very different directions over the last few years, and which have felt the strain of the wretched refugee traffic from the Middle East and North Africa. Both are on standing alert against a terrorist threat. That they are comfortable enough with each other to go without a hard border is surely a triumph in a baleful, edgy, suspicious world.
This sort of visit reminds you too that there is a tangible value to the EU citizenship of which we Brits are to be so rudely stripped because some people in England don't like foreigners. The casual bonhomie with which the Bolognese mingle with the French, Germans and Spaniards who come to enjoy their city's medieval arcades and sumptuous cuisine is more than just shrewd hospitality. It is the easy, relaxed pleasure of people with things in common.
To amble freely between fine old cities like Montpellier and Bologna with the very minimum of bureaucratic interference and fuss simply feels – I can think of no better word – civilised. More civilised, certainly, than any wall: be it physical or metaphorical. It also feels like the future. Walls feel like the past.