When there is a will to migrate, there is often a wall to stop it. After increasing numbers of migrants tried to breach Spain’s enclaves in northern Africa in the 90s, the Spanish built a fence to block their path. Last year Bulgaria built another on its border with Turkey. And this summer, Hungary has followed suit – starting work on a fence that will supposedly separate it from Serbia, its southern neighbour.

But where there is a wall, there is most often a way to get around it. Spain did not stop at just the one fence. It was forced to build a second – and then a third. Only then did the fence begin to keep people out in the way its builders had initially hoped. And even after that, migration to Europe was simply achieved through other routes – first through Libya, and now via Turkey.

The new fences at Calais already seem to constitute a similarly futile game. It is widely reported that while attempts to breach Calais’s defences have decreased, migrants are attempting to reach England from other ports including Dunkirk in France, and others in Belgium and Holland. The British government enjoys using the language of floods and swarms to describe the situation, so they will eventually appreciate that when a river bursts its banks, there is only so much water that the levee can hold back.

Bulgaria’s fence has had a similarly limited effect. Today, if you head to the Balkans, you’ll meet plenty of mainly Afghan migrants walking north to Scandinavia, having successfully crossed the Turkish-Bulgarian border.

The wall simply constitutes a mental blockage, rather than a physical one

It seems naive to expect a different fate to befall Hungary’s wall, the site of which those same migrants will shortly reach. At its most effective (from a Hungarian point of view), the thousands of migrants heading up from Greece and Bulgaria will simply make their way through Croatia or another neighbouring country. At its most pointless, the wall simply acts as a public relations exercise aimed at the Hungarian public, rather than at foreigners.

That certainly seems to be its current role. The latest reports suggest that very little of the fence has actually been built – and that nothing is yet blocking the well-known crossing points. As a result the wall simply constitutes a mental blockage, rather than a physical one. It creates the illusion for a domestic audience that something is being done about migration, even when it isn’t – and even when it can’t. It maintains the logical fallacy that a migration crisis of this magnitude can be ended with short-term measures like fences – even when the forces that are driving people towards such obstacles are far more frightening than a fence will ever be.

As I write this, I am watching pick-up truck after pick-up truck drive hundreds of migrants along one of the two main people-smuggling routes through the Sahara into Libya. Almost none of the people braving this trek will enter the EU via Hungary. But most of them may land in Italy, and only a few of them may later reach the new fences at Calais. It is inconceivable that a slender fence will stop people who will soon cross the Mediterranean, and the Libyan civil war. Not to mention this three-day slog through the Sahara, which has killed hundreds if not thousands in recent years. And which some believe is more dangerous than the sea itself.