Ursula LeGuin’s outstanding novel The Dispossessed begins with the simple line ‘There was a wall.’ It is a setup to a binary exploration of us and other, rich and poor, anarchist and industrialist, on two different planets, Urras and Anarres. Walls are physical structures just as they are dividing lines; LeGuin’s wall was of ‘uncut rocks roughly mortared.’ Others are literal blocking mechanisms, such as the walls of prisons, to keep people in, and the walls of old towns, to keep people out. Still others are borders, political objects designed to designate territory and zones of control. These are man-made impositions on the earth, statements in technology announcing our collective will.

Border walls have an effect on people. They are liminal places (for they invariably occupy space other than their geometric two dimensional line), with law on one side and disorder on the other, wealth on one side and poverty on the other, freedom on one side, and deprivation on the other. To pass from one side to another is often either an escape, an elevation, a salvation, or its opposite: demotion, relegation, failure. In that liminal space there is simultaneously a transient, human shriek of mortal power, sounded from the good side, from the builder of the wall: this land is my land.

Today, we hear cries of ‘Build That Wall‘ at Donald Trump rallies; the Israeli Segregation Wall in the West Bank divides that space for over seven hundred kilometres; the Berlin Wall and countless others in history hardened divisions between people, who would be unseen and unheard, denied communion with others. Yet around these spaces the world denies division. birds fly overhead, while moles and rabbits tunnel underneath. Plants and trees grow on either side, and in places where rivers form borders, such as the Rio Grande, no wall is possible, such is the power of nature.

There are changes that happen. Biodiversity is compromised by large walls, just as it is compromised by large urban centres. Countless studies have shown how animal ranges are restricted, which has knock on effects on things like seed distribution and other ecological systems. Walls are edge spaces, and the detritus of civilisations gets pushed to the edge – so rubbish and waste often accumulates, while the indigent and homeless sometimes find unwanted spaces near these walls. New ecosystems emerge, as the walls become less the end of something, and just a part of something different.

In time, of course, walls come down. Erosion, earthquakes, bombs, and politics can each play a role, but time ultimately undermines the foundations of every wall, just as it has done every civilisation of the past, and will surely do the same to our own. Just like us, walls are temporary things, while our Universe will persist.