Novelist John Lanchester, journalist Tim Marshall and historians David Frye and Kylie Murray join Anne McElvoy to discuss why we build walls rather than bridges and what it says about civilisations past, present and future from Persia to Berlin, the USA to a dystopian vision.

John Lanchester's latest novel is called The Wall. David Frye has written Walls: A History of Civilisation in Blood and Brick is out now Tim Marshall's book Divided: Why We're living in an Age of Walls is out now

Producer Jacqueline Smith