‘I was born at the moment when the sun was setting on the Age of Reason.’ Appearing at the start of Arrow in the Blue, one of the memoirs that were his most lasting achievement, this judgement could have been made by any number of Arthur Koestler’s contemporaries. A sense of having entered the world at a point when it was descending into madness shaped his generation. Koestler and his contemporaries could not help seeing the break-up of Europe’s high bourgeois civilisation as a catastrophe. For nearly all of them, a breakdown of rationality defined the epoch. For many, communism was not so much an attack on Europe’s bourgeois civilisation as an attempt to renew it in a more durable form.

Marxism – a faith with all the trappings of reason – replaced the religion that had been lost, which was not Christianity or Judaism but the liberal faith in gradual progress. Captivated by a seemingly rational theory of history, converts to communism could imagine that the disasters that