In the mid-1950s, when I was studying Chinese and Chinese history at Columbia University, professors had ground-floor offices. But upstairs, where the toilets were, we occasionally glimpsed an elderly man who slipped quickly out of sight. This apparition, rarely mentioned by our teachers, was Karl August Wittfogel, a German ex-Marxist (or perhaps ex-communist), now very anti-Mao, which in those days most China scholars weren’t. In his book Oriental Despotism – not on our reading lists – Wittfogel put forward the ‘hydraulic state’ theory of Chinese history, which held that imperial control in China lay in its management of water – rivers, irrigation and dams – and that disorder usually arose from individuals who fought either the emperor or each other over water control, or from rebels who emerged because of droughts or bad management of floods.

In his ‘secret history’, which reveals no secret, Philip Ball, whose previous books had nothing to do with China, seems at first to disdain Wittfogel’s hydraulic thesis. But then he declares: ‘Wittfogel’s thesis has never quite gone away, and this is surely because it acknowledges one indisputable fact about statecraft