The last time – it was around five years ago – I drove along the ‘Chemin des Dames’, on the high ridge overlooking Rheims, rusty old shells were still being piled at crossroads, where the local bomb-disposal squad would pick them up every fortnight or so like dustmen on their regular rounds. There were stories told, in cafés I drank in, of the odd tractor being blown up and of children playing in the limestone caves and being gassed to death when they accidentally kicked against phosgene bombs. It is the most terrifying old battlefield I know. During General Robert Nivelle’s disastrous offensive of 16 April 1917, French soldiers were mown down by hidden machine guns as they scrambled up that steep escarpment; fighting with hand-grenades and flame-throwers went on for days in the pitch darkness of the caves. The Chemin des Dames was, for the French, the turning point of the First World War. Mutiny followed, and the British took up the main burden of the Western Front – with their calamitous debut in Flanders that summer and autumn.