‘The most bloodthirsty line in the French national anthem was written with the English in mind,’ David Bell wrote in the LRB in 1998. Claude-Joseph Rouget de Lisle, the military engineer who composed the words to the ‘Marseillaise’ in 1792, took the line about watering furrows with ‘sang impur’ from a poem which was much more specific about whose impure blood it should be.