Visiting the actor Simon Gleeson in 2014 a few months after he was cast as Jean Valjean in a new production of Les Misérables, I was startled by the bulked-up friend who met me from the train. ‘What the hell?’ I asked. ‘I have to lift a cart,’ he replied. It is not a bad exegesis of Victor Hugo’s sprawling novel and the musical it gave rise to. And it is an anecdote that would probably delight David Bellos. ‘Muscular strength,’ Bellos writes of Valjean, ‘acrobatic skills learned in prison and an ability to tolerate pain allow him to release Fauchelevent from under his cart, to climb the convent wall, to escape from the hold-up and to carry Marius through the sewers.’ Each of these events is pivotal to Hugo’s story (though there is no episode at the convent wall in the musical) and requires of Valjean the sort of muscularity that is immediately evident to both readers and audiences – hence Simon’s physical transformation.