‘Great edifices, like great mountains, are the work of centuries,’ wrote Victor Hugo in Notre-Dame de Paris. ‘The man, the artist, the individual, is effaced in these great masses, which lack the name of their author. Human intelligence is there summed up and totalised.’ The foundation stone of the cathedral of Our Lady of Paris was laid 850 years ago, but it was the work of generations, and took 200 years to complete.