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London, the eponymous city in the Mortal Engines series, is a colossal, mobile metropolis that roams a post-apocalyptic world. Built on massive caterpillar tracks, London consumes smaller towns and cities for resources, leaving behind a trail of destruction. Its inhabitants, known as Londoners, live in a stratified society, with the wealthy elite residing in the upper levels and the working class toiling in the lower depths.