Eight hundred years ago, the biggest building boom the world had ever seen exploded across Europe. All over the continent rival towns and cities competed with each other to build vast cathedrals that towered higher than any other buildings in Europe. But this craze for Gothic architecture also called for the development of a machine that could raise enormous quantities of stone to extreme heights. A handful of medieval illustrations show a type of giant crane, perched high on the top of these gothic buildings. Powered by people walking inside a large treadwheel, just how did medieval craftsmen build such cranes? This programme attempts to reconstruct the medieval cathedral crane using traditional methods, but not everything goes according to plan.