They seem to be the tallest thing around, so what put them up?
They are self-elevating. They jack themselves up. It was the invention of the self-elevating crane and the self service elevator which made popular tall buildings. In older cities, such as Paris, the height of a building was limits by the number of flights of stairs people were willing to climb.
Large cranes are built in sections imagine like an erector set. When there is a large building to be built the crane arrives in smaller easier to manage pieces and assembled on site.
