Mankind’s greatest invention, they say, is the wheel. It’s certainly hard to argue with that. But what would take second place? Perhaps the humble brick would be one of the contenders. So small that it fits in the hand, but when put together with lots of other bricks, so large that it can create a structure visible from space. Admitted, not all parts of the Great Wall of China are made from fired clay, but much of it is, in particular the crowns.