Humanity had to wait until the Bronze Age, around 3,500 years ago, to witness the invention of the wheel in ancient Mesopotamia. This might come as a surprising fact considering how important the wheel is for the transportation of food, commodities, and eventually people.

Copper and other materials were used to build the wheel axles. The wheel-and-axle concept was simply genius, and the axle had to be of perfect diameter to create a nice balance between friction and load support. Smoothness and roundness were also very important for the wheel to turn. All these components are so inter-connected and complex that many anthropologists suggest that the wheel could not have been invented in phases. It must have been created all at once.