People have come up with the idea of the wheel many times and in different places, but what were the key turning points which led to mass transport and the miracle of modern logistics? Bridget Kendall discusses the still-unfolding story of the wheel with historian Richard Bulliet, logistics expert Jagjit Singh Srai and Cyr wheel dancer Valerie Inertie.
(Photo: Wagon wheels and the view of Monument Valley in Utah, USA)