Richard Hammond reveals the engineering inspirations behind the tallest road bridge in the world: the Millau Viaduct in France. He fires three quarters of a million volts from his finger tips to see how the power of lightning cut the steel structure quickly and accurately. The huge piers – 340 metres high, and which would look down on the Eiffel Tower – were positioned to millimetre accuracy with the system that located lost nuclear submarines. The longest road-deck in the world was launched along the top of the piers and required the slipperiest substance known to man – Teflon. Not even a gecko can stick to it. Steel cables hold the bridge in shape, born of a series of mining accidents. And to allow the bridge to expand a metre and a half in the summer sun, the engineers turned to an ancient Celtic boat-building technique which can make concrete as bendy as wood.