Megabridges: Spanning The Void is dedicated to a selection of spectacular and pioneering milestones in the art of engineering. This ranges from the Pont du Gard of Roman times to the French TGV high-speed train. The documentary looks at gigantic dams, navigable canals, kilometre-long tunnels that cross mountains and seas, and the Millau Viaduct, the longest cable-stayed bridge in the world. It provides insights into the construction and operation of these icons of progress.