The first cable-stayed bridge to top 500 metres, the Duge Bridge stretches 1.3 km across the valley, with its road deck up to 565 m above the river. Five times loftier than Brunel's iconic Clifton Suspension Bridge in Bristol, it is today the world's highest bridge. When designing a bridge, engineers must keep in mind three things: purpose, materials and form. A bridge's purpose is simply its function in the world - the gap it needs to cover. The materials are the building blocks of its construction, and its form is the specific design chosen by the engineer. A successful bridge is one whose design, form, construction and materials enable it to perform its primary function.