learning with fdq: world's tallest bridge

image from businessweek.com

usually when i see that fdq has recorded "megastructures" on tivo, i ignore it. but last night he made me watch parts of the episode featuring the millau viaduct, which is the world's tallest bridge. the designers wanted to make the bridge as non-obstrusive to the surrounding natural landscape, envisioning the piers as butterflies. they produced an amazing product! there's a good overview of the bridge at amazing nature blog entry or watch a clip from the show here.

fdq's question: why do they call it viaduct versus just a bridge?