Tarn (river) a mean flow of approximately . The Millau Viaduct spans the valley of the Tarn near Millau, and is now one of the area's most popular attractions. The tributaries of the Tarn include: The Tarn separates the Narbonne and Aquitaine basins. The Tarn passes through the following departments and towns: The Millau Viaduct, the tallest bridge in the world, carrying the A75 autoroute across the Tarn Gorge near Millau, opened in December 2004. The Tarn is famous for its brutal floodings, which are the most dangerous in Europe along with the Danube. The flooding of March 1930 saw the Tarn
Millau Viaduct speed of construction then rapidly increased. Every three days, each pylon increased in height by . This performance was mainly due to sliding shuttering. Thanks to a system of shoe anchorages and fixed rails in the heart of the pylons, a new layer of concrete could be poured every 20 minutes. The bridge road deck was constructed on land at the ends of the Viaduct, and rolled lengthwise from one pylon to the next, with eight temporary towers providing additional support. The movement was accomplished by a computer-controlled system of pairs of wedges under the deck; the upper and lower