The Tarn (; , , possibly meaning 'rapid' or 'walled in') is a long river in the administrative region of Occitania in southern France. It is a right tributary of the Garonne. The Tarn runs in a roughly westerly direction, from its source at an elevation of on Mont Lozère in the Cévennes mountains (part of the Massif Central), through the deep gorges and canyons of the Gorges du Tarn that cuts through the Causse du Larzac, to Moissac in Tarn-et-Garonne, where it joins the Garonne, downstream from the centre of town. Its basin covers approximately , and it has 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. Main tributaries The tributaries of the Tarn include: Agout (in Saint-Sulpice) Alrance Aveyron (near Montauban) Cernon Dourbie (in Millau) Dourdou de Camarès Jonte (in Le Rozier) Lemboulas Lumensonesque Muze Rance (near Trébas) Tarnon (in Florac) Tescou The Tarn separates the Narbonne and Aquitaine basins. Departments and cities The Tarn passes through the following departments and towns: Lozère: Le Pont-de-Montvert, Sainte-Enimie Aveyron: Millau Tarn: Albi, Gaillac, Lisle-sur-Tarn, Rabastens Haute-Garonne: Villemur-sur-Tarn Tarn-et-Garonne: Montauban, Moissac. 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 floods, which are the most dangerous in Europe along with the Danube. The floods of March 1930 saw the Tarn rise more than above its normal level in Montauban in just 24 hours, with a discharge of (the average discharge of the Rhine is ; the average discharge of the Nile during the traditional annual flooding before the building of the Aswan Dam was ; the average discharge of the Mississippi River is ). One third of the Tarn-et-Garonne department was flooded, about 300 people died, thousands of houses were destroyed, the low-lying districts of Montauban were destroyed, and the town of Moissac was almost entirely destroyed. Navigation The Tarn was once navigable from its junction with the Garonne to Corbarieu, near Montauban. This stretch of river included seven river locks over a distance of . The canal was linked to the Canal de Garonne in Moissac by a branch lock upstream of the first river lock, and again, via the Canal de Montech, at Montauban. The two access points from