The Millau Viaduct (Viaduc de Millau) is a cable-stayed motorway bridge that carries the A75 autoroute across the valley of the River Tarn just west of Millau, in the Aveyron department of southern France. It is 2,460 metres (8,070 ft) long, and with a structural height of 343 metres (1,125 ft) from the foot of its tallest pier to the tip of the mast above it, it was the tallest bridge in the world for just over two decades, until late 2025. The French engineer Michel Virlogeux designed it with the British architect Norman Foster, and the Eiffage group built it for about €394 million, inaugurated on 14 December 2004 and opened to traffic two days later. It matters because it completed the A75 route between Clermont-Ferrand and Béziers, taking holiday traffic between Paris, the Mediterranean and Spain off the congested valley road through the town.
Seven concrete piers between the Causse Rouge and the Causse du Larzac
The viaduct does not descend into the valley at all. It runs from one limestone plateau to another: the Causse Rouge on the northern side and the Causse du Larzac on the southern side, both inside the Grands Causses regional natural park, on land belonging to the communes of Millau and Creissels. Between the two abutments, which anchor the deck to the plateaus, stand seven concrete piers numbered P1 to P7. Their heights follow the shape of the valley: pier P2, closest to the Tarn, rises 245 metres (804 ft) to the level of the roadway, P3 reaches 221 metres (725 ft), and P7, on the shoulder of the slope, is only 77 metres (253 ft). When the last piers were finished in November 2003, P2 and P3 were the two highest bridge piers in the world.
Each pier stands on four concrete shafts, each 15 metres (49 ft) deep and 5 metres (16 ft) in diameter, capped by a footing 3 to 5 metres thick. Work on the shafts began in the weeks after the first stone was laid on 14 December 2001. Once the piers emerged in March 2002, they climbed fast: sliding formwork supplied by PERI, held by anchor shoes and rails inside the shaft of each pier, let crews pour a new layer of concrete roughly every 20 minutes, and each pier grew by about 4 metres (13 ft) every three days.
A 36,000-tonne steel deck pushed out 600 millimetres at a time
On top of the piers runs a steel box-girder deck weighing around 36,000 tonnes. It is 32 metres (105 ft) wide and 4.2 metres thick, and it is divided into eight spans: six central spans of 342 metres (1,122 ft) and two end spans of 204 metres (669 ft). Its backbone is a line of 173 central box beams, each 4 metres across and 15 to 22 metres long, onto which the side floors and side box beams were welded. Seen from the side, the deck is shaped like an upside-down aircraft wing, so that a strong crosswind presses it down rather than lifting it. In plan the road is not straight but follows a gentle curve with a horizontal radius of 20 kilometres (12 mi).
Nobody lifted the deck into place with cranes. It was assembled on the two plateaus and launched horizontally out over the valley, the northern and southern halves advancing towards each other. Hydraulic jacks on each plateau pushed from behind. On top of every pier sat a computer-controlled pair of opposed hydraulic wedges, and eight temporary towers gave the deck extra support along the way. The lower wedge slid under the upper one to lift the deck, both moved forward together, then the lower wedge withdrew to set the deck down and the cycle repeated. Each cycle took roughly four minutes and moved the deck 600 millimetres (24 in). The two halves were a few centimetres apart on 28 May 2004 and were joined within a fortnight.
The steelwork was the responsibility of the Eiffel company, a link back to Gustave Eiffel, whose Garabit railway viaduct of 1884 crosses the Truyère gorge in the neighbouring Cantal department. The Belgian engineering firm Greisch of Liège designed the deck and its launching system and checked the structure against winds of up to 225 kilometres per hour (140 mph).
154 stays, 87-metre masts and the sensors inside pier P2
Once each half of the deck was in position, the steel masts were driven out along it lying flat, assembled, and then tilted upright in a single operation onto the pier below. Each of the seven masts is 87 metres (285 ft) tall and weighs about 700 tonnes. A single central plane of eleven pairs of cable stays fans down from each mast, 154 stays in all, so that every 342-metre span hangs from two masts. Depending on its length, a stay contains between 55 and 91 high-tensile strands, each strand made of seven steel wires and protected three times against corrosion: by galvanising, a coat of petroleum wax and an extruded polyethylene sheath. The outer casing of each stay is wrapped in a double helical strip, so that rain running down it in high wind cannot set the cable vibrating. The stays were installed and tensioned by Freyssinet, a subsidiary of the rival Vinci group and the only major firm on site from outside Eiffage.
The bridge is also a large instrument. Anemometers, accelerometers, inclinometers and temperature sensors are spread across the deck, piers, masts and stays. Pier P2, the tallest and therefore the most heavily stressed, has twelve fibre-optic extensometers in its base that detect movements of around a micrometre, and electrical extensometers at the tops of P2 and P7 can take up to 100 readings a second during storms. Two piezoelectric sensors weigh passing vehicles and sort them into fourteen types. The data travels over an Ethernet network to the management building beside the toll plaza.
Why the A75 left the Tarn valley floor at Millau
The bridge exists because of the shape of the land. The A75, known as la Méridienne, crosses the Massif Central from Clermont-Ferrand to Béziers, and together with the A71 and A10 it forms a direct route south from Paris to Languedoc and on to Spain. The Tarn has cut a deep valley between the high plateaus of the Grands Causses, and before 2004 the motorway stopped on either side of it. Drivers had to descend into the valley and pass through Millau on the old national road, the N9. By the 1980s the result was long queues at the start and end of every July and August holiday season.
Four corridors were studied. A Great Eastern route would have crossed both the Tarn and the Dourbie on two very long, very high bridges, and served Millau badly. A Great Western route along the Cernon valley was 12 kilometres longer and would have cut close to the villages of Peyre and Saint-Georges-de-Luzençon. A route near the N9 clashed with existing buildings. The intermediate route just west of the town, favoured locally, was chosen by ministerial decree on 28 June 1989. A low version, dropping into the valley and crossing the river on a short bridge before tunnelling into the Larzac, was rejected because it would have cut into the water table and cost more. A decree of 29 October 1991 fixed the high solution: one structure of around 2,500 metres, more than 200 metres above the river.
A design competition followed. On 15 July 1996 the public works minister Bernard Pons announced that a jury chaired by the highways director Christian Leyrit had chosen a multi-span cable-stayed design from the engineering group Sogelerg, Europe Etudes Gecti and Serf with Foster + Partners. Wind-tunnel tests then reshaped the deck. The construction contract went to Eiffage, which set up the Compagnie Eiffage du Viaduc de Millau in March 2001 and won the concession that August: Eiffage paid for the bridge in return for the right to collect tolls for 75 years, until 2080, although the state can take it back as early as 2044 if revenue runs high. Groups including WWF and France Nature Environnement opposed the project, arguing that a cheaper western route existed, that tolls would keep traffic in the valley and that the piers would sit on weak shale.
What the viaduct changed for Millau, Creissels and the Grands Causses
The bridge opened on 16 December 2004, ahead of the planned date of 10 January 2005. It is the one tolled section of the 340 kilometres (210 mi) of A75 between Clermont-Ferrand and Béziers; as of 2025 a car paid €11.20, rising to €13.90 between 15 June and 15 September. Estimates put daily traffic at between 10,000 and 25,000 vehicles. The toll plaza, a few kilometres north of the bridge, has sixteen lanes under a 100-metre leaf-shaped canopy made of 53 segments of ceracem concrete, and cost a further €20 million.
For Millau itself, the change was the end of the summer jams on the N9 and a new kind of visitor: people who come to look at the bridge rather than drive through the town. Soon after opening, cars were stopping on the hard shoulder for photographs, and the speed limit on the deck was cut from 130 to 110 kilometres per hour. A rest area, the Aire du Viaduc de Millau, was built around the old Brocuéjouls farm just north of the bridge and opened on 30 June 2006 at a cost of €5.8 million. In December 2004, before the opening, 19,000 walkers crossed part of the deck, and on 13 May 2007 a race of 10,496 runners started in the Place de Mandarous in central Millau and crossed the viaduct and back over 23.7 kilometres. In 2006 the International Association for Bridge and Structural Engineering gave the viaduct its Outstanding Structure Award.
The builders expect the structure to last at least 120 years. For how the Tarn valley, the causses and the Massif Central fit into the wider landscape, see our guide to the geography of France, and for a crossing built across a southern French valley some two thousand years earlier, read about the Roman aqueduct bridge of the Pont du Gard.