The Maria Pia bridge: Eiffel's iron arch that took the railway into Porto

On Sunday 4 November 1877 Porto was so full that, one reporter wrote, many thousands slept in the street. The night train the evening before had brought what another paper called a real invasion of tourists. There was not a room left in any lodging house; in one, the servants gave their cubbyhole to four guests and slept on the landing.1 source1 source

At 11 in the morning the guests gathered at Devesas station in Vila Nova de Gaia, on the south bank of the Douro. Shortly after half past twelve a train of 24 carriages carrying more than 1,200 people pulled out towards the new iron bridge. Crowds lined the track. On the slopes of both banks, the Comércio do Porto reported, many tens of thousands of onlookers packed every rock and terrace, and the river below was covered with decorated boats.1 source1 source

King Luís I and Queen Maria Pia arrived on a royal train with the princes Carlos and Afonso, ministers and the diplomatic corps. In a pavilion facing the bridge the engineers were presented to them, the French builder Gustave Eiffel among them. The Bishop of Porto, Dom Américo, walked out to the middle of the arch and blessed it. Then the royal train crossed, and the fort on the Serra do Pilar fired a 21-gun salute.1 source1 source

A retrospective in the Jornal de Notícias 50 years later added two details. The engine, No. 17, took 55 seconds to cross. And Prince Carlos, the heir, and his uncle Infante Augusto stayed behind on the south bank until the royal train came back for them, so that if the first train fell into the river there would still be a king.1 source1 source

Portugal's first railway opened between Lisbon and Carregado in 1856. By 1864 the Northern Line, the Linha do Norte, had reached Gaia. Porto, the country's second city, sat on the cliffs opposite, and north of the river the state was building the Minho and Douro lines. Between the two networks lay a gorge more than 60 metres deep.2 sources2 sources

Closing that gap took 13 years of argument over the site of the Porto station, the line of the crossing and money, a story told in our article on the first railway. The line was run by the Companhia Real dos Caminhos de Ferro Portugueses, a private company run by a board in Lisbon and a committee in Paris. Its director general from 1872, the army engineer Manuel Afonso de Espregueira, settled the route. His engineer Pedro Inácio Lopes worked out the “Seminário line”, which crossed the river below the ruined seminary on the Porto bank.3 sources3 sources

A law of 26 February 1875 cleared the last obstacles. It exempted the company from a transit tax and let it build the bridges for a single track, ending a dispute that had run since the first railway contracts of the 1850s over whether every iron bridge had to be built for two.1 source1 source

The company invited tenders and set 1 May 1875 as the deadline. Four builders answered: G. Eiffel et Cie and two other large French firms, and one from England. Two more withdrew. Each proposed something different, and their prices ranged widely.2 sources2 sources

Before accepting so bold a design, the company had it checked in Paris by a commission of three engineers, Krantz, Molinos and Henri de Dion. De Dion tested the arch with a new method of calculation he had just presented to the Société des Ingénieurs Civils. The commission found the project well conceived and buildable, and concluded that the bridge, well made and carefully erected, would behave well.1 source1 source

In Lisbon the government's Junta Consultiva de Obras Públicas weighed suspension bridges, straight girders and arches. A suspension bridge would have needed towers about 70 metres high; a girder, two piers 56 metres tall. The Junta's rapporteur, João Crisóstomo de Abreu e Sousa, recommended Eiffel's arch and called it one of the best-studied projects ever put to the ministry. His one regret was that the deck had not been made wide enough for a road beside the track.1 source1 source

The contract went to Eiffel's firm on 22 June 1875, according to Infraestruturas de Portugal (IP), which owns the bridge today. The company's later minutes refer to a contract dated 22 July 1875; the first date is probably the award and the second the signature, but the sources do not say.2 sources2 sources

In 1875 Gustave Eiffel was 42 and not yet famous. He had set up his own works at Levallois-Perret, outside Paris, in 1867, and made his name with tall iron viaducts on French railways. The Douro was his firm's first great arch. In the spring of 1876 he moved to Portugal and lived at Barcelinhos, near Barcelos, while his firm also built bridges on the state's Minho line.3 sources3 sources

The arch itself was most likely drawn by Théophile Seyrig, Eiffel's partner, who ran the firm's design office. When Eiffel et Cie showed a model of the bridge at the Paris Universal Exhibition of 1878, its own notice said that the calculations and the design were by Seyrig and Henri de Dion, and that the works were carried out by Émile Nouguier, Joseph Collin and Angevère. Nouguier devised the method of erecting the arch. Seyrig described the bridge to the Société des Ingénieurs Civils in October 1878 without once naming Eiffel.3 sources3 sources

The two men soon fell out, and by 1880 Seyrig was designing for a rival firm the Ponte Luís I, downstream in Porto; we tell that story in our article on the Luís I bridge. José Manuel Lopes Cordeiro, a historian at the University of Minho, concludes that the Maria Pia was a collective work in which Eiffel directed the project, but that its new element, the great arch, was Seyrig's.2 sources2 sources

The arch is made of two latticed ribs that lean towards each other: 15 metres apart at the hinges on the banks and 3.95 metres apart at the crown. The lean steadies it against side winds. Each rib is deepest, about 10 metres, near the middle, where the bending is greatest, and tapers to a pin at each end. That gives the arch its crescent shape. The pins carry the thrust from trains and from changes of temperature into the abutments at fixed points, which also made the arch easier to calculate.2 sources2 sources

The deck is a lattice girder on wrought-iron piers, the tallest about 43 metres high. Near the crown it passes through the top of the arch rather than over it. An early draft had put the deck on top, as Eiffel later did at Garabit, but it was lowered to give the wind less to push on and the arch the greatest possible rise.2 sources2 sources

Work began on 5 January 1876. The masons built granite bases on the rock of both slopes, the iron piers went up on them, and the deck girders were assembled on each bank and pushed out over the piers, then beyond them into mid-air, as far as the points where short piers would later stand on the arch.2 sources2 sources

Then the arch began, on 2 March 1877, from both banks at once. It was divided into 21 segments. The first segments, next to the banks, were set on scaffolds on the rocks; after that there was nothing below but the river. Each new segment hung from steel-wire cables tied back to the deck on top of the main piers, and the number of cables grew with the weight to 16 for each half. The deck in turn was anchored to the rock on the Porto side and to a masonry block on the Gaia side.3 sources3 sources

The iron came up the river by boat. At the tip of each half, a timber crane hanging from a cable strung across the gorge between two 10-metre trestles lifted the pieces into place. Riveters followed on a hanging platform. The two halves met on 24 September 1877, according to the printed mount of a photograph album of the bridge made that year. A note in the company's archives, quoted in the Gazeta dos Caminhos de Ferro in 1956, puts the closing of the arch at ten past three on the afternoon of 28 October instead; the sources do not explain the difference. The piers on the arch went up next, and on 28 October the deck was run into its final position.2 sources2 sources

About 150 workers built the bridge in 22 months. Just before the deck was finished, Adelaide Lopes, the chief engineer's wife, insisted on being the first person to cross. On her husband's arm she walked over the unfinished deck, with no railings and the river 60 metres below, crossed the last gap along a bare girder, and then walked back, so that nobody coming from the Lisbon side could claim to have been first.3 sources3 sources

A commission of three Portuguese engineers tested the bridge from 31 October to 2 November. For the static tests it used two trains, each pulled by two 61-tonne Sharp engines from the Minho and Douro lines, then the heaviest in the country, with eight loaded wagons. They parked them on the whole arch, on each half in turn and on the centre. The crown sagged by no more than 20 millimetres. A goods train of 358 tonnes then crossed at 22 km/h and a lighter train at 31 km/h, the most the curves at either end allowed. Seyrig's own account, as summarised by Coste and Godart, instead gives a 355-tonne train at 31 km/h.3 sources3 sources

The commission's report said the arch was much stiffer than the bridge at St Louis on the Mississippi, the only one it thought comparable. IP and the American Society of Civil Engineers both describe the 160-metre span as the longest iron arch in the world when it opened.3 sources3 sources

While it was being built, the bridge was known as the “D. Fernando”. On the day of the inauguration it took the name of Queen Maria Pia of Savoy, the wife of Luís I. The company's board had asked her permission on 3 November, and on 15 November it recorded that, in all the company's acts, the Douro bridge would henceforth be called the “Ponte Maria Pia”.2 sources2 sources

On 5 November 1877 the first regular train ran through from Lisbon to Porto, and the last section of the Northern Line, from Gaia to Campanhã station in eastern Porto, was open. For the first time the capital and the second city were joined by rail without a change at the river, and the main line could meet the state's Minho and Douro lines on the north bank.2 sources2 sources

It was expensive. Pedro Inácio Lopes's account of the cost of finishing the line puts the bridge at 1,413,577 francs out of about 2.54 million for the whole section, which works out at roughly 752,000 francs per kilometre. Manuel de Azeredo, a Porto engineering professor who wrote a history of the city's bridges, gives 965,000 francs for the bridge. The sources do not say what each figure includes.2 sources2 sources

The American Society of Civil Engineers credits the bridge with establishing Eiffel as an important bridge designer. At the Paris Universal Exhibition of 1878 his firm won a grand prize for civil engineering for it. In June 1879 the French Minister of Public Works asked for the Garabit viaduct over the Truyère, a two-hinged arch of the same type spanning 165 metres, to be given to Eiffel without a tender. His decision gave the reason: it was Eiffel's Douro bridge that had given the state's engineers the idea for the new route.3 sources3 sources

For two decades every locomotive the company owned crossed the bridge without any speed limit, even as engines grew heavier. In 1891 and again in 1897 the government sent engineers to inspect it, because people in Porto feared that fumes from a nearby carbon disulphide works were eating the iron. A rumour spread that rotten rivets were raining from the bridge.1 source1 source

By 1899 some deck parts showed signs of fatigue. The company called in Maurice Koechlin, of Eiffel's works at Levallois-Perret, and on his advice replaced the deck floor and stringers and strengthened the cross-beams in 1899 and 1900. Its own ironworks at Ovar, set up to look after the bridge, replaced diagonals between 1901 and 1906 without stopping the trains. From then on the heaviest engines were kept off the bridge and speeds were cut, and further repairs followed in 1922 to 1926 and in 1951.2 sources2 sources

Restrictions kept the bridge safe but made it a choke point on the main line. In February 1981 the Council of Ministers called a new double-track bridge a priority that could not be put off. The old bridge, it said, was the only rail link to Porto and the north, and its single track and age limited loads, speeds, capacity and journey times. Strengthening it would not cure that and would spoil a monument that had to be preserved.1 source1 source

The replacement, the São João bridge designed by Edgar Cardoso, was built about 180 metres upstream: a double-track concrete frame with a central span of 250 metres between two piers founded in the river close to each bank. It opened on 24 June 1991, Porto's feast day of São João. That day the Maria Pia carried its last trains, after almost 114 years in service.3 sources3 sources

The bridge had already been honoured. A decree of 26 February 1982 classified it as a national monument; the government's 1981 resolution had already described it as declared a monument in 1976, and the sources do not explain the earlier date. In 1990 the American Society of Civil Engineers named it an International Historic Civil Engineering Landmark. IP, which owns it, says it carries out regular inspections and preventive maintenance.5 sources5 sources

Finding it a new job has proved harder. In 2004 a protocol was signed with the Porto and Gaia councils to turn it into a cycle path, at an estimated €1.5 million, but it was never carried out. In 2007 Refer, the state rail infrastructure company of the time, marked the bridge's 130th birthday by announcing €2 million to repaint it. In 2013 two architects even proposed moving it to a city block in Porto.1 source1 source

In March 2023 four Socialist MPs from Porto asked the government whether IP would reopen the bridge to walkers and cyclists. IP had said it would study that use with the two councils once Porto had converted the old Alfândega railway branch nearby for walking and cycling. Nineteen years after the cycle-path protocol, nothing had been built.1 source1 source

Its design lives on downstream. The Ponte Luís I, opened in 1886, is also an iron arch hinged at both ends, and was designed by the same man, Seyrig.3 sources3 sources