The Ponte Pênsil: Porto's first fixed bridge over the Douro, 1843

On Saturday 15 October 1842 much of Porto came down to the river. Between two pairs of stone obelisks, one on each bank of the Douro, a road of timber now hung from iron cables. The weather was mild, and ladies in their finery strolled out over the rushing water. Amid the bang of countless fireworks, the crowd cheered the master of the works by name.2 sources2 sources

That was the party, but regular service came later. According to Pinho Leal's dictionary of the 1870s, on 4 January 1843 the builders lined both sides of the deck with pipas, large casks, full of water, and left the load on it for sixteen hours. Nobody noticed the slightest change. On 17 February 1843 the bridge was opened “definitively” to public service.1 source1 source

That same night, 17 to 18 February, the Douro rose suddenly and flooded the Praça da Ribeira, the riverside square at the foot of the old town. A second flood followed about a week later, and by 28 February the water stood only three palmos, about 66 centimetres, below the great flood of 1823.1 source1 source

The paper added that people complained the ramp had been built of stones that were too small, although the government had given eight contos de réis, 8 million réis, towards it. The reports mention no damage to the bridge itself, which stood on rock chosen because it rose above the highest floods. Unlike the bridge of boats, it did not have to be taken apart when the river rose, so Porto and Vila Nova de Gaia, on the south bank, were no longer cut off by every flood.3 sources3 sources

Porto stands on the north bank of the Douro and Vila Nova de Gaia on the south bank, facing each other across a river with steep, rocky sides. For most of their history the two towns were joined by boats, and from 1744 by a regular ferry.1 source1 source

On 15 August 1806 the government opened a bridge of boats: about 20 boats moored side by side and tied with iron cables, with a wooden roadway on top for people, animals and carts. It rose and fell with the tide and could be opened to let larger ships through. On 29 March 1809, as French troops under Marshal Soult stormed Porto, crowds fleeing across it fell into the river through a gap in the middle, and thousands drowned.3 sources3 sources

The French destroyed the bridge on the night of 11 to 12 May 1809 to stop Arthur Wellesley's Anglo-Portuguese army from crossing. Manuel de Azeredo, a professor in the University of Porto's engineering faculty who wrote a history of the city's bridges, says they burned it; the British historian Charles Oman says they blew it up. Two improved bridges of boats followed. Both had the same weakness: the Douro floods hard and fast, and every year the bridge had to be taken apart more than once so the current would not carry it off. Each time, the two banks were cut off again.3 sources3 sources

The government's answer came in 1837. It signed a contract with the French contractor Claranges Lucotte, whom later sources call the Count of Claranges Lucotte, to build the main road from Lisbon to Porto and a bridge over the Douro at Porto “on the system of suspension in iron”. The contract was approved by a law of 7 April 1837 and sealed by deed on 5 May. In return the company would collect the tolls on the bridge.2 sources2 sources

Work did not begin until 1841. The first design, by the engineers Mellet and Bigot, would have carried Rua de São João, a street running down to the river, straight across to the main street of Gaia. It was not built. Another of Bigot's designs, from the Praça de São João Novo across to Gaia, had two spans of 120 metres and “a great triumphal arch in the middle of the river”. That was abandoned too.2 sources2 sources

The site was settled by Luís da Silveira Mouzinho de Albuquerque, inspector general of public works, who agreed to a crossing about 80 metres upstream of the bridge of boats. It was off to one side of the places the bridge had to serve. Its advantage was that two rocky knolls, one on each bank, rose above the level of the highest floods.2 sources2 sources

Bigot, a French civil engineer, designed the bridge and published a 23-page account of the works in French, Pont suspendu de Porto, printed in Lisbon in 1843. Manuel Bernardes Branco's 1879 summary of that report names Amédée Carruette as the other engineer. Some later accounts, such as Grace's Guide, also name the Portuguese engineer José Vitorino Damásio as co-designer, but the summaries of Bigot's report do not. Bigot is not mentioned in the French literature on suspension bridges, but Azeredo thinks he must have known the work of Marc Seguin closely. Seguin and his brothers are thought to have built several dozen suspension bridges, and their bridge at Tournon, on the Rhône, built in the 1820s and rebuilt in 1847, had much the same structure as Porto's, though with two spans.3 sources3 sources

For a span of 170 metres, a suspension bridge was still a fairly new idea. The first permanent ones, in eighteenth-century England and then in the United States, hung from iron chains, and a single bad link could bring one down. Seguin preferred cables of parallel iron wires bound together at intervals: if one wire broke, the cable lost only the load that wire carried. In Azeredo's list of earlier bridges, only a few had longer spans than Porto's, the longest of them in Switzerland.1 source1 source

Work began with a ceremony attended by the Porto authorities on 2 May 1841, the date in Bigot's report and in Pinho Leal; Azeredo's technical table gives 2 February 1841. Masons built four obelisks of dressed stone, two on each bank, each 18 metres tall. The cables were made in a yard set up for the purpose on the beach at Miragaia, about a kilometre downstream.3 sources3 sources

The materials came from several countries. According to Bigot, most of the iron castings came from England, with extras cast by Hargreave and Company in Porto; the forgings were made locally from Norwegian iron; and the wire came from Besançon, in eastern France.1 source1 source

At Miragaia the wire was drawn through a boiler of hot coal-tar oil to coat it, hung up to dry and then laid out on trestles. It ran in one continuous length, looping round at each end, so that each finished cable ended in an eye. The wire often had flaws, which the workers found by running it between their fingers, and every splice was tested with a lever. Bigot wrote that two men pulling together sometimes forced a splice until the wire snapped, and it broke on one side of the joint or the other.1 source1 source

Each of the eight cables, four on each side, was a bundle of 400 parallel iron wires 3.2 millimetres thick, tied at intervals with finer wire, according to Bigot's report as summarised by Azeredo. Pinho Leal's dictionary of the 1870s gives 220 wires and says each cable weighed 6,000 kilograms. The cables passed through windows just below the tops of the obelisks, resting on cast-iron rollers that let them move a little, and were then anchored to 32 iron ties sunk in vertical shafts cut into the rock.3 sources3 sources

The deck was timber, 6 metres wide, with a footpath one metre wide on each side, about 10 metres above the water. Its railings were lengths of square oak 1.5 metres long, set crosswise and nailed to the floor. An iron band joining the tops of the obelisks carried the words “D. Maria II, 1842”, after Queen Maria II, and small cast-iron plates gave the names of the engineers and the contractors.2 sources2 sources

On top, each obelisk had a Doric capital carrying a bronze ball 1.1 metres across. At the Porto end a house was built between the two obelisks, its facade closing the end of the bridge, for the men who ran it. Traffic did not drive straight on. It came up a ramp along the bank from the Ribeira, past a small booth where the toll was paid. At the Gaia end the road ran straight onto the deck.3 sources3 sources

The bridge was a business. Because a company had built it, the company kept what travellers paid to cross. According to Pinho Leal, quoting the Diário Ilustrado, a person on foot paid 5 réis, a horse 20 réis and a carriage 200 réis, and every rate doubled at night.1 source1 source

The concession ran for more than three decades. Pinho Leal says it ended in 1876, when the government took over the bridge; Azeredo dates the end to 17 January 1877.2 sources2 sources

Pinho Leal, writing in the 1870s, found it handsome and elegant, and recommended the view from the middle of the bridge, up or down the river.1 source1 source

From early on, people did not quite trust it. Some writers said the bridge trembled “like green twigs”, a Portuguese phrase for shaking with fear, when people walked over it. Bigot reported the opposite: in his tests, groups of 40 to 50 people marching across caused no oscillation worth noting.2 sources2 sources

Then two French bridges of the same type failed. On 16 April 1850, in a strong wind, the suspension bridge at Angers collapsed as a battalion of 487 men marched across it, and about 200 died. In 1852 the deck of the bridge at La Roche-Bernard, in Brittany, fell when the cables on one side broke.1 source1 source

The government ordered tests. On 18 and 19 March 1853 the director of public works for the district of Porto loaded the bridge and measured how far the cables sagged. The despatch on the results was signed by António Maria de Fontes Pereira de Melo.1 source1 source

The despatch said all doubts should now disappear, but it also ordered the director to examine the bridge thoroughly every year. When the concession ended, the bridge was tested again and passed. The worry that remained was rust. Part of the anchor cables lay in sealed chambers that could not be inspected, and nobody could see whether the iron wires there were still sound.1 source1 source

The Minister of Public Works, António de Serpa Pimentel, put that argument in the preamble to a bill for a competition for “a metal bridge over the river Douro” in front of Porto, “to replace the present suspension bridge”. Upstream, meanwhile, a single iron arch already crossed the gorge: the Maria Pia railway bridge, built by Gustave Eiffel's company, had opened in November 1877.2 sources2 sources

The competition for the new road bridge drew 12 proposals from 10 firms. The Belgian Société de Willebroeck won with a design by the engineer Théophile Seyrig: a single iron arch with two decks, one at the level of the quays and one at the level of the upper town. Work began in 1881, right beside the suspension bridge, and the upper deck of the Ponte Luís I opened on 31 October 1886.2 sources2 sources

The suspension bridge was dismantled in 1887. To take the cables off, the capitals on top of the obelisks had to come off as well. On the Gaia bank the obelisks themselves were then demolished. On the Porto bank they were left standing, because pulling them down would have destroyed the bridge house between them, and only the capitals were removed. They were restored much later.3 sources3 sources

It had carried traffic for 44 years. Azeredo calls it Porto's first permanent bridge and the shortest-lived of them all, and writes that within very few years the rapid rusting of its iron parts had raised doubts about its safety.2 sources2 sources

The Ponte Pênsil was the first fixed bridge anywhere on the Portuguese Douro. It put Porto's road crossing between two rocky knolls just upstream of the Ribeira, and the Luís I bridge that replaced it was built right beside it.2 sources2 sources

Its doubts also shaped what came next. Fear of corroded wire in places no inspector could reach is one reason the state asked for a metal bridge, and Seyrig's double-decker arch is now part of Porto's UNESCO World Heritage site.2 sources2 sources

The suspension bridge also left a detailed written record. Bigot's 1843 memoir describes how the wire was coated, spliced and tested, and how the cables were anchored. In the 1990s the Porto engineering professor Manuel de Azeredo drew on it to explain how the bridge was made.2 sources2 sources