Drogheda Viaduct one of the best examples of Ireland’s engineering and architectural heritage.Vimeo

There is an old rumor in Drogheda, Co Louth that the railway viaduct over the river Boyne was built on foundations of cotton wool. It’s not very comforting for train passengers on the busy Dublin-Belfast line, but like all good rumors there is some truth to the story. The Boyne Viaduct was built nearly 160 years ago and a recent RTÉ documentary investigated the construction of what is regarded as the finest railway bridge ever constructed in Ireland.

“It is one of Ireland's best examples of ambitious Victorian industrial engineering. And one of the great adventures of building Ireland,” says engineer Tim Joyce, presenter of the documentary. The program on Drogheda’s viaduct is one of a series called “Building Ireland”, exploring the best examples of Ireland’s engineering and architectural heritage.

BUILDING IRELAND - The Boyne Viaduct at Drogheda from Esras Films on Vimeo.

At the onset of the railway age, it was inevitable that a railway link was needed between the two largest cities on the island – the administrative capital Dublin and the industrial center Belfast. At Drogheda, a way had to be found to bridge the 1750 foot span of the Boyne Valley. Stone arches were planned for the main parts of the bridge, but the span across the river would have to be made of iron. Nothing like it anywhere had ever been attempted and construction was full of problems and controversies. On completion it was considered the engineering marvel of the age.

“Sir John McNeill, who was the great engineer of the day and a native of Dundalk, was the main bridge designer,” explains local historian Brendan Matthews. McNeill had studied similar type bridges made of timber, especially in America, so it was a big decision to build in iron.

Engineering contractor William Evans from Bristol undertook the construction of the bridge itself and he began by building stone arches on the north side of the river; fifteen stone arches were proposed to support the elevated rail line needed to bridge the valley. Working inwards from the riverbank towards the embankments, the scaffolding dominated the skyline overshadowing the town. The last stages of the stone construction were the two free standing stone piers in the riverbed.

A year into the build, construction was running behind schedule, facing technical problems and industrial disputes. It was all bad news for the building contractor William Evans as Matthews explains, “Evans began this work in 1852 and by early 1853 he had already got the arches done on the north side and at the same time he had his men working in the river constructing the two piers, numbered 13 and 14.”

These free-standing piers had to be built on solid bedrock. Workers built a cofferdam, pumped out the water and began digging through the mud and silt of the riverbed – 20, 30, 40 feet down and still no luck. To add to the problems, a storm on Christmas Day 1852 brought two cranes crashing down into the Boyne. William Evans couldn’t sustain the financial pressure and he was declared bankrupt. Despite the series of disasters, Evans committed to stay with the project until foundations for the pier were reached.

The free standing Pier number 14 caused the greatest problem. As the workers kept digging down, water was continually seeping into the cofferdam. In order to stop this, they needed something to plug the holes. The answer? Sheep’s wool. They bought up as much as they could get their hands on from all over the north east of the country. “This is where the myth comes from in Drogheda, even to the present day, that the piers of the viaduct are built on cotton wool”, says Brendan Matthews.

Endless bales of wool were stuffed in to keep the cofferdam watertight. And when the diggers eventually reached the bedrock, the cofferdam was left in position and mortar was poured in around the stone foundations. So it is truthful to say that wool helped build the foundations of the Boyne Viaduct!

With the stonework complete, the innovative wrought iron lattice superstructure was put in place. As TV Presenter Tim Joyce explains, “finally, after all the set-backs, on the April 5, 1855, without ceremony, the first train crossed the viaduct.” The creation of a seamless rail link between Dublin and Belfast was an engineering breakthrough with economic, social, and political benefits for the island. This viaduct was a breakthrough into the modern age of technology and fast communication.

The RTÉ TV series "Building Ireland" was produced by Esras Films in Dublin and looks at the great stories of engineering and architecture. For more or to purchase your DVD box set contact [email protected]