Menai Suspension Bridge

Early Suspension Bridge Showed That Great Spans Were Possible

Lithograph of the Menai Suspension Bridge
The Menai Suspension Bridge. Getty Images

When engineer Thomas Telford proposed building a great suspension bridge over a tricky body of water in Wales in the early 1800s the project was thought impossible.

The basic principle of a suspension bridge, the hanging of a roadway from supports at either end, dates back to ancient times. Yet early suspension bridges tended to be used to span narrow ravines or small bodies of water. 

In the early 19th century, an American engineer, James Finley, patented the design of a suspension bridge which used metal cables or chains to suspend the roadways.

Finley's design made it practical to build spans of up to 250 feet.

That was less than half the distance Telford wanted to span across the Menai Straits in Wales. Battling difficult conditions, and considerable skepticism, Telford succeeded in building a spectacular bridge that would inspire engineers for decades.

An Impossible Span

The Isle of Anglesey, off the northwest coast of Wales, is separated from the mainland by the narrow but treacherous Menai Strait. The strait had been crossed by ferries since ancient times, but the difficult currents could make the trip perilous.

In one particular tragedy, in 1785, a ferry capsized, stranding 55 passengers on a sandbar in the strait. Rescue parties set out in small boats, but the currents and approaching dark made it nearly impossible to reach the ferry’s passengers. Only one person survived.

Thomas Telford Took On the Challenge

The Scottish engineer Thomas Telford had been making a great name for himself as a brilliant engineer.

Telford had built roads, bridges, canals, and aqueducts across Great Britain, and had pioneered the use of iron in bridge construction.

In 1818 Telford proposed his visionary plan to bridge the Menai Strait. He intended to construct a bridge in which the roadway would be suspended from masonry towers by enormous iron chains.

Years of Construction

Construction of the stone towers began in 1820, and proceeded for more than four years. In the spring of 1825 all that remained was the construction of the main span, which would be nearly 600 feet long and approximately 100 feet above the strait.

The first colossal iron chain was hung from the Wales tower of the bridge, and on April 26, 1825, as thousands of amazed spectators watched, one end of the chain was played out across the strait by a raft. As scores of workmen strained, the chain was hoisted up to the Anglesey tower. In less than two hours, the chain was across the strait and bolted into place.

The Menai Strait Was Bridged

Work on 15 other sets of chains, which resembled enormous bicycle chains, continued until July 1825. Throughout the end of the year construction of the center span and roadway proceeded.

When finished, the Menai Suspension Bridge, with its 580 foot center span, was the longest span in the world. Sailing ships with tall masts could sail under it, a remarkable feature for its day.

The bridge was a highpoint of Thomas Telford's career, and proved the effectiveness of suspension bridges.

A Very Practical Bridge

On January 30, 1826 the Menai Straits bridge opened, and a mail coach carrying letters from London to Holyhead, a city on the isle of Anglesey, passed across.

Telford’s design for the bridge is considered brilliant, yet he did not fully anticipate the effect of the wind. A severe gale in 1839 wrecked the roadway and after repairs some bracing was added to steady the suspension chains.

The bridge was repaired and rebuilt again in 1892. Between 1938 and 1942 the bridge underwent substantial renovations, and the original iron suspension chains were replaced by chains of steel.

An Enduring Marvel

The Menai Suspension Bridge is still in service, more than 180 years after its opening. And despite the improvements over the years, it retains the graceful form of Telford's original design.

The success of the bridge established that suspension bridges would be the dominant form of bridges for long spans, and thus contributed enormously to future bridge design.

Later bridges, such as two designed by John Roebling, the Niagara Suspension Bridge and the Brooklyn Bridge, were partly inspired by Telford's masterpiece.