Telford was involved in the construction of thousands of bridges. From the masonry bridges along the highland roads, to the elegant and gentle arc of Bewdley Bridge
, Telford's designs have a beauty that expresses his understanding and knowledge of architecture.
His innovative nature pushed Telford to experiment with cast iron road bridges. Buildwas Bridge, completed in 1796, was probably the second major iron bridge in Britain. It was modelled on the principles of timber rather than masonry construction, make a lighter-weight bridge that put less stress on its foundations than other early bridges whose designers had used masonry principles.
And true to his pioneering spirit, in 1800, with a young associate James Douglass, he put together a proposal to construct a cast iron bridge to span the Thames in place of London Bridge. The proposal, though seriously considered for many years, never went ahead because of a general lack of proved technical knowledge of cast iron. This was much to Telford's disappointment.
In 1810, Telford's experience and experiments led him to design a prefabricated iron arch a losenge lattice spandrel arch, to be precise. It was designed to be an economical option for use in locations where it was impractical or too expensive to use masonry. At least nine standardised-span arches were made and installed (1812-30) by William Hazeldine. Some of them, like those at Galton Bridge
in Birmingham and Holt Fleet Bridge
, are still in use today.
The bridges that Telford is best known for, though, are his wrought iron suspension bridges Menai Suspension Bridge
and Conwy Suspension Bridge
which fall along the Telford-engineered Holyhead Road
. They were a massive achievements, changing once-dangerous ferry crossings into safe road journeys and proving that suspension bridges were the most economical way to cover the greatest spans.
The Menai Bridge crosses the Menai Strait, between the Isle of Anglesey and Bangor in Wales. At times it was a hazardous project. The scale of the structure is vast, with an unprecedented span of nearly 177m, and the area is exposed to high winds and strong tides. Experimentation and constant testing were used to check the strength of the 16 wrought iron chains understandably, Telford was cautious.
To install the chains, they were attached to a pulley system and hauled using a force of 150 labourers. A fife band played to keep the men moving as one. The dangerous tides meant they had limited time to place each chain, so efficiency was everything.
It was a huge undertaking, one that was achieved through Telford's natural thoroughness in planning and relentless experimentation. He chose to work again with old colleagues John Wilson, who oversaw the masonry, and ironmaster William Hazeldine. Another key man was resident engineer William Provis, who wrote a full account of every stage of the work.
The last chain was put into position in 1825, and the ropes and tackle were taken down and moved east to the site of Conwy Bridge. Conwy is a smaller structure in a more-sheltered location crossing the estuary of the River Conwy so installing the chains was much easier. Both bridges were completed in 1826 and a surge of interest in building suspension bridges followed.
Towards the end of his life, in 1830, Telford entered a design competition for a crossing of the River Avon at the Clifton Gorge in Bristol. His proposal used two neo-Gothic towers rising dramatically from the gorge floor. His design failed to attract funding and the gorge was eventually spanned with the present suspension bridge, designed by the then up-coming engineer, Isambard Kingdom Brunel