Heritage Locations

Iron Bridge


World's first cast iron arch bridge

Constructor:
Unclassified

Period of construction:
1750 - 1799

Transport Trust plaque:
No

Transport Mode:
Road

Address:
Ironbridge, Telford, TF8 7AL 

Postcode:
TF8 7AL

Nearest Town:
Ironbridge

Heritage Centre:
Yes


The area around Ironbridge is described as the ‘Birthplace of the Industrial Revolution' because it is near the place where Abraham Darby I perfected the technique of smelting iron with coke, allowing much cheaper production of iron. The grandson of the first Abraham Darby, Abraham Darby III, built the famous bridge - originally designed by Thomas Farnolls Pritchard - to link the two areas. Construction began in 1779 and the bridge opened on New Year's Day 1781. Soon afterwards the ancient Madeley market was relocated to the new purpose built square and Georgian Butter Cross and the former dispersed settlement of Madeley Wood gained a planned urban focus as Ironbridge, the commercial and administrative centre of the Coalbrookdale coalfield. The Iron Bridge proprietors also built the Tontine Hotel to accommodate visitors to the new Bridge and the industrial sights of the Severn Gorge.

By the 19th century, Ironbridge had had many well-known visitors including Benjamin Disraeli, but by the mid-20th century the village was in decline. In 1986 though, Ironbridge became part of a UNESCO World Heritage Site, which covers the wider Ironbridge Gorge area, and has become a major tourist attraction within Shropshire.

In the early eighteenth century the only way to cross the Severn Gorge was by ferry. However, the industries that were growing in the area of Coalbrookdale and Broseley needed a more reliable crossing. In 1773, Thomas Farnolls Pritchard wrote to a local ironmaster, John Wilkinson of Broseley, to suggest building a bridge out of cast iron. By 1775, Pritchard had finalised the plans, and Abraham Darby III, an ironmaster working at Coalbrookdale in the gorge, was commissioned to cast and build the bridge.

Shares were issued to raise the £3,200 required, and Darby agreed to fund any overspend. Although it had been predicted that 300 tons of iron would be needed (costing £7 a ton), in the end 379 tons were used, costing Darby and his company nearly £3,000. There would be many other costs to bear (masonry abutments, assembly etc), so that the project was far more expensive than first envisaged. Darby bore most of the cost over-run, and was in debt for the rest of his short life.

Being the first of its kind, the construction had no precedent; the method chosen to create the structure was therefore based on carpentry. Each member of the frame was cast separately, and fastenings followed those used in woodworking, such as the mortise and tenon and blind dovetail joints. Bolts were used to fasten the half-ribs together at the crown of the arch. Very large parts were needed to create a structure to span 30 m. (100 ft.) rising to 18 m. (60 ft.) above the river. The largest parts were the half-ribs, each about 21 m. (70 ft.) long and weighing 5.25 tons. The bridge comprises more than 800 castings of 12 basic types.

The bridge was raised in the summer of 1779, and it was opened on New Year's Day 1781. In 2001, the BBC screened a documentary in which a half-sized model of the bridge was built to test recent research over the construction. Instead of large timber towers, a pair of uprights with a crosspiece was used to erect each of the ribs in sequence. The abutments were built afterwards.

Just a few years after the construction of the bridge, cracks were appearing in the masonry abutments, caused by ground movement. Some of the present-day cracks in the cast iron may date from this time, although others are probably casting cracks. Some were pinned with wrought iron straps, but others have been left free. By 1802, the southern stone abutment had to be demolished, and replaced with temporary wooden arches, before eventually being replaced by iron arches. Many of the cracks visible today in the bridge have been left untouched.

The bridge was over-designed, and subsequent bridges such as those built by Thomas Telford used much less cast iron. For example, his cast iron arch bridge at Buildwas, upstream from Ironbridge, used less than half the weight for a greater span of 40 m. (130 ft.). However, it suffered similar problems of abutment movement and was replaced in 1902. The cast iron bridge at Coalport downstream, built in 1818, is even more impressive because of its lean, streamlined design, and it still carries vehicular traffic. It has about half the weight of cast iron and is longer than the earlier Iron bridge structure. It was renovated in 2004.

In 1972 a programme of major repairs took place on the foundations of the bridge. It involved creating a ferro-concrete counter-arch under the river. In 1999-2000, the bridge was renovated again, with replacement of the cast iron road plates with steel plates, and a lightweight top surface. Further information on the manufacture of the cast iron parts has emerged. While the smaller parts were cast using wooden patterns, the large ribs were cast freely into excavated moulds in the casting sand.

It is a scheduled Ancient Monument and is listed Grade I. Ironbridge Gorge is a World Heritage Site.


Bibliography:

Allen, Robert C., The British Industrial Revolution in Global Perspective, Cambridge University Press, ISBN-10: 0521868270 (2009)

Cossons, Neil & Trinder, Barrie, The Iron Bridge: Symbol of the Industrial Revolution, Phillimore & Co Ltd, ISBN-10: 1860772307  (2002)

Cragg, Roger (Editor) Civil Engineering Heritage: Wales and West England, Thomas Telford Ltd (1997)

Labouchere, Rachel, Abiah Darby of Coalbrookdale, 1716-1793: Wife of Abraham Darby II, William Sessions, ISBN-10: 1850720177 (1988)

Muter, W. Grant, The Buildings of an Industrial Community: Coalbrookdale and Ironbridge, Phillimore & Co Ltd, ISBN-10: 0850333423 (1979)

Raistrick, Arthur, Dynasty of Ironfounders: Darbys and Coalbrookdale, David & Charles, ISBN-10: 0715358367 (1973)

Read, Brian, Men of Iron - A Tale of Coalbrookdale and the making in Shropshire of the first Iron Bridge in 1779, Littlehampton Books, ISBN-10: 0437701123 (1974)

Trinder, Barrie, The Industrial Revolution in Shropshire, Phillimore & Co Ltd, ISBN-10: 1860771335 (2000)

Trinder, Barrie, The Most Extraordinary District in the World: Ironbridge and Coalbrookdale, Phillimore & Co Ltd, ISBN-10: 1860773753 (2005)

Weightman, Gavin, The Industrial Revolutionaries: The Creation of the Modern World 1776-1914, Atlantic Books, ISBN-10: 1843545853 (2008)



Opening Times:
Viewable at all times.

How To Find:
By road: Off A5223/A4169 in the centre of Ironbridge

Facilities:


Weather Feed currently unavailable.