page_title: The Iron Bridge
section_title: Construction
hierarchical_section_title: The Iron Bridge / Construction
caption_attribution_description: English: The roadway of the Iron Bridge looking north in February 2019. Seen here is the dark red paint added in the 2018 restoration.
context_page_description: The Iron Bridge is a cast iron arch bridge that crosses the River Severn in Shropshire, England. Opened in 1781, it was the first major bridge in the world to be made of cast iron. Its success inspired the widespread use of cast iron as a structural material, and today the bridge is celebrated as a symbol of the Industrial Revolution.
  The geography of the deep Ironbridge Gorge, formed by glacial action during the last ice age, meant that there are industrially useful deposits of coal, iron ore, limestone and fire clay present near the surface where they are readily mined, but also that it was difficult to build a bridge across the river at this location. To cope with the instability of the banks and the need to maintain a navigable channel in the river, a single span iron bridge was proposed by Thomas Farnolls Pritchard. After initial uncertainty about the use of iron, construction took place over 2 years, with Abraham Darby III responsible for the ironworks. The bridge crosses the Ironbridge Gorge with a main span of 100 ft 6 in, allowing sufficient clearance for boats to pass underneath.
  In 1934 it was designated a scheduled monument and closed to vehicular traffic.
context_section_description: The site, adjacent to where a ferry had run between Madeley and Benthall, was chosen for its high approaches on each side and the relative solidity of the ground. The Act of Parliament described how the bridge was to be built from a point in Benthall parish near the house of Samuel Barnett to a point on the opposite shore near the house of Thomas Crumpton. Pritchard died on 21 December 1777 in his towerhouse at Eyton on Severn, only a month after work had begun, having been ill for over a year.
  The bridge is built from five sectional cast-iron ribs that give a span of 100 feet 6 inches (30.6 m). The construction of the bridge used 378 long tons 10 cwt (847,800 lb or 384.6 t) of iron, and there are almost 1,700 individual components, the heaviest weighing 5 long tons 5 cwt (11,800 lb or 5.3 t). Components were cast individually to fit with each other, rather than being of standard sizes, with discrepancies of up to several centimetres between 'identical' components in different locations.
  The masonry and abutments were constructed between 1777 and 1778, and the ribs were lifted into place in the summer of 1779. The bridge first spanned the river on 2 July 1779, and it was opened to traffic on 1 January 1781.
  In 1997, a watercolour by Elias Martin was discovered in a Stockholm museum, which showed the bridge under construction in 1779. The painting shows a moveable wooden scaffold consisting of derrick poles standing in the river bed being used as a crane to position the half-ribs of the bridge, which had been taken to the site by boat from Darby's foundry 500 metres (1,600 ft) downstream. Using the approach depicted in the painting, a half-size replica of the main section of the bridge was built in 2001 as part of the research for the BBC's Timewatch programme, which was shown the following year.
caption: Pedestrians crossing the Iron Bridge with Ironbridge in the background in 2019, after the bridge had been conserved and the metalwork painted red.
exif: {"Image ImageDescription": "", "Image Make": "SONY", "Image Model": "DSC-HX60", "Image Orientation": "Horizontal (normal)", "Image XResolution": "350", "Image YResolution": "350", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "DSC-HX60 v2.10", "Image DateTime": "2019:02:23 10:52:12", "Image YCbCrPositioning": "Co-sited", "Image ExifOffset": "286", "Image PrintIM": "[80, 114, 105, 110, 116, 73, 77, 0, 48, 51, 48, 48, 0, 0, 2, 0, 2, 0, 1, 0, 0, 0, 1, 1, 1, 0, 0, 0]", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail ImageDescription": "", "Thumbnail Make": "SONY", "Thumbnail Model": "DSC-HX60", "Thumbnail Orientation": "Horizontal (normal)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail Software": "DSC-HX60 v2.10", "Thumbnail DateTime": "2019:02:23 10:52:12", "Thumbnail JPEGInterchangeFormat": "31908", "Thumbnail JPEGInterchangeFormatLength": "7781", "Thumbnail YCbCrPositioning": "Co-sited", "EXIF ExposureTime": "1/1000", "EXIF FNumber": "7/2", "EXIF ExposureProgram": "Program Normal", "EXIF ISOSpeedRatings": "80", "EXIF SensitivityType": "Recommended Exposure Index", "EXIF RecommendedExposureIndex": "80", "EXIF ExifVersion": "0230", "EXIF DateTimeOriginal": "2019:02:23 10:52:12", "EXIF DateTimeDigitized": "2019:02:23 10:52:12", "EXIF ComponentsConfiguration": "YCbCr", "EXIF CompressedBitsPerPixel": "3", "EXIF BrightnessValue": "12467/1280", "EXIF ExposureBiasValue": "0", "EXIF MaxApertureValue": "463/128", "EXIF MeteringMode": "Pattern", "EXIF LightSource": "Unknown", "EXIF Flash": "Flash did not fire, auto mode", "EXIF FocalLength": "43/10", "EXIF FlashPixVersion": "0100", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "5184", "EXIF ExifImageLength": "3888", "Interoperability InteroperabilityIndex": "R98", "Interoperability InteroperabilityVersion": "[48, 49, 48, 48]", "EXIF InteroperabilityOffset": "31616", "EXIF FileSource": "Digital Camera", "EXIF SceneType": "Directly Photographed", "EXIF CustomRendered": "Normal", "EXIF ExposureMode": "Auto Exposure", "EXIF WhiteBalance": "Auto", "EXIF DigitalZoomRatio": "1", "EXIF SceneCaptureType": "Standard", "EXIF Contrast": "Normal", "EXIF Saturation": "Normal", "EXIF Sharpness": "Normal", "EXIF LensSpecification": "[43/10, 129, 7/2, 63/10]"}