Building the Iron Bridge

The full story of how the bridge was built will probably never be known - only one image of work in progress survives, a watercolour on display in a Stockholm museum. Some of our questions about the building of the bridge are answered here.

Shrewsbury architect Thomas Farnolls Pritchard first suggested to John Wilkinson in 1773 that an iron bridge be built over the Severn. Pritchard later designed the bridge but died in December 1777, only a month after work began.Thomas Farnolls Pritchard
Thomas Farnolls Pritchard
Acc No: 1978.218.1
anonymous (artist)

The third design is most like the bridge that was actually built, differing in allowing for a towpath alongside the river.
Design for an Iron Bridge
Design for an Iron Bridge
Acc No: 1986.8609

The earliest estimate of costs for building the Iron Bridge drawn up by Abraham Darby and Thomas Farnolls Pritchard was £3200. The Rev. Edward Harries contributed £525 in a share subscription of 1777 which raised £3,150.
Iron Bridge Share Cerificate
Iron Bridge Share Cerificate
Acc No: 1972.90

Molten iron runs from the furnace into a sand pig bed. It is uncertain whether the parts for the Iron Bridge were cast directly from the furnace, or a stock of pig iron was made like this to be remelted and cast into the correct shapes.
Inside of a smelting house near Broseley
Inside of a smelting house near Broseley
Acc No: AE185.762
Lowry, Wilson (engraver)
Robertson, George (artist)

Sunderland Bridge was a much larger undertaking than the Iron Bridge. Scaffold was used successfully to construct the bridge without obstructing the heavy traffic on the river, and may have been used in the construction of the Iron Bridge.
Sunderland Bridge
East view of the Cast Iron Bridge over the River Wear at Sunderland in the County of Durham
Acc No: AE185.411
Raffield, J. (aquatinter)
Clarke, Robert (artist)

Darby's workers adapted woodworking techniques to take into account the different properties of cast iron. Blind dovetailed joints, where only half the thickness of the iron is in the shape of a dovetail, join the arched ribs to the radials.
Blind dovetail joint on the Iron Bridge
Blind dovetail joint on the Iron Bridge
Acc No: F20.28