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A very impressive example of an early cast iron arch bridge. Built 1812-15. Designed by Thomas Telford. It is a Category A listed structure.
The bridge has a single span of approximately 46 metres (151 ft) and was revolutionary for its time, in that it used an extremely slender arch which was not possible using traditional masonry construction. The ironwork was cast at the Plas Kynaston iron foundry at Cefn Mawr, near Ruabon in Denbighshire by William Hazledine, who cast a number of Telford bridges. The ironwork was transported from the foundry through the Ellesmere Canal and Pontcysyllte Aqueduct then by sea to Speymouth, where it was loaded onto wagons and taken to the site. Erected by William Stuttle, Telford's foreman. The stonework was by John Simpson of Shrewsbury.. At each end of the structure there are two 15 m (49 ft) high masonry mock-medieval towers, featuring arrow slits and miniature crenellated battlements.
A number of fine sketches by Geoffrey D. Hay show the details of construction of the ironwork . Mr Hay notes that a sister bridge was built two years earlier across the Dornoch Firth at Bonar, Sutherland.
Telford's later Mythe Bridge (Tewkesbury), Holt Fleet Bridge (Worcestershire), and Galton Bridge (Smethwick) are of very similar design, although the latter's castings came from the Horseley Ironworks rather than William Hazledine.
Testing in the 1960s revealed that the cast-iron had an unusually high tensile strength. This was probably specified by Telford because, unlike in traditional masonry arch bridges, some sections of the arch are not in compression under loading.
The bridge was in regular use until 1963, when it was closed for a major refurbishment. The side railings and spandrel members were replaced with new ironwork fabricated to match the originals. A restriction of 14 tons was placed on the bridge at this point. This, along with the fact that the road to the north of the bridge takes a sharp right-angled turn to avoid a rock face, made it unsuitable for modern vehicles. Despite this it carried foot and vehicle traffic across the River Spey until 1972, when its function was replaced by a reinforced concrete bridge built by Sir William Arrol & Co. which opened in 1970 and carries the A941 road today. Telford's bridge remains in good condition, and is still open to pedestrians and cyclists