PONT-Y-CAFNAU BRIDGE 1793 Watkins George Merthyr Tydfil, Powys SO 038 072 {N51 45’ 17.7” W3 23’ 43.8”} This seemingly modest and simple iron bridge was a pioneering prototype in its day. Its name means “bridge of troughs” and it served a dual purpose – to provide a tramway across the River Taff for transporting limestone from the nearby Gurnos Quarry to the blast furnaces at the Cyfarthfa Iron Works while acting as an aqueduct to carry water to the famous “Aeolus” 50 foot diameter water wheel which powered the bellows. Watkins George, chief engineer at the works, designed and built this ingenious bridge consisting of a closed rectangular iron box two feet deep and a little over six feet wide to serve as the aqueduct for the water. On top of the box he ran the tram line tracks. The whole was supported by a double A frame of cast iron on either side whose ends terminate in the masonry abutments lining the river bank. Watkins George had trained as a carpenter, so it is not surprising that the cast iron pieces are joined by mortise and tenon joints, a woodworking technique which was copied in other early iron bridges such as the one at Coalbrookdale for ease of assembly. The total span is 47 feet.
The practical originality of George’s design was immediately appreciated by other pioneering bridge engineers. The Shropshire iron master William Reynolds (1758-1803) (son-in-law to Abraham Darby III who had built the Iron Bridge at Coalbrookdale in 1779) sketched the Pont-y-Cafnau bridge in 1794 and he worked with Thomas Telford on the Longdon-on-Tern aqueduct (1795) which carried the Shrewsbury canal over the River Tern in an iron “box” supported by diagonal cast iron beams.
Today, the setting for this landmark bridge is on the far side of an industrial estate on the site of the former Cyfarthfa Iron Works below Cyfarthfa Castle. It is so successfully obscured by an industrial tipster, debris, trash trees, and brambles that Christopher Parry on the staff at Cyfarthfa Castle had to personally lead me to the bridge because I could not find it.