What is "pont-y-cafnau"

The Pont-y-Cafnau , sometimes written Pont y Cafnau or Pontycafnau, is a long iron truss bridge over the River Taff in Merthyr Tydfil, Wales. The bridge was designed by Watkin George and built in 1793 for his employer, the Cyfarthfa Ironworks, to support both a tramway and an aqueduct to carry limestone and water into the works. A Grade II* listed building and Scheduled Ancient Monument, the Pont-y-Cafnau is the world's earliest surviving iron railway bridge.