Barmouth Viaduct is a Grade II* listed single-track wooden railway viaduct across the estuary of the River Mawddach near Barmouth, Wales. It is 900 yards (820 m) long and carries the Cambrian Line. It is the longest timber viaduct in Wales and one of the oldest in regular use in Britain. The bridge was designed by and constructed for the Aberystwith and Welsh Coast Railway on its line between Aberystwyth and Pwllheli. Work was authorised in 1861 and commenced in 1864. On 10 October 1867, the completed bridge was officially opened. [Wikipedia].