Time Team attempt to find what is reputed to be the first railway viaduct. Built in 1790, to move coal efficiently from the mine to the Blaenavon Ironworks, one mountain over, horses drew wagons along its tracks for only about 10 years. Spoil from local mines has not only covered the viaduct, but filled the valleys so completely that it is difficult to find any clues as to where to dig. Thousands of tons of earth are moved to find the top of the viaduct, 12 meters below the modern surface. It is too dangerous to enter, but a camera is lowered for a peek. Elsewhere on the site, the remains of a manager's house and workers' cottages are found. As experimental archaeology, a small blast furnace is set up within the disused ironworks, and a Time Team logo (wooden pattern carved by Victor Ambrus) and cart wheels are cast.

• Tim Taylor

• Tony Robinson
• Bill Oddie
• Phil Harding