While laying Brunel's Great Western Railway line 50 miles from London, navvies discovered mosaic floors indicating a Roman villa. The mosaics were broken up and the whole site ignored, until recent photographs of cropmarks showed the outline of the villa, among other features. Geophysics signals are also very strong. The trouble is, the diggers can find no structure beneath the surface. They are joined by Bernard Thomason from English Heritage, mosaics expert David Neal, Tim Allen of Oxford Archaeological Unit, and Jillian Greenaway from Reading Museum. Reconstructor Chris Owen supervises the recreation of a mosaic using thousands of tesserae.

• Tim Taylor

• Suzannah Lipscomb
• Tony Robinson
• Phil Harding