A three-day dig revealed an elaborate mosaic floor
The discovery was made after pieces of floor tile were disturbed by a plough in a field at Dinnington, near Ilminster.
A three-day archaeological dig, filmed for a television documentary, has revealed a large mosaic floor with an elaborate diamond and rope patterned border.
Somerset County Council archaeologist Bob Croft said it was a building complex more than 100m long and believed to be the home of a wealthy Briton.
Landowner's daughter, Trudy Ridgers, said she saw the mosaic tiles by chance, while out walking her dog.
"If I had been a few inches either side, I wouldn't have hit that particular place," she told the BBC.
The villa is a short distance from Lopen, where the most spectacular Roman floor to be discovered in Britain for 50 years was found last year.
Both sites are close to a Roman road, the Fosse Way, which is now the A303.
It stretched from Lincoln to Exeter and was one of the major routes of Roman Britain.
This latest discovery has prompted the suggestion that the the Fosse Way was a 4th Century millionaires' row.
Mr Croft said: "It was clearly a very popular area to be in the Roman period.
"All along the Fosse Way, about every couple of miles, it appears there are very large Roman buildings."
The villa will be covered over with earth again on Saturday to protect it until enough money can be raised to dig for longer.