BOXFORD, England – Their ages range from 9 to about 80. They include a butcher and a builder. Some devoted vacation days to laboring on their hands and knees in an open field.

The group of amateur archaeologists — 55 in all, though only two dozen toiled on a typical day — were part of an excavation project near the village of Boxford, in southern England. They had to contend not just with days of backbreaking work, but also with a daunting, two-week deadline to complete the challenging dig.

Their commitment was handsomely repaid, though, in a few magical moments one Saturday in August. As a layer of soil was carefully scooped away, small, muddy pieces of red-colored tiling glinted in the sunlight, probably for the first time in more than 1½ millenniums.

The mosaic that slowly emerged from the earth is part of a Roman villa, thought to date from 380 A.D., toward the end of the period of Roman domination of England. The find is being described as the most important of its type in Britain in more than half a century, and in this picturesque, riverside village of thatched cottages, the scale of the discovery is still sinking in.

While surveys had shown something of interest beneath this stretch of gently undulating English countryside, they had suggested that it was a medium-size Roman villa that was unlikely to yield anything exceptional.

Among the first to spot it was Joy Appleton, who leads the Boxford History Project and who was a driving force behind the excavation.

"I was stunned into silence," Appleton recalled of her first sight of the small red tiles, each the size of her fingernail. "Which is unusual."

"I will never forget that moment," said Matt Nichol, a professional archaeologist who was supervising the dig. "It was down to the volunteers, it really was. I get quite emotional about it; it was something to see their drive."

Experts say they believe that the mosaic depicts Bellerophon, a hero of Greek mythology who was sent to kill the chimera, a fire-breathing monster with the head of a lion, the torso of a goat and the tail of a serpent. Hercules is also thought to be featured, fighting a centaur, and so is Cupid.

According to Anthony Beeson, a specialist in classical art and a member of the board of the Association for Roman Archaeology, the discovery is important for several reasons.

"It is so unusual because it has all sorts of quirks which you don't expect, and it has subjects on it that are completely alien to mosaics in this country," he said.

For Appleton, the discovery has filled in part of a missing link in the history of Boxford, a village of about 300 inhabitants. Evidence of Stone, Bronze and Iron Age life had been discovered, and there is a Saxon window in the local church that dates to the period before the Norman invasion of 1066.

Given the geographical location, and the quality of the agricultural land, Appleton was confident that this was also the site of a Roman settlement, a conviction reinforced by the discovery of several artifacts from that period.

Appleton and Nichol hope to uncover the rest of the site next year, though that will depend on whether funding can be raised.