For the past three years, as part of a community project, archaeologists in England have been inviting volunteer history enthusiasts to help excavate three Roman sites near the village of Boxford, in West Berkshire. As Maev Kennedy reports for the Guardian, the program was just two weeks away from concluding when the amateur excavators made a stunning discovery: a large, colorful mosaic depicting the dramatic tale of a mythical hero.

The mosaic measures more than six meters in length, according to a statement from Cotswold Archaeology, which oversees the program in conjunction with the Boxford History Project and the Berkshire Archaeology Research Group. Only one side has been unearthed thus far, but the work is packed with detail and action. It tells the story of the Greek hero Bellerophon, known in myth for capturing the winged horse Pegasus and for slaying the Chimera, a fearsome, fire-breathing monster with the body and face of a lion, a goat’s head jutting from its back, and a tail ending in a serpent’s head.

On the portion of the mosaic uncovered during the excavation, Bellerophon can be seen riding Pegasus, appearing at the court of a king—either Iobates or Proteus, who both appear in the Bellerophon myth—and attacking the Chimera. Intriguingly, the monster is shown fighting back; according to the Cotswold Archaeology statement, most other depictions of the myth in Britain depict the Chimera fleeing. Experts believe that other scenes portray Hercules fighting a centaur, and Cupid holding a wreath.

The mosaic dates to approximately 380 A.D., reports Martin Evans of the Telegraph, and it is very well preserved. Anthony Beeson, a classical art expert and member of the Association for the Study and Preservation of Roman Mosaics, said that the work is “without question the most exciting mosaic discovery made in Britain in the last fifty years,” according to the statement.

Throughout the three-year excavation project, amateur archaeologists have helped uncover a number of other important finds, including a Roman villa, a bathhouse and a farm building. The mosaic was found in a room at the south end of the villa, which was not particularly large, but had been subjected to a number of improvements over the years. As Neil Holbrook of Cotswold Archaeology notes in the statement, the mosaic deepens our understanding of the lifestyle and aspirations of the villa’s former owner.

“That person wanted to project an image of themselves as a cultivated person of taste—someone familiar with classical mythology and high Roman culture, despite the fact that their villa was of relatively modest size in a remote part of the Roman empire,” he says. “While this person was most probably of British origin, they wanted to be regarded by their friends, neighbors and subservients as a proper Roman.”

Now that the community project has come to an end, the site has been backfilled. But experts say they hope to return to the area and uncover the rest of the mosaic—along with other ancient treasures that the site may hold.