"We have long wondered what else the prehistoric Mayan people were growing and eating besides corn and beans, so finding this field was a jackpot of sorts for us," anthropologist Payson Sheets, who led the expedition, said in a statement.

"Manioc's extraordinary productivity may help explain how the Classic Maya at huge sites like Tikal in Guatemala and Copan in Honduras supported such dense populations."

The manioc field lay under 10 feet (3 metres) of ash at the ancient village of Ceren, 15 miles (24 km) west of San Salvador, Sheets said.

Like Italy's Pompeii, Ceren's buildings, artifacts and landscape were preserved by the sudden eruption of a volcano -- in this case the nearby Loma Caldera volcano about 600 A.D.

"What we essentially found was a freshly planted manioc field that was 1,400 years old," Sheets said.

The team, which uses ground-penetrating radar to help direct excavations, has found 12 buildings at Ceren, including homes, storehouses, workshops, kitchens, religious buildings and a community sauna.

Several dozen other structures located with ground-penetrating radar remain buried under up to 17 feet (5 metres) of ash, said Sheets.