Because of the scale of the discovery, the archaeology team enlisted the help of the Forensic Anthropological Foundation of Guatemala.
The scientists found bones of 31 bodies in the grave. Forensic analysis determined that victims had been killed with spears and axes. Many of the bodies had been dismembered. The bones were dated to A.D. 800.
"The deposit was sealed in wet mud, and the preservation is extraordinary," Demarest said. "These are the best-looking bones I have ever seen. We could tell that these were not war wounds but that the people had been executed."
Precious jewelry found in the graveincluding jades, jaguar fang necklaces, and coast shellsindicates that the victims were nobles, possibly from the royal palace.
In a shallow grave 80 yards (73 meters) away, the researchers made another spectacular discovery: two people who appear to be the king and queen of Cancuén buried in full regalia.
Demarest says a necklace found on the king has an inscription that says in part, "Kan Maax. Holy Lord of Cancuén."
In the years preceding the massacre, warfare had spread across the western region of the ancient Maya world. The unrest seems to have reached Cancuén in A.D. 800.
Unfinished construction around the city, including a system of hastily built stone and wooden palisade walls, suggests that the residents may have known that they were going to come under attack.
"The defense obviously failed," Demarest said.
While commoners may have run away or been taken captive, noblesmen, women, and childrenwere lined up and executed. The bodies were then deposited with some ceremony in the sacred cistern at the palace entrance, the researchers speculate.
There is no evidence that the city was conquered. Instead the assailants seem to have abandoned it after their attack.
"The massacre is an exceptionally dramatic example of the violence marking the end of royal court life and divine kingship in classic Maya civilzation," said David Freidel, a Maya expert at Southern Methodist University in Dallas, Texas.
At least one Maya expert declined to comment on the discovery, citing that the findings had not yet been published in an academic journal and had not been peer reviewed.
Experts have fiercely debated the cause of the quick demise of Maya society, which once ranged from Mexico's Yucatán peninsula to Honduras.
Some of the theories about the collapse include such factors as overpopulation, drought, political conflict, and loss of the royal court.
While the massacre discovery seems to suggest that warfare played an important role, Demarest believes there is no one "silver bullet" to explain the decline of the Maya culture.
"What we are seeing [with massacres like these] is the beginning of the end," he said. "That doesn't mean they caused the collapse. We're moving away from this idea that it had to be this one dramatic reason for the collapse."
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