Moseley believes the location may have been chosen to show off the Wari's prowess and to serve as an impressive embassy to the Tiwanaku, whose nearest city was just five miles (eight kilometers) away.
"We think this is where the two nations conducted business, though what they were doing and what sort of negotiations were going on is not terribly evident," he said.
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The two societies were not in direct economic competition with each other, which may explain why there is no evidence of fighting between them.
The Wari are believed to have been a more secular and militant nation than the religious and mercantile Tiwanaku. But the two peoples worshipped the same main deity, Wiracocha, the "staff god" who controlled life and death.
Another essential sacrament shared by both cultures was chicha, a fermented alcoholic brew similar to beer. Made from corn, the beverage was consumed in massive quantities during drinking rituals.
"You couldn't have a ceremony without ritual intoxication," Moseley said. "People would drink until they fell down, then get up and start drinking again."
It is unclear why the Wari and Tiwanaku empires began to decline around A.D. 1000, though some researchers speculate that a long-term drought in the region may be to blame.
"The Moquegua Valley and, more specifically, the site of Cerro Baúl is critical for us to understand the fall of one of the largest empires of the new world," said Brian Bauer, an anthropology professor at the University of Illinois at Chicago.
The demise of the Tiwanaku empire may have started first, which would have diminished the importance of the Cerro Baúl settlement to the Wari, encouraging the Wari to abandon the town.
"Evidence from a number of sites in the Andes suggests that the Wari state ended suddenly and that various of their administrative centers were quickly abandoned," Bauer said.
"The work of Moseley and his colleagues provides important new data to understand when and how the Wari ended their rule over much of what is now modern-day Peru."
By examining the monumental ruins, Moseley's team found evidence that buildings' roofs had been burned and ceramic drinking vessels had been ritually smashed.
"The feel we get is that the abandonment was probably a political decision made back at the imperial capital and that the locals executed it in a prescribed manner," Moseley said.
The evacuation of the enclave began with the brewing of a final batch of chicha, a process that took a week, Mosley said.
The discovery of several shawl clips in the brewery indicates that high-status women brewed the chicha, a practice used by the Inca centuries later.
The Cerro Baúl brewery had a capacity of 475 gallons (1,800 liters) per batch. Once fermented, the beer was spiced with pepper-tree seeds, creating a version of chicha reserved for nobles.
The pieces found in the ruins suggest that 28 local lords assembled in the brewery courtyard.
Lesser lords drank from vessels that held 12 ounces (355 milliliters), but four senior leaders are believed to have used mugs featuring elaborate iconography that held up to a half gallon (two liters) of chicha.
"People drank in sort of rank order," Moseley said. "No doubt there is a lot of ritual toasting going on."
Animal bones found at the site indicate that the drinking ritual was accompanied by a banquet at the palace that included deer, llama, and several types of fish.
The ceremonies ended with the participants igniting the combustible parts of the palace, temple, and brewery. The ceremonial vessels used in the drinking ritual were thrown into the flames.
"It may be that this use of fire to close particularly important buildings is a way of keeping other people from defiling them or reusing them," Moseley said.
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