It was not your usual embassy party. True, it opened with a banquet, but when it ended, the hosts burned the palace down. Then everyone moved next door, where brew mistresses poured nightcaps. And when that was over, the hosts set fire to the brewery, hurled tankards into the flames and said goodnight. And goodbye.

This was the end of the Peruvian desert settlement known as Cerro Baul, a team of archaeologists reported yesterday. Built atop a mesa in about A.D. 600 and continuously occupied for 400 years, Cerro Baul was perhaps the first diplomatic mission in the Americas.

And then suddenly -- but quite carefully -- it was torched and abandoned after a spectacular feast and beer party. The elite female brewers left their shawl pins in the brewery's ashes and may have joined in a final toast.

"They didn't torch every single building, but they got the best ones," said team member Patrick Ryan Williams of Chicago's Field Museum of Natural History. "They intended to leave and never come back, and apparently they didn't want anyone else to replace them."

And nobody did. The abandonment of Cerro Baul is a small piece of a much larger mystery surrounding the competing Wari and Tiwanaku cultures that vanished about 1,000 years ago, leaving a two-century power vacuum filled only with the emergence of the Inca empire in about 1300.

"The development of these states took hundreds of years, but the collapse appears to have been very sudden," said Andean archaeologist Brian Bauer of the University of Illinois at Chicago. "Some people link it to climate. Some link it to local revolts."

Cerro Baul, 8,500 feet above sea level, juts 2,000 feet above the Moquegua Valley near the three-country junction of Peru, Bolivia and Chile, on the northern edge of the Atacama Desert. It is the southernmost major Wari town, a citadel overlooking valley settlements linked to the Tiwanaku.

Although there is no evidence of war between the Wari and the Tiwanaku, there also is no indication of alliances. "I don't think it was a warm and fuzzy relationship," said University of California at San Diego archaeologist Paul Goldstein, who is excavating at Omo, a Tiwanaku site 12 miles from Cerro Baul. "It was probably an uneasy coexistence."

Reporting in the Proceedings of the National Academy of Sciences yesterday, the research team described how Cerro Baul developed as a largely ceremonial, and probably diplomatic, Wari outpost, in which drinking chicha, Andean beer made from corn or the red berries of pepper trees, played an important role.

"There isn't a lot of reason to be living up there, so they converted it into a place where visitors could feel awe and loyalty to the lords who lived there," Williams said. "Without a special kind of brew, it wouldn't have been a sacred place."

The 475-liter brewery was the largest in Peru at the time. Milled corn or pepper berry pulp was boiled in eight large pots, then fermented for a week. The process is largely the same today, except today's brewers ferment with yeast, whereas the Wari chewed the boiled pulp, using saliva enzymes to start the fermentation.

The researchers surmised that the brewers were noblewomen because of the shawl pins found in the brewery's boiling room. Williams said heat from the caldrons may have prompted the women to remove their llama and alpaca wool shawls, losing the pins in the ash that covered the floor.

The team suggested that Cerro Baul's "termination rites" began with a lavish dinner of vizcacha (Andean hare), venison, llama, alpaca and fish from the Pacific coast, washed down with chicha. Then the hosts torched the thatched roof and took everyone to the brewery.

There the revelers drank some more and set the brewery afire.

Only then did the noblemen throw away their ceremonial beakers. "The brewery was apparently abandoned last," the team wrote, "because chicha was essential to previous ceremonies."