The demise of Mexico's enigmatic pre-Hispanic city of Teotihuacan stemmed from a conflict among the civilization's elite classes, with buildings set ablaze in the clash, according to a study.
The famed pyramids of the Sun and Moon are among the majestic structures that remain at the tourist site near Mexico City, centuries after Teotihuacan's population vanished.
What caused the civilization to abandon the sprawling city in the 7th century has been the subject of many studies, with political, economic and social problems believed to be behind the exodus.
Linda Manzanilla, an anthropologist at the National Autonomous University of Mexico, now says the collapse was the result of a confrontation between the city's rulers and an "intermediate elite" comprised of entrepreneurs.
The governing class ruled like a "corporate organization" that distributed power among each other, without dynasties or kings -- unlike the Mayan civilization elsewhere in Mexico.
The city, which at some point housed 125,000 people, was divided into neighborhoods where "mid-rank nobles who acted like entrepreneurs" competed to show off the best luxury goods, she told AFP.
"They competed among themselves to bring raw materials, and luxury goods from distant regions, and demonstrate the most attractive and rarest items," said Manzanilla.
This rivalry gave rise to tensions within the city, said Manzanilla, whose conclusions were published in the Proceedings of the National Academy of Sciences in the United States.
The clash, she said, finally took place when "the governing elite realized that the neighborhood elites around the center of the city were getting richer and functioning in an autonomous way."
"They tried to take control, but it was too late," the researcher said.
Around 550 A.D., the revolt of the neighborhood entrepreneur led to the destruction of the Street of the Dead, which is now a major tourist site, and the main buildings of the ruling elite.
Her study found no traces of a foreign invasion.
- Hard workers joined revolt -
"Little by little, the site was emptied until inhabitants of (central and north Mexico) arrived in the city to loot it, said Manzanilla, who has been excavating the site for 40 years.
Another reason for the collapse was the deteriorating situation of residents of the city's periphery who were used as cheap labor.
The city's outskirts were inhabited by peoples who had fled volcanic eruptions in other parts of Mexico, turning Teotihucan into a multiethnic settlement.
The intermediate elites used the arrival of workers from diverse regions for specialized work. Some of the skilled craftsmen gained status and economic power, the study found.
Residents of the Teopancazco neighborhood, some 500 meters (yards) from the city center, lived off heavy-duty jobs, squatting for hours for their manual labor. Their skeletal remains show signs of this hard work, she said.
These workers, the researcher said, "probably participated in the revolt of their administrators against the ruling elite."