Two statues and architectural details at the site indicate that the inhabitants of Zazacatla adopted Olmec styles when they changed from a simple, egalitarian society to a more complex, hierarchical one, archaeologist Giselle Canto told the Associated Press.
"When their society became stratified, the new rulers needed emblems to justify their rule over people who used to be their equals," Canto said of Zazacatla's inhabitants.
The Olmec's influence can be seen farther afield than their traditional area of control, including other cultures' ceremonial-center layouts and artworks, said John Machado, a pre-Columbian art historian at Chaffey College in Rancho Cucamonga, California.
"The Olmec need for materials—especially the precious and ritually important jade—developed a broad trade network," Machado said.
"Evidence of this interaction has been discovered as much as 400 miles [640 kilometers] in Guerrero," a state on Mexico's Pacific coast that is just south of Morelos state.
Numerous Olmec-style rock carvings and statues have been found at Chalcatzingo, a non-Olmec settlement in the eastern part of Morelos state that thrived from about 700 B.C. to 500 B.C.
"However, western Morelos seemed unaffected by such contacts and in fact seemed a backwater during the 900-to-500-B.C. time period," said Grove, the University of Illinois professor emeritus.
"The Zazacatla discoveries change that whole scenario completely," he said. "It now seems that settlements in western Morelos were also involved" with the Olmec.
Zazacatla covered less than 1 square mile (2.6 square kilometers) between 800 and 500 B.C.
The excavation of the site began last year. Since then archaeologists have unearthed six buildings and two sculptures of what appear to be Olmec-style priests, the Associated Press reports.
But much of the site remains buried under housing developments, a gas station, a highway, and a commercial building.
Grove said Mexico doesn't have financial resources for extensive archaeological explorations.
"The forces of modernization" destroy hundreds, maybe even thousands, of unexplored sites every year, he speculated.
"For most of the country there is still a great knowledge void," Grove said. "The further you get from major towns and major highways, the less is known."
"It is usually only serendipitous when building activities bring to light a significant site such as Zazacatla and archaeologists are contacted and are able to study the discovery."
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