According to news reports, part of the as-yet-unnamed structure is badly damaged from the Crucifixion ceremony, which attracts as many as a million people.
The ceremony began in 1833 to give thanks for protection during a cholera epidemic. In the ritual a cross is raised and a man symbolizing Jesus is tied to it.
Sanchez, who announced the discovery Wednesday, said the pyramid site shows signs that it was used for ancient ceremonial purposes.
Miriam Advincula, a member of Sanchez's team, started to map the site in 2004 after ceramic fragments and ceremonial structures were discovered on the hillside. Exploratory excavations dug in 2005 and 2006 confirmed the find.
Out of respect for the current-day ritual, scheduled for next week, the archaeologists will limit further excavations.
"Both the pre-Hispanic structure and the Holy Week rituals are part of our cultural legacy, so we have to look for a way to protect both cultural values," Sanchez told the Associated Press.
Robertson, the Stanford anthropologist, said the discovery should provide information on people who began to settle outside of Teotihuacan in the later days of the civilization.
For long periods, he said, people only lived inside the ancient city, which was the size of 1500s London and was built about 2,000 years ago.
Some evidence suggests people began to resettle outside the city. But information on such a migration is spotty, he said.
"If this really is a big pyramid dated to the Teotihuacan period, it means there was an important enclave of elite Teotihuacanos living together," Robertson said. "That will be extremely important to us."
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