The ruins aren't particularly impressive, just some stone and clay footings for houses that probably supported walls of wood or clay wattle. And it's that very ordinariness that has experts excited.
The remnants being uncovered in the hills east of Mexico City at a spot known as Amecameca are from an ancient neighborhood _ a home to regular folks.
"What makes this important is that it is a residential area, not a ceremonial or religious site," said Felipe Echenique, a historian for the National Institute of Anthropology and History, or INAH, which is in charge of reviewing the site.
"In Mexico, we really have very little evidence of how the cities really were, or how people lived," said Echenique, who was not involved in the dig but is familiar with preliminary findings.
Towering pyramids in Mexico like Chichen Itza or temple complexes like Uxmal are well known, but the vast urban centers that supported those ceremonial centers largely disappeared.
The housing compounds at Amecameca were apparently built by one of the still-unnamed cultures that populated the Valley of Mexico long before the Aztecs appeared in the area in 1325 and founded Tenochtitlan, the precursor to Mexico City.
Rebeca Lopez Reyes, an activist with the preservationist group Guardians of the Volcanos that helped stop roadwork that was damaging the site, said researchers for INAH have found ceramic pots and bones. And, she said, there is a stone serpent's head, suggesting that the god Quetzacoatl, "the Feathered Serpent," may have been worshipped there centuries before the Aztecs paid him homage.
The institute has not released a formal report on what was found, saying researchers need more time.
The few excavations of residential areas carried out so far in Mexico have yielded fascinating details.
In Teotihuacan, one of the biggest pre-Hispanic cities located northeast of Mexico City, some houses appear to have been illuminated by narrow doorways that opened onto central patios with shallow pools that acted as "water mirrors" to direct light inside the rooms. Techniques for building windows were apparently not yet known.
Investigators say similar discoveries could emerge from Amecameca, where so far only about 120 square yards (meters) of an estimated 5-acre (2-hectare) site have been excavated.
"In what has been excavated so far ... there some strange settlement patterns that are emerging," said Echenique.
For example, between one housing compound and another, researchers found an empty area that contained no relics _ something that would be unusual in a densely populated area unless it was a border between neighborhoods, a street, or the site of a long-vanished wood structure.
Perhaps the most unusual thing is that local residents were the ones who noted the relics and called in researchers _ after setting up a protest camp to block backhoes from tearing up more of the area for a planned highway.
"The inhabitants of Amecameca were more or less following the work on the roadway, and when they saw that there were a lot of relics coming up, they notified the institute," Echenique said.
Progress has often trumped history in Mexico, where roads have regularly been pushed through ruins.
In Mexico City, the lava-buried remains of the ancient Cuicuilco culture, with its famed round pyramid, are crowded and partly covered by shopping malls, housing developments, a major freeway and even a college for archaeologists.
The Amecameca protesters now guard against construction workers and looters and to explain the ruins to passers-by. They are asking the road be rerouted.
"The planned route wouldn't have to be changed that much," Lopez Reyes said.
Authorities have not yet commented on the demands, and the builders of the road, known as the Mexican Beltway, did not respond to requests for comment. Both federal and state transportation officials declined to comment.
INAH spokesman Arturo Mendez said that "in almost every project of this type, there are going to be discoveries" of pre-Hispanic material." Thousands of years of settlement have left potentially interesting relics scattered across the region.
The institute normally sends in a team to excavate, recover any significant items, carefully rebury the site for possible future exploration, and then allow construction to continue.
The people of Amecameca say they want to prevent that from happening to them.
Maria de los Angeles Eusebio, 55, a retired anthropologist, is one of the residents who have camped out for the last week to prevent construction machinery from going through. Equipped with tents, coffee "and lots and lots of blankets," the protesters are staying day and night, through wind, rain and cold, to ensure the remains of their ancestors' city aren't destroyed.
"We don't want them to just bury this and run the highway over the top of it," said Eusebio. "We want them to return the artifacts, so we can display them in a museum for the community."