Taking small steps, archaeologist Jesús Sánchez points out hand-carved rocks jutting out from a hill overlooking Mexico City's crowded, working-class neighborhood of Iztapalapa. "Look at this one, and then this one," he says, singling out volcanic rock from angular stone. "Do you see how the stones form a line? That's one of the pyramid's three levels."
What Mr. Sánchez is tracing is a newly discovered, 1,500-year-old pyramid built by the Teotihuacán culture, which also constructed the famous pyramids about an hour's drive northeast of the city. The base is the size of Teotihuacán's huge Pyramid of the Moon, about 500-feet wide, and the whole structure is about 60-feet tall.
The discovery has archeology circles abuzz. "It's a fantastic find," says archeologist and Teotihuacán expert George Cowgill of Arizona State University in Tempe. "It's no exaggeration - not hype at all - to say that this rewrites our picture of the whole Teotihuacán era."
One catch: The major archeological find may never see daylight.
Every year, the hill covering the pyramid attracts more than a million pilgrims on Good Friday to watch a theatric re-enactment of the crucifixion of Christ.
The pyramid's discovery has excited residents, but also raised a dilemma over how to accommodate two of Mexico's most important cultural traditions without trampling on either of them, nor on the poor squatters and small businessmen who live and work around the site.
Pre-Hispanic researchers have faced similar struggles in Mexico, when their projects clash with sites of Catholic importance. Notably, archeologists have yet to fully excavate the Aztec's holiest temple because Mexico City's colonial-era cathedral sits on top of it. Yet they did convince the government to clear away several buildings to allow for digging. It's unclear how much pull archeologists will have with their latest claim.
"In no way do we think our find should be valued more than the Holy Week traditions," says Myriam Advincula, one of the site's lead archeologists. "But we also feel an urgency to restore and protect the area."
The bloody, lifelike Good Friday tradition, which involves an actor portraying Christ hanged from a hilltop cross, dates back to the 1830s and began when locals expressed gratitude for the end to the plague. It is one of Latin America's best-known Holy Week rituals. For years, Catholics attending the event were unaware that the newer tradition took place over a Teotihuacán ritual site.
Those in charge of the Passion of Christ production greet the pyramid as cultural patrimony that unites Mexico's past and present.
"We must now agree on whether we should put limits on a Catholic ritual," says Roberto Guillén, head of the re-enactment event. "I'm not sure how we'll work that out."
Catholic devotees who flock to the hill for the re-enactment take a toll on the pyramid's site, archeologists worry. Further, event organizers construct platforms on the hillside to accommodate TV crews and stadium-style audio systems.
For now, archeologists are erecting a periphery fence. After Easter, they'll launch a public education campaign in the nearby neighborhoods, focusing on the pyramid and the area's pre-Columbian roots.
Next, archeologists will lobby the community for more far-reaching and permanent conservation measures, perhaps keeping next year's Good Friday attendees from ascending the hill. However, this would keep pilgrims from fully experiencing the visceral struggle of the actor who must haul his 40-pound cross up the hill.
In exchange for the restrictions, the scientists would develop a tourism project on the hill that could provide a more stable, year-round income for local residents. The site would probably draw mostly Mexicans and some intrepid foreigners willing to brave this rough part of town.
"Now that we know this pyramid exists, we can't have the same attitude toward this space as before," says Sánchez, who works at Mexico's National Institute of Anthropology and History. "This site can provide new pieces to a puzzling part of Mexico's history. It must be recognized that something else stood here before."
Until now, past research concluded that no major Teotihuacán settlements existed beyond the ancient city that houses the Pyramid of the Sun and Moon. Also, the newly discovered pyramid, abandoned when the Teotihuacán culture fell around 800 A.D., was apparently refortified by the legendary Toltec civilization, predecessors of the Aztecs. The dig may offer critical clues to a 2,000-year-old Teotihuacán culture that left little trace of its origin, language, or rulers.
The discovery's grandeur intrigues local residents. But tension may rise among some residents if archeologists push for the area's conservation. Squatter shacks, along with more established houses, sprawl over the pyramid site.
Rumors of relocating homes are circulating.
"It's incredible to think that something so old and huge is beneath my living room floor," says Alberto Anaya, a mechanic who lives only yards from the pyramid site. "I still don't believe it. But does that mean I have to give up my home?"
Meantime, Mr. Anaya depends on the Easter Week rituals for extra cash. He and his neighbor, Francisco Javier Balois, sell ice to visitors. Sales were already brisk as buses transported tourists wanting a look at the preritual preparations. "It'll be nonstop business," says Mr. Balois.