Archeologists announced on Wednesday they have discovered a massive 6th-century Indian pyramid beneath a centuries-old Catholic religious site.

Built on a hillside by the mysterious Teotihuacan culture, the pyramid was abandoned almost 1,000 years before Christians began re-enacting the Crucifixion there in the 1800s.

"When they first saw us digging there, the local people just couldn't believe there was a pyramid," said archaeologist Jesus Sanchez. "It was only when the slopes and shapes of the pyramid, the floors with altars were found, that the finally believed us."

Ceramic fragments and the presence of other ceremonial structures on the hill suggested the possibility there was a pyramid or temple somewhere nearby, but the theory wasn't proved until a member of Sanchez's team, Miriam Advincula, started a project to map the site in 2004. Exploratory trenches dug in 2005 and 2006 confirmed the find.

"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," said Sanchez, who, along with archaeologist Miriam Advincula, has been exploring the site since 2004.

The people of Iztapalapa — now a low-income neighborhood plagued by squatter settlements — began re-enacting the Passion of Christ in 1833, to give thanks for divine protection during a cholera epidemic.

During the ritual, which draws as many as a million spectators every year, a wooden cross is raised just a few yards from the buried remains of the Teotihuacan temple, and a man chosen to portray Christ is tied to the cross.

Archeologists said they will fill in the excavation pits that revealed the pyramid to prevent the structure from being damaged by Good Friday spectators.

Measuring nearly 500 feet on each side, the 60-foot-tall pyramid was carved out on a natural hillside around 500 A.D., the scientists said. It was abandoned about 300 years later when the Teotihuacan culture collapsed.

Mexico abounds with cases in which Spanish conquerors literally built their Catholic faith atop the remains of older religions.

But the case of Iztapalapa hillside, known as the Hill of the Star, appears to be mere geographical coincidence, Sanchez said.

Pre-Hispanic cultures chose the hills that dot the otherwise flat, mountain-ringed Mexico Valley for their ceremonial sites, and postcolonial communities did the same.