Scientists have discovered tombs filled with up to 40 mummies, each around a 1,200 year old ceremonial site in Peru's Cotahuasi Valley. Thus far, archaeologists have excavated seven tombs containing at least 171 mummies in an area now called Tenahaha.

The tombs are located on small hills surrounding the site. "The dead, likely numbering in the low thousands, towered over the living," wrote archaeologist Justin Jennings, a curator at Toronto's Royal Ontario Museum, in a chapter of the newly published book "Tenahaha and the Wari State: A View of the Middle Horizon from the Cotahuasi Valley"

Before rigor mortis set in, the mummies had their knees put up to the level of their shoulders and their arms folded along their chest, the researchers said. They were then bound with rope and covered in textiles. The mummies range in age from neonate fetuses to older adults, with some of the youngest infants being buried in jars.

The mummified remains were in poor condition due to damage from both water and rodents. Researchers also found that some of the remains had been intentionally broken apart with their bones scattered across the tombs.

"Though many individuals were broken apart, others were left intact," Jennings wrote in the book. "People were moved around the tombs, but they sometimes remained bunched together, and even earth or rocks were used to separate some groups and individuals." Some grave goods were smashed apart, while others were left intact, he said.

Understanding the selective destruction of the mummies and artifacts is a challenge. "In the Andes, death is a process, it's not as if you bury someone and you're done," Jennings told Live Science in an interview.

"The breakup of the body, so anathema to many later groups in the Andes, would have been a powerful symbol of communitas (a community of equals)," wrote Jennings in the book. However, while this idea helps explain why some mummies were broken up, it doesn't explain why other mummies were left intact, Jennings added.

Radiocarbon dates and pottery analysis indicates the site was in use between A.D. 800 and A.D. 1000, with the Inca rebuilding part of the area at a later date.

Research also shows that this time Peru was undergoing tumultuous change with growing populations, agriculture expansion and growing class divisions. Archaeologists also found evidence of violence with many bodies showing signs of cranial trauma. At Tenahaha, however, there was little evidence of violence against humans, with most of the decorations depicted happy people smiling. Scientists believe the location could have been a type of "neutral ground," where people could meet to bury their dead and feast.

"It's a period of great change and one of the ways which humans around the world deal with that is through violence," Jennings said in the interview. "What we are suggesting is that Tenahaha was placed in part to deal with those changes, to find a way outside of violence, to deal with periods of radical cultural change."