It has long been a matter of contention: Was the Aztec and Mayan practice of human sacrifice as widespread and horrifying as the history books say? Or did the Spanish conquerors overstate it to make the Indians look primitive?
In recent years archeologists have uncovered mounting physical evidence that corroborates the Spanish accounts in substance, if not number.
Using high-tech forensic tools, archeologists are proving that pre-Hispanic sacrifices often involved children and a broad array of intentionally brutal killing methods.
For decades, many researchers believed Spanish accounts from the 16th and 17th centuries were biased to denigrate Indian cultures. Others argued that sacrifices were largely confined to captured warriors. Still others conceded the Aztecs were bloody, but believed the Maya were less so.
"We now have the physical evidence to corroborate the written and pictorial record," said archeologist Leonardo Lopez Lujan. "Some 'pro-Indian' currents had always denied this had happened. They said the texts must be lying."
The Spaniards probably did exaggerate the number of victims to justify their war against idolatry, said David Carrasco, a Harvard Divinity School expert on Mesoamerican religion.
But there is less doubt about the nature of the killings. Indian pictorial texts known as "codices," as well as Spanish accounts of the time, quote Indians as describing multiple forms of brutal human sacrifice.
Victims had their hearts cut out or were decapitated, shot full of arrows, clawed, sliced, stoned, crushed, skinned, buried alive or tossed from the tops of temples.
Children were said to be frequent victims, in part because they were considered pure and unspoiled.
"Many people said, 'We can't trust these codices because the Spaniards were describing all these horrible things,' which in the long run we are confirming," said Carmen Pijoan, a forensic anthropologist who found some of the first direct evidence of cannibalism in a pre-Aztec culture more than a decade ago: bones with butcher-like cut marks.
In December, at an excavation in an Aztec-era community in Ecatepec, just north of Mexico City, archeologist Nadia Velez Saldana described finding evidence of human sacrifice associated with the god of death.
"The sacrifice involved burning or partially burning victims," Velez Saldana said. "We found a burial pit with the skeletal remains of four children who were partially burned, and the remains of four other children that were completely carbonized."
Although the remains don't show whether the victims were burned alive, there are depictions of people -- apparently alive -- being held down as they were burned.
The dig turned up other clues to support descriptions of sacrifices in the Magliabecchi codex, a pictorial account painted between 1600 and 1650 that includes human body parts stuffed into cooking dishes, and people sitting around eating, as the god of death looks on.
"We have found cooking dishes just like that," said archeologist Luis Manuel Gamboa. "And, next to some full skeletons, we found some incomplete, segmented human bones." Researchers don't know if those remains were cannibalized.
In 2002, government archeologist Juan Alberto Roman Berrelleza announced the results of forensic testing on the bones of 42 children, mostly boys around age 6, sacrificed at Mexico City's Templo Mayor, the Aztecs' main religious site, during a drought.
All shared one feature: serious cavities, abscesses or bone infections painful enough to make them cry.
"It was considered a good omen if they cried a lot at the time of sacrifice," which was probably done by slitting their throats, Roman Berrelleza said.
The Maya, whose culture peaked farther east about 400 years before the Aztecs founded Mexico City in 1325, had a similar taste for sacrifice, Harvard University anthropologist David Stuart wrote in a 2003 article.
In the late 19th and early 20th century, "The first researchers tried to make a distinction between the 'peaceful' Maya and the 'brutal' cultures of central Mexico," Stuart wrote. "They even tried to say human sacrifice was rare among the Maya."
But in carvings and mural paintings, he said, "we have now found more and greater similarities between the Aztecs and Mayas," including a Maya ceremony in which a costumed priest is shown pulling the entrails from a bound and apparently living sacrificial victim.
Some Spanish-era texts have yet to be corroborated with physical remains. They describe Aztec priests sacrificing children and adults by sealing them in caves or drowning them. But the assumption now is that the texts appear trustworthy, said Lopez Lujan, who also works at the Templo Mayor site.
For Lopez Lujan, confirmation has come in the form of advanced chemical tests on the stucco floors of Aztec temples, which were found to have been soaked with iron, albumen and genetic material consistent with human blood.
"It's now a question of quantity," said Lopez Lujan, who thinks the Spaniards -- and Indian picture-book scribes working under their control -- exaggerated the number of sacrifice victims, claiming in one case that 80,400 people were sacrificed at a temple inauguration in 1487.
"We're not finding anywhere near that ... even if we added some zeros," Lopez Lujan said.
Researchers have largely discarded the old theory that sacrifice and cannibalism were motivated by a protein shortage in the Aztec diet, although some still believe it may have been a method of population control.
Pre-Hispanic cultures believed the world would end if the sacrifices were not performed. Sacrificial victims, meanwhile, were often treated as gods before being killed.
"It is really very difficult for us to conceive," Pijoan said of the sacrifices. "It was almost an honor for them."