Carved into the earth and covered with a roof of reeds supported by shaped tree trunks, the 60-foot-long, oval chamber was discovered at the site of Pachacamac, about 20 miles south of the capital, Lima.
One of the largest Prehispanic sites in South America, Pachacamac was an important religious, ceremonial, political and economic center, consecrated to the god Pacha Camac.
The Inca Empire conquered the religious center less than a century before Spanish Conquistador Francisco Pizarro's brother, Hernando, plundered the site in 1533.
Within a few years of the conquest Pachacamac was completely abandoned.
Today, the impressive ruins make Pachacamac a candidate for inclusion on the list of UNESCO World Heritage sites.
The intact tomb was unearthed in front of the Temple of Pachacamac and had miraculously survived the pillaging of the colonial period.
A dozen newborn babies and infants were buried around the perimeter, with their heads oriented towards the tomb. The main chamber was divided into two sections, separated by a wall of mud bricks which served as a base for yet more burials.
Inside the chambers, the team of archaeologists from the Université libre de Bruxelles (ULB) found the remains of more than 70 skeletons and mummies, all in the characteristic fetal position and many still wrapped.
The burials represented both sexes and all ages, and were often accompanied by offerings which included ceramic vessels, dogs, guinea pigs, copper and gold alloy artefacts, and masks of painted wood.
Babies and very young infants were particularly common.
"The ratio adult/children is unusually elevated at this burial," archaeologist Peter Eeckhout, who has been carrying out fieldwork at the site for the past 20 years, told Discovery News.
"We have, at this stage, two hypotheses: human sacrifice or stocking of babies dead from natural causes, kept until their disposal in the tomb because of its special character," Eeckhout said.
Several individuals suffered mortal injuries, physical trauma or serious illness.
"One juvenile was killed by a blow on the skull. All over the cemetery we have lots of lethal disease traces, such as cancer and syphillis," Eeckhout said.
Indeed, Eeckhout's previous work at the site has revealed many diseases in the skeletal population, leading to the suggestion that Pachacamac was a sort of Prehispanic Lourdes. As testified by Inca sources, the affected individuals had travelled to the site in search of a cure.
Eeckhout and colleagues are confident that a dating of the skeletons and mummies, as well as bioarchaeological analysis, will answer the numerous questions that have arisen with the discovery.
"The tomb provides a wonderfully rich sample that will allow us to study possible kin ties, local or foreign origin of the deceased, health state, ritual and funerary customs," Eeckhout said.
"It will enlighten considerably our current knowledge on the material culture of the earliest phase of the Ychsma, the cultural group that lived in the Lima area before the Inca conquest," he said.
Photo: Skeletons and offerings in the tomb. Credit: Universite Libre de Bruxelles, Belgium.