On September 22, Carlos Lalangui was digging a trench to make way for a natural gas pipeline on the outskirts of Lima in Peru when he spotted fragments of a human skull in the loosened soil.

“It was the first time I’d seen something like that,” said Lalangui, a worker with the natural gas company Cálidda. “But I knew it was a possibility.”

He stopped digging and notified his supervisor, who called in archaeologists. In a little more than a week, they had uncovered the remains of 21 people, eight of them children, who lived 600 to 800 years ago, said Cecilia Camargo, an archaeologist with the company.

Most had been buried in a classic pre-Columbian style: their bodies bound in a sitting foetal position and bundled in layers of textiles, surrounded by ceramic vessels, plates, pots and figurines.

The graves, discovered in a residential neighbourhood in Carabayllo, a district in northern Lima Province, were a reminder of Peru’s seemingly ubiquitous pre-Columbian cultural legacy, which continues to surface long after the Spanish conquest decimated the indigenous population.

In Lima, huacas — pyramid-like mounds of adobe brick that were once used as sacred and administrative centres — are the most visible reminder of the city’s ancient inhabitants. Dozens of ruins of huacas remain nestled among skyscrapers, middle-class neighbourhoods and shantytowns.

In recent years, ancient tombs and ceramics have been found during the expansion of the city’s airport and during the construction of a courthouse and a hydroelectric dam in towns nearby. Earlier this year, a resident of Lima called culture authorities to report funeral bundles he found while doing construction work on his house, said Yuri Castro, the culture ministry’s director of archaeological heritage.

Peru’s culture ministry has registered some 26,000 archaeological sites across the country. But budget constraints mean that only a fraction can be properly protected, Castro said. More than 1,100 sites are in Lima, a sprawling metropolis of 10 million people that has been occupied for more than 3,000 years.

“Those are only the sites that remain,” Castro said. “With the city’s expansion, they’ve gradually disappeared.”

Cálidda has made more than 1,500 archaeological findings in the nine years it has been laying natural gas pipelines across metropolitan Lima, said Camargo, and it employs a team of 30 archaeologists. “In Lima, 3,000 years of history are literally just beneath our feet,” she said. “We’ve made findings in nearly every district.”

“It’s a victory every time archaeologists can recover something responsibly and put it into the record,” said Daniel Sandweiss, the president of the Society for American Archaeology, who studies how pre-Columbian coastal societies in Peru adapted to climate change caused by El Nino. “Peru has the most fascinating pre-European records of any place in the Americas.”

John Villareal, another labourer at the site, said that when he was a boy, he dug up graves at a pre-Columbian burial ground in his village in northern Peru near the city of Chiclayo, working in 10-man teams with other labourers.

“Buyers would come from Chiclayo, and we’d sell the pieces for a pittance because we didn’t know what they were worth,” Villareal said. He recalled finding and trading masks, shell necklaces, gold pectorals and ceramic sculptures with erotic themes.

Most of the 21 people had been buried in a classic pre-Columbian style: their bodies bound in a sitting foetal position and bundled in layers of textiles

The newly uncovered graves were most likely part of a cemetery used for hundreds of years by different groups that farmed along the Chillón River, said Roberto Quispe, an archaeologist with Cálidda. Archaeologists first became aware of it after seeing aerial photos, taken in the 1940s, that showed the telltale signs of tomb raiding.

“You see some plots of farmland and next to them an empty lot that’s completely full of holes,” Quispe said. “The cemetery had been completely looted and people started to settle on top of it.”

The objects found in the graves correspond to the Chancay culture, which occupied an area north of Lima from 1200 to 1450 AD, and to an earlier cultural development known as Huaura. The unearthed items include a ceramic flute; a figurine perhaps representing a goddess; and an early version of a cuchimilco, a ceramic figurine with an expression of awe or surprise that was placed in Chancay tombs to accompany the dead.

Little is known about Chancay occupations this far south, Camargo said. Detailed studies of other skeletal remains in the area suggest that some populations may have been suffering from anaemia and health problems; large numbers of children have been found at some burial sites. “What was going on at that time?” Camargo asked. “Maybe those people were migrating.”

Most of the findings made by Cálidda during pipe laying are of pre-Columbian ceramics. But the company’s archaeologists have also found dozens of pre-Columbian graves, including 40 in a half-block in the heart of the city, and the remains of three Chinese indentured labourers who came to Peru in the 19th century and were buried near former agricultural plantations.

Also in the city’s centre, archaeologists have discovered abundant examples of a 2,000-year-old ceramic style known only as “white on red”. “It’s been studied so little that researchers still don’t refer to it as a culture,” Camargo said.

The gas company has opened community museums and exhibits in the districts where findings have been made so that residents can view them. “You can see how they connect it with their history,” Camargo said. “That connection, and that interest, is immediate.”

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