LIMA.- On Sept. 22, Carlos Lalangui was digging a trench to make way for a natural gas pipeline on the outskirts of this city when he spotted fragments of a human skull a dozen inches down 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 in Peru: their bodies bound in a sitting fetal position and bundled in layers of textiles, surrounded by ceramic vessels, plates, pots and figurines. One of the adults, thought to be a warrior, was found lain horizontally on reeds with a star-shaped mace of stone; the remains of a 2-year-old were found close by.

The graves, discovered in a residential neighborhood 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 — pyramidlike mounds of adobe brick that were once used as sacred and administrative centers — are the most visible reminder of the city’s ancient inhabitants. Dozens of ruins of huacas remain nestled among skyscrapers, middle-class neighborhoods 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 the city’s metropolitan area, 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.”

Before the Incan empire arose in the Andes in the 15th century, complex societies learned to thrive along Peru’s desert coast by irrigating fertile valleys and harvesting abundant fish stocks from the Pacific. Archaeologists hope that the new discovery can help shed light on those early cultures.

Today the coastal region is home to most of Peru’s population, and countless sites have already been lost to looting and development.

“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 laborer at the site, said that when he was a boy, he used to dig 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 laborers.

“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.

At the new site, he helped to carefully pack a skull to transport to a Cálidda lab for further investigation. “We would have discarded all of this,” Villareal said.

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.”

As Quispe worked inside a tomb, a restaurant nearby blasted cumbia music, and passersby stopped to watch and take pictures.

“I came to show my kids and nephews,” said Rolando Torres, a local resident, as children in school uniforms peered into one of the graves. A neighbor had sent Torres a video of the discovery, so he came right away to see the site. “We who live here, this is part of our ancestry,” he said.

The objects found in the graves correspond to the Chancay culture, which occupied an area north of Lima from A.D. 1200 to 1450, 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 anemia 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 laborers who came to Peru in the 19th century and were buried near former agricultural plantations.

Also in the city’s center, the 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.”

This article originally appeared in The New York Times.