RIO DE JANEIRO — Sailing from the Angolan coast across the Atlantic, the slave ships docked here in the 19th century at the huge stone wharf, delivering their human cargo to the “fattening houses” on Valongo Street. Foreign chroniclers described the depravity in the teeming slave market, including so-called boutiques selling emaciated and diseased African children.
The newly arrived slaves who died before they even started toiling in Brazil’s mines were hauled to a mass grave nearby, their corpses left to decay amid piles of garbage. As imperial plantations flourished, diggers at the Cemitério dos Pretos Novos — Cemetery of New Blacks — crushed the bones of the dead, making way for thousands of new cadavers.
Now, with construction crews tearing apart areas of Rio de Janeiro in the building spree ahead of this year’s World Cup and the 2016 Summer Olympics, stunning archaeological discoveries around the work sites are providing new insight into the city’s brutal distinction as a nerve center for the Atlantic slave trade.
But as developers press ahead in the surroundings of the unearthed slave port — with futuristic projects like the Museum of Tomorrow, costing about $100 million and designed in the shape of a fish by the Spanish architect Santiago Calatrava — the frenzied overhaul is setting off a debate over whether Rio is neglecting its past in the all-consuming rush to build its future.
“We’re finding archaeological sites of global importance, and probably far more extensive than what’s been excavated so far, but instead of prioritizing these discoveries our leaders are proceeding with their grotesque remaking of Rio,” said Sonia Rabello, a prominent legal scholar and former city councilwoman.
The city has installed plaques at the ruins of the slave port and a map of an African heritage circuit, which visitors can walk to see where the slave market once functioned. Still, scholars, activists and residents of the port argue that such moves are far too timid in comparison with the multibillion-dollar development projects taking hold.
Beyond the Museum of Tomorrow, which has been disparaged by critics as a costly venture drawing attention away from Rio’s complex history, developers are working on an array of other flashy projects, like a complex of skyscrapers branded in homage to Donald Trump and a gated community of villas for Olympic judges.
At the same time, descendants of African slaves who live as squatters in crumbling buildings around the old slave port are organizing in an effort to obtain titles for their homes, pitting them against a Franciscan order of the Roman Catholic Church that claims ownership of the properties.
“We know our rights,” said Luiz Torres, 50, a history teacher and leader in the property rights movement. With the slave market’s ruins near his home as testament, he added, “Everything that happened in Rio was shaped by the hand of blacks.”
Scholars say the scale of the slave trade here was staggering. Brazil received about 4.9 million slaves through the Atlantic trade, while mainland North America imported about 389,000 during the same period, according to the Trans-Atlantic Slave Trade Database, a project at Emory University.
Rio is believed to have imported more slaves than any other city in the Americas, outranking places like Charleston, S.C.; Kingston, Jamaica; and Salvador in northeast Brazil. Altogether, Rio received more than 1.8 million African slaves, or 21.5 percent of all slaves who landed in the Americas, said Mariana P. Candido, a historian at the University of Kansas.
Activists say the archaeological discoveries merit at least a museum and far more extensive excavations, pointing to projects elsewhere like the International Slavery Museum in the British port city Liverpool, where slave ships were prepared for voyages; the Old Slave Mart Museum in Charleston and Elmina Castle, a slave trading site on Ghana’s coast.
“The horrors committed here are a stain on our history,” said Tânia Andrade Lima, the chief archaeologist at the dig that exposed Valongo, built soon after Portugal’s prince regent, João VI, fled from Napoleon’s armies in 1808, transferring the seat of his empire to Rio from Lisbon.
The squalid wharf functioned until the 1840s, when officials buried it under more elegant docks designed to receive Brazil’s new empress from Europe. Both wharves were eventually buried under landfill and a residential port district, called Little Africa.
Many descendants of slaves settled where the slave market once functioned, with African languages spoken in the area into the 20th century. While the district is gaining recognition as a cradle of samba, one of Brazil’s most treasured musical traditions, it was long neglected by the authorities.
Black Consciousness Day is observed annually in Brazil on Nov. 20 to reflect on the injustices of slavery. In 2013 Ms. Rabello, the legal scholar, pointed out, Rio’s hard-charging mayor, Eduardo Paes, who is overseeing the biggest overhaul of the city in decades, did not attend the ceremony at Valongo, where residents began a campaign to have it recognized as a Unesco World Heritage site. Complicating the debate over how Rio’s past should be balanced alongside the city’s frenetic reconstruction, some families still live on top of the archaeological sites, occasionally excavating Brazil’s patrimony on their own.
“When I first saw the bones, I thought they were the result of a gruesome murder involving previous tenants,” said Ana de la Merced Guimarães, 56, the owner of a small pest control company who lives in an old house where workers doing a renovation first discovered remains from the mass grave in 1996.
It turned out Ms. Guimarães was living above a dumping ground for dead slaves that was used for decades, until around 1830. Estimates vary, but scholars say that as many as 20,000 people were buried in the grave, including many children.
Ms. Guimarães and her husband opted to stay in their property, opening a modest nonprofit organization on the premises, where visitors can view portions of the archaeological dig. The authorities have plans to build a light-rail project on their street, which may lead to more discoveries.
“This was a place of unspeakable crimes against humanity, but it’s also where we live,” Ms. Guimarães said in her home, complaining that public agencies had provided her organization with little support.
Washington Fajardo, a senior adviser to Rio’s mayor on urban planning issues, said that some important steps had been taken at the archaeological sites, including the designation of the slave port as an environmental protection area. And he said that a plan under consideration would create an urban archaeology laboratory where visitors could view archaeologists studying material from the sites.
Mr. Fajardo also emphasized that at another new venture in the port, the Rio Art Museum, residents of the area make up more than half the staff.
“We’d like to do more,” he said, referring to the slave cemetery. “It’s complex because there are people living on top of the site. If they want to stay, we have to respect their wishes.”
Throughout Rio, other discoveries are being made. Near the expansion of a subway line, researchers recently found relics belonging to Pedro II, Brazil’s last emperor before he was overthrown in 1889. And near the slave port, archaeologists found cannons thought to be part of a four-century-old marine defense system.
But none of the discoveries have been quite as striking as the unearthing of the Valongo wharf in 2011 and the earlier excavations of the cemetery under Ms. Guimarães’s home. Beyond the large stones of the wharf itself, archaeologists found items that helped reconstruct the daily lives of slaves, including copper pieces thought to be talismans and dominoes used for gambling.
Between the slave port and the cemetery, visitors can also view the Ladeira do Valongo, where the depots of Rio’s slave market once horrified foreign travelers. One visitor, Robert Walsh, a British clergyman who came to Brazil in 1828, wrote about the transactions.
“They are handled by the purchaser in different parts, exactly as I have seen butchers feeling a calf,” he said. “I sometimes saw groups of well-dressed females here, shopping for slaves, exactly as I have seen English ladies amusing themselves at our bazaars.”
Slavery’s legacy is clear across Brazil, where more than half of its 200 million people define themselves as black or mixed race, giving the nation more people of African descent than any other country outside Africa. In Rio, the large majority of slaves came from what is now Angola, said Walter Hawthorne, a historian at Michigan State University.
“Rio was a culturally vibrant African city,” Dr. Hawthorne said. “The foods people ate, the way they worshiped, how they dressed and more were to a large extent influenced by Angolan cultural norms.”
Brazil abolished slavery in 1888, making it the last country in the Americas to do so. Now the relatively relaxed approach to the archaeological discoveries is raising doubts about how willing the authorities are to revisit such aspects of Brazilian history.
“Archaeologists are exposing the foundations of our unequal society while we are witnessing a perverse attempt to remake the city into something resembling Miami or Dubai,” said Cláudio Lima Castro, an architect and scholar of urban planning. “We’re losing an opportunity to focus in detail on our past, and maybe even learn from it.”