Tooth analysis shows Africans taken from wide area ranging from Sudan in the north-east to Mozambique in the south

This article is more than 8 years old

This article is more than 8 years old

Locals called it the "cemetery of the new blacks", but in truth it wasn't much of a cemetery. Devoid of headstones, wreaths or tearful mourners, this squalid harbourside burial ground was the final resting place for thousands of Africans shipped into slavery.

The new world greeted them with a lonely death in an unfamiliar land.

For decades the cemetery and those buried there between 1760 and 1830 were forgotten, hidden under layer after layer of urban development.

But 15 years after the cemetery's fortuitous discovery – during the renovation of Petrucio and Ana de la Merced Guimaraes's family home when builders unearthed a series of muddy skeletons – academics now believe they have evidence of the true reach of the slave trade.

The study of teeth from 30 partial skeletons has hinted that slaves arriving in Rio – many of whom were sold on to work in coffee and sugar plantations or gold mines – came from a much wider geographical region than once thought.

Archaeologists and anthropologists studying bone and tooth fragments are shedding light on the horrors of a trade that saw at least 3 million slaves shipped from Africa to Brazil between 1550 and 1888, when the practice was officially abolished.

"It was ugly: a dump into which bodies were thrown and burned," said Sheila Mendonça de Souza, a bio-archaeologist studying the cemetery in Rio de Janeiro, once one of the busiest slave ports in the Americas.

"People weren't buried in tombs, they were tossed away into mass graves."

Della Cook, a biological anthropologist from the University of Indiana working on the burial ground, said: "There is a lot of scholarship on slave cemeteries and the slave trade in North America but very little in South America, which is one of the things that makes this site fascinating.

"We have historical records but we haven't been able to look before at the people themselves."

Using strontium isotope analyses of tooth enamel – a technique that helps detect where a person was raised and has previously been used on samples from burial sites in the Caribbean and Mexico – academics were able to confirm the large area from where the "new blacks" came.

"What we got was essentially the entire range of strontium isotope values," said Cook. "It surprised us that the spectrum was so broad."

The results indicated that slavers had "waded way into the interior" of Africa rather than restricting their search to coastal areas, Cook added.

Mendonça, who works for the national school of public health in Rio, said: "We were not able to pinpoint a specific place … but we confirmed the diversity of origin of those [slaves] who were arriving in Rio de Janeiro. They came both from the Atlantic coast and east coast."

A parallel study of cosmetic tooth modifications, common in some regions of Africa, also underlined the scope of the slave trade.

Mendonça said her team had found tooth markings indicating some of the slaves were native to what are now Sudan and Mozambique, in north-eastern and southern Africa.

Archaeologists believe as many as 20,000 slaves may have been buried at the cemetery, mostly men aged 18-25 who died during the gruelling journey to Brazil or shortly after arriving.

"The majority were very young, principally young boys and girls who would adapt better to captivity than older people," said Mendonça.

The dire conditions of the slave market and port, close to the cemetery, were captured by British writer Maria Graham, following a visit in the early 1820s.

"Almost every house in this very long street is a depot for slaves … In some places the poor creatures were lying on mats, evidently too sick to sit up," she wrote.

"The number of ships from Africa that I see constantly entering the harbour, and the multitudes that throng the slave-houses in this street, convince me that the importation must be very great. The ordinary proportion of deaths on the passage is, I am told, about one in five."

The 3 million slaves who made the journey were previously thought to have come only from what is now Nigeria and from the Portuguese colonies of Angola and Cape Verde.

Some fled, forming autonomous cities known as quilombos. Several of Rio de Janeiro's favelas – among them the Morro da Coroa, the Morro dos Prazeres and Pereirao – are thought to have begun life as quilombos.

With Rio undergoing a facelift for the 2016 Olympics, some archeological discoveries have been made as the city renovates its decrepit downtown port.

In early 2010 archeologists unearthed what they believe to be the remains of Rio's Valongo slave port, through which tens of thousands of African slaves were shipped. Experts hope advancing redevelopment projects will help them rescue further clues about the identities of Brazil's "new blacks", who were buried not far from the Valongo dock.

"When you start messing around with the landscape these things will appear," said Dr Ricardo Ventura Santos, a bio-anthropologist from Brazil's Oswaldo Cruz Foundation, who is co-ordinating the cemetery research team.

Cook said she hoped redevelopment would permit further excavation and the inclusion of places such as the slave burial ground on the city's tourist trail, creating a "monument to the African experience in Brazil".

The excavation of a Roman cemetery under London's Spitalfields market, during the 1990s, could serve as a model, she added.

"Rio has very little history of the slave trade for either Brazilians or external tourists," she said.