In an abandoned train depot near Rio de Janeiro's derelict port area are stacked dozens of black plastic boxes. Two young researchers are sorting through their contents. Inside one box: a ceramic pipe. Inside another: a plate used in a traditional religious ceremony.

All of the objects belonged to former slaves and most of these finds wouldn't have been discovered if it hadn't been for work related to the Olympics.

In 2011, the city of Rio embarked on an extensive project to rejuvenate the long-neglected port area. Among the planned projects: the Museum of Tomorrow, an Olympic village for judges, light rail to carry the tourists expected during the Games, as well as better housing for the area's residents.

To their surprise, they began unearthing hundreds of artifacts dating from the early 1800s.

"These objects prove the existence, the materialization of this terrible process in the human history — the history of the slave," says Claudio Honorato, a historian with the New Blacks Institute for Research and Memory.

I meet Honorato at a spot rife with historical import: the Valongo Wharf, where close to half-a-million slaves were off-loaded during Brazil's slave trade. It was built in 1811, then later buried, only to be unearthed again during a $2-billion excavation project.

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Olympic-related renovations that began in 2011 unearthed Valongo Wharf and hundreds of artifacts from Rio's slave past. Advocates are hoping to use the archeological finds to turn the area into an important tourist attraction. (Kim Brunhuber/CBC)

"The development work was really to be done faster but they had to stop the process," Honorato says. "The Museum of Tomorrow and the Mauá Pier were expected to be opened in 2011 with a big party and were only opened now. When they came upon all the African-Brazilian materials — these archeological traces — the development work had to stop."

That's because developers have to comply with legislation passed in Rio relatively recently that says no development can go ahead on land where evidence of historical interest has been discovered, without doing further archeological research.

"This port area was a place where a lot of ships from Africa came, bringing 500,000 slaves," says Ondemar Dias, with the Brazilian Archeological Institute. "The amount of materials related to these cultures demonstrates, along with other research, that it's a very important place to tell the story of this culture that came to Brazil."  

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Claudio Honorato is a historian with the New Blacks Institute for Research and Memory. He says African history has rarely been valued in Brazil.

That story rests in a warehouse that's almost impossible to get to. All the roads around it, save one, are being ripped up and repaired as a result of the very renovations that unearthed the treasures now being studied by the archeologists inside. Almost none of them have been seen by the general public. 

One of the researchers opens a box, unwraps the plastic and pulls out several broken wooden handles. "This is a Bantu spatula from Angola," she says, pointing to markings engraved in the wood. "With this mark, you can define what group came from where."

Next she pulls out three cow femurs. Once they're turned right-side up, the holes form faces carved in the bone. "The faces are used in their religious ceremonies," she says.

She then shows me what looks like a small metal ring.

"In the Condomblé — the African religion — they put these on their arms," she says. "But because when they came here, they couldn't express their religion, they would put it on their fingers to protect themselves from spirits."

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Many slaves used to wear armbands to protect themselves from evil spirits. But they were forbidden from doing so by their slave owners. So, archeologists say, the slaves made them into rings and wore them on their fingers instead. (Kim Brunhuber/CBC)

The objects recovered from the port area, says Honorato, differ from those discovered elsewhere.

"We have lots of objects in the museums here that are, for instance, gifts of African embassies to our emperor, and even other objects that were conquered in wars in Africa," Honorato says. "These, on the other hand, were objects built here. They are part of the culture of these individuals who lived in this society, who contributed to this society. 

"I think this is a material that reveals the day-to-day life, the common life, in the places that these Africans lived, where they've worked, where they've celebrated. And that's why we call this the 'slavery paths in Rio de Janeiro.' It reveals the aspects of this 'Little Africa' — what they were actually doing in their daily life."

African history, he says, has rarely been valued in Brazil. At other sites of historical importance, discoveries have been quietly covered up to enable construction to continue. But now advocates are hoping to turn the area's African history into an important tourist attraction.

"That's why Brazil is requesting that this place go on the World Heritage list," Dias says.

There are already tours incorporating the area's African history, including an area where the bodies of dead slaves were dumped. Honorato says he hopes this will lead to a change in attitudes; that African history will no longer be buried, like the Valongo Wharf.

"[It's important] to preserve this history, to preserve this culture, this memory," he says. "And also ensure the memory of those who resisted, and are here, until the present moment."