Construction workers in Bolivia have stumbled upon a mass grave containing the remains of hundreds of people, likely indigenous miners who died during the Spanish colonial era, a researcher has said.
The workers found the remains this week as they started construction on a new building in the "El Minero" district of Potosi, located high in the Andes.
"We are talking about a common grave found at about 1.8 metres, and the human remains are scattered over an area of four by four metres," said Sergio Fidel, a researcher at a museum belonging to Tomas Frias University on Saturday.
In the Spanish colonial era, Potosi became famous for its massive silver and tin reserves, which started to be mined in the 16th century.
Local indigenous people, mainly ethnic Aymara, were commonly put to work as both slaves and indentured servants, especially at the famed Cerro Rico (Rich Hill) mountain.
The construction workers, who have had no specialised excavation training, said they found the remains of 400 to 500 people and that there might be many more.
The university got involved when its staff learned the workers were piling the bones in a massive heap, fully exposed as construction continued.
One theory is that they stumbled on an indigenous burial ground of slaves and indentured servants who would have worked at the mine in precarious conditions, said Jose Antonio Fuertes, a historian at the national mint.
Another possibility is the remains could be linked to the collapse of a reservoir in Potosi during the 1600s, which killed some 2,000 people.
The Andean city, once among the world's largest, now has a population of 200,000.
Last month, UNESCO placed the city and the increasingly unstable Cerro Rico on its World Heritage in Danger list due to "uncontrolled mining operations".