The cases expose a dark chapter in Canada's history and are among several burial sites unearthed elsewhere in the last decade that exposed long-hidden horrors.

Canada's indigenous children

The latest discovery of 751 unmarked graves in Canada involves the former Marieval residential school in eastern Saskatchewan that had hosted indigenous children between 1899 and 1997 before being demolished.

"This is not a mass grave site. These are unmarked graves," Cowessess First Nation Chief Cadmus Delorme told reporters.

It comes just weeks after the nation was rocked by the discovery of the remains of 215 schoolchildren at another former indigenous residential school in Kamloops, British Columbia.

Some 150,000 Native American, Metis and Inuit children were forcibly enrolled up until the 1990s in 139 such schools in Canada, where they were isolated from their families, language and culture, and physically and sexually abused by staff and teachers.

More than 4,000 students died in the schools, according to a commission of inquiry that concluded Canada had committed "cultural genocide" against indigenous communities. 

Spain's Valley of the Fallen

The Spanish government in March approved a special fund to exhume graves at the Valley of the Fallen, a vast complex near Madrid where some 33,000 victims of the Spanish Civil War are buried.

Built between 1940 and 1958 partly by the forced labour of political prisoners, the imposing basilica and mausoleum were initially intended for those who had fought for the fascist dictator General Franco.

But in 1959 the remains of many Republican opponents were moved there from cemeteries and mass graves across the country without their families being informed.

When Franco died in 1975, authorities opted to draw a veil over the past for fear of further conflict.

Socialist Prime Minister Pedro Sanchez has made the rehabilitation of Franco's victims a priority since coming to power in 2018.

Campaigners estimate that more than 100,000 dead from the war and its aftermath remain buried in unmarked graves across Spain -- a figure exceeded only by Cambodia, says Amnesty International.

Ireland's care homes horror

In January a six-year-long enquiry concluded that 9,000 children had died in state- and Catholic Church-run homes for unmarried women and their babies in Ireland that were still operating as recently as 1998.

The Commission of Investigation into Mother and Baby Homes was established in 2015 after an amateur historian uncovered evidence of a mass grave of infants at one such home in the town of Tuam.

Catherine Corless proved that 796 children, from newborns to a nine-year-old, died at the home run by Catholic nuns between 1925 and 1961.

There are no burial records, leading many to believe a mass grave in a disused septic tank discovered in 1975 near the home was the children's final resting place.

Plans are under way to excavate the site.

Aborigines island burial site

Three unmarked burial sites on Australia's World Heritage-listed Fraser Island were uncovered in 2014. They are believed to be of people from the Aboriginal community who died at the Bogimbah Creek mission established there in 1897.

More than 100 Aboriginals are thought to have died at the site where they were separated from their families. Living conditions were appalling, and many succumbed to diseases or malnutrition before it was abandoned in 1904.

Aboriginals are still the most disadvantaged Australians, with higher rates of poverty, ill health and imprisonment than any other community.