Irish government investigators said Friday that up to 800 remains of babies have been discovered in a mass grave at a former Catholic home for unmarried mothers.

The discovery confirmed a local historian’s claim that the children may be in an unmarked grave at the former Bon Secours Mother and Baby Home in the western Irish town of Tuam.

Ireland’s Mother and Baby Homes Commission said excavations revealed an underground structure that contained “significant quantities of human remains.”

The commission said DNA analysis confirmed the ages of the children ranged from 35 weeks to three years. Records show the babies died between 1925 and 1961, the last year the home was open.

Burying the remains of babies in unmarked graves was a relatively common practice at Catholic-run homes in Ireland when there were high mortality rates in the early 20th century.

The government launched an investigation in 2014 after local historian Catherine Corless found death certificates for nearly 800 children who resided at the facility, but a burial record for only one baby.

“Everything pointed to this area being a mass grave,” Corless said. She recalled how boys playing in the area had reported seeing a pile of bones hidden in an underground chamber in the mid-1970s.

The Catholic church operated many of Ireland’s social services in the 20th century. Some housed tens of thousands of unmarried pregnant women, including rape victims.

Unmarried women and their babies were then viewed as a stain on Ireland’s reputation as a fervently-Catholic country.

The fathers of some of the babies were powerful figures, such as priests, the wealthy, and married men.

The Minister for Children and Youth Affairs, Katherine Zappone, said the news was “sad and disturbing.” She added that an investigation would continue and a decision would be made to determine what should happen with the remains.