Pope Francis is slated to arrive in Canada on Sunday to apologize for historical abuse inflicted upon indigenous children by leaders at Catholic-run residential schools.

He is scheduled to land in Alberta at around 11:20 a.m. to kick off what he calls a “pilgrimage of penance.” Francis will make two more stops in Canada, also visiting Quebec City and Iqaluit.

Free tickets for the event were claimed shortly after being made available, according to the trip’s organizer, the Canadian Conference of Catholic Bishops.

POPE FRANCIS WARNS GERMAN BISHOPS: CHANGING TEACHINGS IS ‘NOT LAWFUL,’ CAUSES CHURCHES TO ‘ROT AND DIE’

Thousands of the tickets were reserved for indigenous survivors of the residential schools. Indigenous leaders in Treaty 6, the location Francis is visiting in Alberta, have said they were overwhelmed with requests from survivors who wish to attend the event.

More than 150,000 indigenous children were separated from their families and brought to residential schools between 1881 and 1996. A number of children were allegedly starved, beaten and sexually abused.

POPE DERIDES BIDEN’S ABORTION VIEWS, CATHOLIC SELF-IDENTITY AS ‘INCOHERENCE’

Canadian leaders have been aware of the many children dying at the schools since 1907, but the incidents garnered more attention following last year’s discoveries of what appeared to be unmarked graves at or near former residential schools.

Pope Francis then apologized for the role the Catholic Church played in the schools earlier this year when indigenous delegates visited the Vatican before heading to Canada. 

POPE FRANCIS DISMISSES RUMORS ABOUT RESIGNING, SAYS HE WANTS TO VISIT MOSCOW, KYIV

But some survivors and indigenous leaders say an apology is not enough.

Demands have been made for financial compensation, the return of indigenous artifacts, the publication of school records, support for an accused abuser’s extradition and the repeal of a doctrine from the 15th Century that defended colonial dispossession of indigenous people through a papal bull, or edict.

Reuters contributed to this report.