Germany will inaugurate the first national memorial to the estimated 300,000 ill and disabled people systematically murdered by the Nazis on Tuesday, at a ceremony with victims' relatives.
The site next to the Tiergarten park is the fourth and likely final major memorial in Berlin's city centre to groups targeted in the Holocaust, following monuments dedicated over the last decade to Jewish, gay and Roma victims.
It honours a long-neglected class of people with few vocal advocates in a move historians say is long overdue.
Uwe Neumaerker, director of the Holocaust memorial foundation in Berlin, said the slaughter of patients and residents of care homes marked "the first systematic mass crime of the National Socialist regime".
"It is considered a forerunner of the extermination of European Jews," he said.
The German parliament voted in November 2011 to erect a memorial to the victims of the Nazis' cynically labelled "euthanasia" programme adjacent to Berlin's renowned Philharmonie concert hall.
It includes a wall-like sculpture made of blue glass and information panels detailing the Nazis' campaign to exterminate the sick, the physically and mentally handicapped, those with learning disabilities, and people branded social "misfits".
The memorial is on the site of a now-demolished elegant villa at Tiergartenstrasse 4 where more than 60 Nazi bureaucrats and like-minded doctors worked in secret under the "T4" programme to organise the mass murder of sanatorium and psychiatric hospital patients deemed unworthy to live.