German Chancellor Gerhard Schroeder has led a commemoration of the 60th anniversary of the liberation of the Nazis' Buchenwald death camp.
A choir sang the inmates' secret anthem for survivors
He urged the world never to forget the horrors perpetrated by the Nazis.
Survivors joined the ceremonies in eastern Germany where US troops freed 21,000 prisoners on 11 April 1945.
About 56,000 people died in Buchenwald, used to detain Jews, Soviet prisoners of war, Jehovah's Witnesses, political prisoners, homosexuals and many others.
Buchenwald - opened in 1937 - had no gas chambers as in the Auschwitz death camp, but prisoners were murdered by lethal injections or being shot, or were worked or starved to death.
"They fell victim to hunger, sickness, the sadistic terror and systematic murder," Mr Schroeder said in a speech.
"I bow before you, the victims and their families."
Some of the survivors, many of whom are now in their 80s, wore their prison uniform caps to the ceremony, where a choir sang a song written by two inmates that became a secret and unofficial anthem.
Inmates were worked, starved and tortured to death
The prisoners rose up against their guards as the US troops approached and about 21,000 were liberated, many in dire health.
The US commander was so horrified by what he found in Buchenwald that he forced the residents of nearby Weimar to visit and see what had been done in their name.
Mr Schroeder said: "We cannot change history, but this country can learn a lot from the deepest shame of our history."