Survivors of the Buchenwald (search) concentration camp joined German leaders Sunday to mark its liberation by U.S. troops 60 years ago and to warn that the suffering of its hundreds of thousands of prisoners must never be forgotten.

Some 240,000 prisoners passed through the camp just outside the city of Weimar (search) between 1937 and 1945 — Jews, Soviet prisoners of war, prominent political prisoners, Jehovah's witnesses and others. About 56,000 died, many worked to death by the Nazis.

About 1,000 people gathered in a cold drizzle as German Chancellor Gerhard Schroeder (search) and camp survivors observed a minute of silence and placed flowers where prisoners were forced to assemble.

Earlier, Schroeder expressed shame in Germany's name and honored the victims in a ceremony at Weimar's National Theater, a symbol of the city's classical cultural heritage.

"They fell victim to hunger, sickness, the sadistic terror and systematic murder," Schroeder said in a speech. "I bow before you, the victims and their families."

Though Buchenwald was not expressly built for mass killing, as Auschwitz was, it was just as much part of the Nazis' effort to wipe out anyone deemed un-German. Starvation, disease, overwork and medical experiments claimed many lives.

Jerry Hontas said he arrived as a 21-year-old Army medic the day after U.S. troops reached Buchenwald.

"It was so incredible — stacks of bodies, the smell, the total shock and confusion, people walking around by the thousands," he said. "We had no concept for this kind of insane cruelty."

By that time, Georg Sterner, a Hungarian Jew, had been at Buchenwald for 10 months. He recalled looking out from Barracks No. 37 when the first U.S. tank crashed through the barbed-wire perimeter fence on April 11, 1945.

"We always kept up hope," said the 77-year-old retired engineer from Budapest.

The official ceremony was part of a weekend of commemorations. It began with music by Ludwig van Beethoven, a representative of the cultured Germany of which Schroeder said the Nazis were "the absolute negation."

A women's choir sang a song written by two Austrian inmates at Buchenwald that became the secret camp anthem.

"Oh Buchenwald, I cannot forget you, because you are my destiny," they sang. "Only those who leave you can grasp how wonderful freedom is."

Former inmates recalled the stench of the crematoriums, the beatings and the forced labor. They worried that the world will find it harder to understand what happened under the Nazis once the survivors are gone.

"In a certain sense the cycle of active memory is closing, with the vow not only to cast our eyes back upon the past but also to look forward to the future," said Spanish writer and former culture minister Jorge Semprun, himself a former Buchenwald inmate.

With an eye on recent electoral successes by Germany's extreme-right fringe, Schroeder pledged that his country would remain vigilant against neo-Nazi stirrings.

Buchenwald inmates rose up against their Nazi captors as the 6th Armored Division of the U.S. 3rd Army approached the camp. When U.S. troops arrived, they found some 21,000 survivors. The Americans then forced Weimar residents to look at what had been going on about five miles outside their town. Some women reportedly fainted when they saw the piles of corpses.

But Schroeder noted that Buchenwald's sinister history continued after the Nazi defeat in World War II, when the Soviets turned it into a Stalinist prisoner camp where thousands died.

These days, Weimar would rather be remembered as the place where Johann Wolfgang Goethe, Germany's most revered classical writer and playwright, had his home. Goethe, who died in Weimar in 1832, walked in the forests where the Buchenwald camp later was built.

"This Weimar stands for humanity, enlightenment, idealism," Schroeder said. "It is the geographical closeness of culture and barbarism that makes us so speechless."