Weimar, Germany (AP) — Buchenwald survivor Henry Oster recalls thinking that a fellow inmate had "lost his sense of reality" when he said 70 years ago Saturday that the concentration camp was being liberated, bringing an end to the long ordeal of the 21,000 surviving prisoners.

Oster, 86, visited the site near the German city of Weimar for the first time since its liberation on April 11, 1945 — one of a group of survivors and veterans who came to mark the anniversary of the liberation. Buchenwald was the first major concentration camp entered by American forces at the end of World War II.

"What I see here, where the barracks used to be, at every barrack there was a pile of dead bodies, this is in your memory forever," Oster said. "When someone asks how Buchenwald was, you immediately see the dead bodies again."

Around 250,000 prisoners in total were held at Buchenwald from its opening in July 1937 to its liberation. An estimated 56,000 people were killed, including political prisoners, people dubbed "asocial" by the Nazis, Soviet prisoners of war, Sinti and Roma, and approximately 11,000 Jews.

Oster, a Jewish German born in Cologne, was taken to the Lodz ghetto in occupied Poland in 1941 and later to the Auschwitz-Birkenau death camp. His father died of starvation and his mother was gassed on the day they arrived at Auschwitz, he said.

In January 1945, Oster was sent on a "death march" to Buchenwald as the Nazis forced inmates westward in the face of advancing Soviet forces.

Entering the former camp through the wrought-iron gate that bears the words "Jedem das Seine" — "To each his own" — with its clock stopped at 3.15, the time of the liberation, Oster recalled that moment.

"We had no idea the Allies were in Europe, and when we heard noises at about a quarter past three, we looked out of the window — which took a great effort — and one of my friends said with a weak voice 'I think we are getting liberated,'" Oster said. "And we thought he had lost his sense of reality like so many people there."

Oster was taken to an orphanage in France and emigrated to the United States in 1946. He now lives in Woodland Hills, Calif.

A minute of silence was held Saturday afternoon at the tree-ringed hilltop site's former assembly ground, bringing together former inmates and liberators — on whom Buchenwald also left an indelible impression.

James Anderson, a 91-year-old from Indianapolis, went in as an Army medic on that day and recalled that many prisoners were so weak they could no longer move.

"The devastation was so tremendous," Anderson said, his voice trembling. "I was a ... kid, and to see this it was hard for me to believe this was actually happening, you know, and the prisoners were so glad to see us, they would hug us and everything."

Robert Harmon, then a private serving in Gen. George S. Patton's Third Army, was deployed in Weimar and first saw Buchenwald survivors a few days after the camp's liberation.

"They had these thin pyjama clothes, they had terrible food, you can imagine, and of course the men had not shaven forever, and they just looked awful," said Harmon, from Seattle, who turns 90 today.

"They were stunned psychologically, they were so afraid of authority that they were very careful about speaking to us, but they were so hungry that they dared, and that was such an act of courage, I think, for them to speak to us," he said.

Patton was so disgusted by Buchenwald that he ordered residents of nearby Weimar to march the few miles up the hill to see what had been going on so close nearby.

"The younger generation should get to see this," Anderson said. "It was unbelievable."

Geir Moulson contributed to this report from Berlin.