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 for the first time since its liberation by U.S. forces on April 11, 1945 — one of a group of survivors and veterans who came to mark the anniversary of the liberation.

Oster said: "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."

Around 250,000 prisoners were held at Buchenwald from its opening in July 1937 to its liberation. An estimated 56,000 people were killed.