They shuffled forward in the snow and slush, men in their 80s and 90s, their faces fixed with determination to reach the infamous camp gate once again, this time as free men.

But as Mordechai Ronan got close to the entrance of Auschwitz, his composure cracked and he began weeping. "I'm a victor! I'm a victor because I'm here!" Ronan, 85, shouted over and over between spasms of tears. He was here before in 1944 as a frightened 11-year-old who had somehow escaped the Nazi selection process that consigned most children to the gas chamber. He shouted, "Horrible place! But I am alive! We are alive!"

He was the first to reach the gate; behind him were around twenty other survivors of the most notorious death camp of the Nazi regime, all there to mark the 70th anniversary of the camp’s liberation by the Soviets on Jan. 27, 1945, to be formally commemorated Tuesday. Several of them recalled the moment they first arrived, standing before the notorious camp doctor Joseph Mengele and watching his thumb signal left or right. Right meant imminent death in the gas chamber. Left meant survival, for a few weeks at least, and forced labor.

"Somebody told me, 'Nobody ever gets out of here alive,' so the fact that I've made it I consider an accomplishment to say the least."

Let our news meet your inbox. The news and stories that matters, delivered weekday mornings. This site is protected by recaptcha

Marcel Tuchman was 21 when he stood in front of Mengele, moments after watching his uncle and two nephews sent to the gas chamber. A flick of the thumb sent Tuchman the other way, to survival. "I was told straightaway, ‘the smoke that's going up, that's what you will be,’” Tuchman, now 91,a doctor from New York, recalled Monday. “The smell of burning flesh was permeating the whole area. And I knew what it was."

The men’s sense of disbelief that they made it out alive is understandable. More than a million Jews were murdered in Auschwitz; ten thousand a day when it was operating at its peak in 1944. In eight weeks that year, more than 300,000 Hungarian Jews were send to the gas chambers, some within an hour of arriving.

Jack Rosenthal was deported from Hungary and remembers a line, long faded, near the gate at Auschwitz. "If you went beyond this point, you would be shot,” said Rosenthal, 87. “Somebody told me, 'Nobody ever gets out of here alive,' so the fact that I've made it I consider an accomplishment to say the least."

In the shadow of the Auschwitz gate, the American survivors gathered to sing a hymn of praise to God, the Kaddish, and to mourn the family and friends they had lost in the camp. Such an act 70 years ago would have meant instant death. Their voices rang out in the bitter cold like a song of defiance, and of victory over their torturers.

Many of them walked through the gate, marked “Arbeit Macht Frei” ('Work makes you free”) believing this was the end of the road for them.

Auschwitz survivors prepare for a group photograph during a gathering marking the 70th anniversary of the camp's liberation in Krakow, Poland, on Monday. Piotr Malecki / Panos Pictures / for NBC News

Survivor Harry Korman said that it all looked exactly the same as when he left it. "Even the wires on the fences that so many men threw themselves against to be electrocuted deliberately,” Korman said. “I was here naked and with wooden shoes. I've got tears in my eyes now."

Some stood silently, lost in their memories. Marcel Tuchman said: "I think of those whose voices have been silenced ... we have to tell their story.”

On Tuesday, for the 70th anniversary ceremony, they will sit at the end of the railway line, just a hundred yards from the gas chambers and ovens that annihilated a million and more in a frenzy of industrialized killing. They will hear speeches and they will pray again. But today, they shouted their defiance and their warning: "Never, never let this happen again."