On Monday, survivors of the Nazi Holocaust met for what may be their last big reunion.
Some 1,000 survivors and World War Two vets gathered on the 20th anniversary of the U.S. Holocaust Museum in Washington, D.C.
They have first hand memories of one of the greatest human tragedies of all times.
"Do not enter this place without hope nor without fear of what humanity has done to itself by failing, for such a long time, to save those who were threatened by the common enemy," said Elie Weisel, former director of the Simon Wiesenthal Center.
Under the direction of Germany's Adolph Hitler, Nazis killed 6 million Jews and 5 million others who were also considered inferior because of race, beliefs or handicaps.
Hitler's henchmen systematically killed these innocents, most notoriously in extermination camps using gas chambers.
But miraculously, hundreds of thousands survived and have been able to recount their stories for decades.
Now, 68 years after World War Two ended, many survivors have died. And activists wonder what will happen when the eyewitnesses no longer remain, when so-called "perceived history" becomes "received history."
At the museum's 20th anniversary gathering, speakers urged participants to keep history alive.
"As direct memories fade away, let the records, the pictures, the stories, never die," former President Bill Clinton said.
The museum launched a new fund-raising campaign to promote awareness, fight growing anti-Semitism and counter those who deny the Holocaust.