They are old. And they are the last who can testify to us about what it was like -- the darkness, the unspeakable darkness. For others, the smell of burning bodies, human smoke from the crematoriums, lingers forever in memory.
Today's commemoration was noticeably smaller than those in previous years. Only a few world leaders came and the U.S. sent the Treasury secretary.
However, as the terror attacks in Paris and other recent anti-Semitic incidents in Europe and elsewhere have demonstrated, Jews are once again being targeted just because they are Jews.
"For a time, we thought that the hatred of Jews had finally been eradicated," Ronald Lauder, the president of the World Jewish Congress, told those assembled at today's ceremonies. "But slowly the demonization of Jews started to come back.
"Once again," Lauder said. "young Jewish boys are afraid to wear yarmulkes on the streets of Paris and Budapest and London. Once again, Jewish businesses are targeted. And once again, Jewish families are fleeing Europe."
Added Roman Kent, an 85-year-old Holocaust survivor, fighting back tears, "We do not want our past to be our children's future."
The Associated Press contributed to this report.