Humanity will soon be without first-hand witnesses of the depths to which it can sink. Survivors at the memorial knew that

They came to bear witness one last time. Exactly 75 years after the Red Army’s liberation of Auschwitz, those who had seen humanity’s descent into hell returned to speak of it while they still could – and with a new, double urgency. They testified like people running out of time, aware that their own mortality is pressing in on them – and alarmed that the world needs to hear their message now more than ever.

There were fewer than 200 of them at Monday’s international ceremony, confirmation that their ranks are becoming thinner and more frail with the passage of time. Feted as honoured guests in the place where once they were reviled inmates, even together they filled just a few rows. They were at the front of a vast marquee, large enough to house the iconic “gate of death” through which those men and women – almost all mere boys and girls at the time – had passed when it was not theatrically lit to make a spectacular backdrop for television, but when it had the power to terrify.