ONE of the great heroes of the 20th century was Auschwitz prisoner No. 4859, who volunteered to be there.

Witold Pilecki, an officer in the Polish resistance to the Nazi regime, deliberately let himself be captured by the Germans in 1940 so that he could gather information about Hitler’s concentration camps. Inside Auschwitz, he set up resistance cells — even as he almost died of starvation, torture and disease.

Then Pilecki helped build a radio transmitter, and, in 1942, he broadcast to the outside world accounts of atrocities inside Auschwitz — as the Nazis frantically searched the camp looking for the transmitter. He worked to expose the Nazi gas chambers, brutal sexual experiments and savage camp punishments, in hopes that the world would act.

Finally, in April 1943, he escaped from Auschwitz, bullets flying after him, and wrote an eyewitness report laying out the horror of the extermination camps. He then campaigned unsuccessfully for an attack on Auschwitz.

Eventually, he was brutally tortured and executed — not by the Nazis, but after the war, in 1947, by the Communists. They then suppressed the story of Pilecki’s heroism for decades (a book about his work, “The Auschwitz Volunteer,” was published in 2012).

I was thinking of Pilecki last week on the 70th anniversary of the liberation of the Auschwitz-Birkenau death camps. I had relatives killed in Auschwitz (they were Poles spying on the Nazis for the resistance), and these camps are emblems of the Holocaust and symbols of the human capacity for evil.

In the coming months, the world will also commemorate the 100th anniversary of the start of the Armenian genocide — which, despite the outrage of Turkish officials at the term, was, of course, a genocide. There, too, I feel a connection because my ancestors were Armenian.

Then, in the summer, we’ll observe the 70th anniversary of the end of World War II — an occasion for recalling Japanese atrocities in China, Korea, the Philippines and elsewhere. All this is likely to fuel more debates focused on the past. Should we honor Armenian genocide victims with a special day? Should Japan apologize for enslaving “comfort women”?

But, to me, the lesson of history is that the best way to honor past victims of atrocities is to stand up to slaughter today....