President Andrzej Duda laid flowers at rail tracks in Oświęcim in southern Poland, where the Germans ran the largest of their concentration and death camps during World War II.
It was there that on June 14, 1940, the Germans brought 728 Poles to the Auschwitz camp, which was still under construction at the time, from a prison in the southern city of Tarnów.
It was the start of the one the darkest chapters in modern history.
Duda said the earth at the site was "soaked in blood, and has the ashes from burned human bodies scattered over it."
He added that it was "a land that cries out for remembrance, a land that also cries out for us to never forget, so that something like that never happens (again)”.
The Auschwitz-Birkenau Nazi death camp operated in German-occupied southern Poland between May 1940 and January 1945.
More than 1.1 million people, mostly European Jews, as well as Poles, Roma, Soviet POWs and people of many other nationalities, perished at the camp before it was liberated by Soviet soldiers on January 27, 1945.