The pontiff walked alone and in silence around the former concentration camp
Pope Francis has visited the former Auschwitz death camp to mourn the more than one million mostly Jewish victims who died at the hands of the Nazis.
After walking through the notorious "Arbeit Macht Frei" (Work Sets You Free) gate at the camp, Pope Francis paid his respects in silence with a quiet prayer and meditation.
He is the third pontiff to make the pilgrimage.
His Polish hosts took him to Birkenau, the main extermination site, driving him along the two miles of track laid in 1944 for trains of prisoners to be transported right to the gas chambers and crematoria.
Pope Francis also met Holocaust survivors in front of the death wall where the Nazis summarily shot thousands of inmates.
He prayed in the cell where Polish priest and saint Maximilian Kolbe died after taking the place of a condemned man - the visit falls on the 75th anniversary of the day Kolbe was sentenced to death.
The pontiff, who has been trying to forge ever-closer ties between the Catholic Church and members of the Jewish faith since his election in 2013, met 12 survivors, including a 101-year-old woman, at the site which is now a memorial and museum.
He also met some 25 Christians who risked their lives during the war to help hide and protect Jews in Poland - a group recognised by Israel's Yad Vashem as "Righteous Among the Nations".
Writing in the guest book at the death camp, he said: "Lord, have pity on your people. Lord, forgive so much cruelty."
Poland's Chief Rabbi Michael Schudrich, who was saying prayers with the Pope, said: "Often people go to Auschwitz... and they are silent (about the horrors) for the rest of their lives.
"Instead, once we leave Birkenau we must spend the rest of our lives screaming, yelling and fighting all kinds of injustices."
More than 100,000 non-Jewish Poles, Roma, Soviet prisoners of war, homosexuals and anti-Nazi partisans also died at the camp in the then occupied Poland which was liberated by the Russians in 1945.