By David Willey
BBC correspondent, Auschwitz, Poland
Sheltering from a sudden rainstorm under a white umbrella held by an aide, Pope Benedict XVI walked slowly down the line of bronze slabs by the side of the monument commemorating the 22 different nationalities of the more-than-one million victims of Nazi brutality at Auschwitz.
It was his third visit to this grim ruin in the fields. The crumbling squat barrack buildings are still punctuated by the original railway sidings where the death wagons screeched to a halt, bearing prisoners destined for the gas chambers from practically every point of Europe.
Benedict visited Auschwitz for the first time with the late Pope John Paul II in 1979. In 1983 he came again with a group of German bishops.
Then sun broke through and a rainbow appeared in the sky as he attempted to speak the unspeakable. He spoke in Italian, not in Polish.
His voice was slightly tremulous. He peppered his speech and his prayer with quotations exclusively from the Old Testament, the Holy Book common to both Christians and Jews.
"I could not fail to come here!" he exclaimed.
Twice he called himself "a son of the German people."
The first German pope in modern times was attempting to pronounce his mea culpa for Nazi war crimes.
Words failed him, he said. It was particularly difficult and troubling for a pope from Germany to speak in "this place of horror".
The Pope, who was forced as a young student in Bavaria to join the Hitler youth movement and was conscripted into, and deserted from the German army, distanced himself from "the ring of criminals who rose to power through false promises".
"Our people was used and abused as an instrument for their thirst for destruction and power. Where was God in those days?" he asked rhetorically.
Benedict the theologian gave the answer. We believe in a God of reason, not a kind of cold mathematics of the universe, he said.
"The establishment of a new centre of dialogue and prayer, a Jewish centre, and other initiatives in this place of remembrance will foster constructive thinking and resistance to evil."
Some of the 1,000 or more guests listening to the Pope's speech - who included some 200 survivors of the death camp - thought the Pope's mea culpa on behalf of the German nation was not sufficiently explicit.
Others thought he was showing great courage in tackling such a sensitive subject head on.
Of the 32 former inmates of Auschwitz who talked briefly with the Pope in the courtyard surrounding the Wall of Death, where prisoners used to be taken for summary execution, there was only a single Jewish survivor.
Former prisoners were divided over whether the Pope went far enough
His name is Henryk Mandelbaum and he is Polish.
We had no time to enquire further. The Pope's charter plane was waiting on the tarmac at Krakow airport and we had to cut and run in order not to miss the flight back to Rome.
On his arrival at the ruins of the crematoria at Birkenau the Pope had uttered a short prayer in German. It was the only moment during the entire four days that he had spoken in his native tongue out of deference to the sensitivities of his Polish hosts.
"Lord, you are the God of Peace, you are Peace: a heart that seeks conflict will not understand you. A mind that is oriented towards violence cannot comprehend you.
"Grant to all those who live in harmony that they may continue to live in peace, and grant to those who are divided the gift of reconciliation."