An important document has cast new light on the role of the wartime Pope
By Edward Stourton,
BBC News, Rome
The Convent of the Quattro Coronati - the Four Crowned Martyrs - is one of those half-hidden Roman secrets that even regular visitors to the city may never discover.
Tucked away on a hillside near the Colosseum, it is a warren of buildings, some of them originating in the 4th Century. Because it is still used by an enclosed order of Augustinian nuns you can only visit the church and - if you ring a small bell - the ancient and wonderfully intimate cloister.
A document has come to light here of great significance. It is an order from the Pope during World War II, Pius XII, instructing the nuns to shelter Jewish refugees.
"The Holy Father feels in himself all the sufferings of the moment," he tells them.
"Unfortunately with the Germans' entry into Rome, which happened in the month of September, a ruthless war against the Jews has begun, whom they wish to exterminate by means of atrocities prompted by the blackest barbarities."
It goes on: "The Holy Father wants to save his children - also the Jews", and there follows a very precise list of those who should be protected, and how.
Many of them are given pseudonyms, so the list includes a "Mr Ravenna, a rabbi", who is to be hidden in the sacristy, and a Mr Viterbo and his father, "both Jews".
The accusation that Pius did not do enough to protect the Jews of Rome or to speak out against the Holocaust has been a running sore in Jewish-Catholic relations for many years.
Rome's Regina Coeli Prison, where Jews were taken before being deported
It became even more sensitive as a result of recent progress in his "cause", the process of advancing him towards beatification and eventual canonisation as a saint.
And Pope Benedict has become so concerned about the impact on Jewish-Catholic relations that he has put the matter on hold - even though evidence of the kind that has emerged from the Quattro Coronati convent has convinced the Vatican's own experts that Pius did much more than he is given credit for.
It is a reminder that, despite a huge improvement in recent decades, there are still some very raw nerves in this relationship.
And there has been a sequence of incidents under the pontificate of Benedict XVI which has made many Jews and Catholics nervous about the direction he is taking.
Benedict has shown particular concern for Catholics who have felt left behind by the changes in the modern church. He has, for example, made it easier for people to hear Mass in the old Tridentine rite.
This ancient form of Catholic worship includes a Good Friday prayer for the conversion of the Jews, and even when Benedict rewrote the prayer it caused grave offence in some quarters.
Controversy over Williamson
And then there was the Richard Williamson affair. Bishop Williamson is a member of an ultra-traditionalist sect which broke with the Catholic Church over reforms introduced in the 1960s.
Earlier this year Benedict extended a hand of friendship to the group - but he and his officials had apparently failed to notice that Williamson is a Holocaust-denier.
A quick trawl of the internet would have revealed an interview in which he said: "I believe there were no gas chambers. I believe that the historical evidence is hugely against six million Jews having been deliberately gassed in gas chambers as a deliberate policy of Adolf Hitler."
When the interview came to light it caused consternation, and Benedict was forced to apologise - something popes do not often do.
His task on the visit to Israel is not made any easier by the long shadow cast by his predecessor.
John Paul II made a hugely successful trip to Jerusalem in 2000, and is widely admired by Jewish leaders and theologians for the steps he took to improve relations between Judaism and the Catholic Church.
Rabbi David Rosen, who chairs the International Jewish Committee on Inter-religious Consultations in Jerusalem, and who will meet Pope Benedict during this trip, says the key to John Paul's approach can be found in his friendship with Jews as a young man in Poland.
"It was an inner experience for him," he says. "He grew up in that environment. He knew Jews and Judaism.
"I think that for Benedict XVI, this knowledge is cerebral rather than from the gut and it's a very positive cerebral attitude but it can't compare to that level of intimacy that was there for John Paul II."
We have found a reserve of good will towards Pope Benedict among Jewish leaders, and a real desire that this week's visit should be a success.
But it is certainly the most challenging trip outside the Vatican he has made since his election.
Catholics and Jews: War and Peace? will be broadcast on BBC Radio 4 at 13:30 on Sunday 10 May 2009