The Vatican is opening up archives documenting its relations with Nazi Germany amid accusations that the then Pope failed to speak out against the Holocaust.
The archive includes the office records of Cardinal Eugenio Pacelli, the Vatican's ambassador to Berlin from 1922 to 1929, who went on to be pope during the war.
As Pope Pius XII, who led the Roman Catholic Church from 1939 to 1958, he has long been accused by Jewish groups of turning a blind eye as many Jews were marched off to concentration camps.
The archive is being opened on Saturday - but only to scholars by special appointment.
According to archive custodian Sergio Pagano, much of the material in the documents has already been published.
"More interesting material is due to be made available to historians in three years time," he told Italy's Corriere della Sera newspaper.
He added that delays in opening the archive were due to a "shortage of personnel, and not a desire to hide anything."
The Vatican has admitted, however, that files dating from 1931 to 1934 were "nearly completely destroyed or dispersed" during the bombing of Berlin and by a fire.
In 2001, Catholic and Jewish scholars investigating the Vatican's relations with Nazi Germany suspended their research in protest at the huge amount of material kept secret.
Jewish groups at the time also called on the Vatican to delay the beatification of Pius XII.
'Criticism'
The Vatican has long countered criticism by saying Pope Pius XII did not speak out for fear of worsening the situation for Catholics as well as Jews in occupied territories during the war.
The Catholic Church has been criticised for not revealing the extent of its possible involvement or complicity in the Holocaust, in which six million Jews and hundreds of thousands of other ethnic minorities, gypsies and homosexuals were killed.
In March 2000, Pope John Paul II asked for forgiveness for wrongs inflicted by the Catholic Church on Jews, minorities and women.
However he angered Jewish groups for stopping short of mentioning specifically the Holocaust or the possible role of Pope Pius XII.