They comprise 120 fonds of archival documents split into 20,000 units that number millions of individual pages that could keep historians busy for many years.
The documents are the Vatican archives from the era of Pope Pius XII through the Second World War. The release of the documents has long been demanded by historians and Jewish groups to ascertain the full truth about the pope's real place in history.
The Catholic Church has always argued that Pius XII helped rescue several thousand Jews by having them hidden in religious institutions in Rome during the Nazi occupation. It also believes the Pope's refusal to verbally attack the Nazis avoided reprisals against Catholics in Europe.
But Pius XII, a moral voice likely to have been heeded by German Catholics, is vilified by many historians for never having explicitly condemned the extermination of the Jews by the Nazi regime.
The member of the Roman nobility is also criticised for having remained silent when on October 16, 1943, over a thousand Roman Jews were rounded up in their ghetto not far from the Vatican.
Following the roundup, some Jews were hidden in Catholic institutions, but critics point out that no written document exists to prove that Pius XII was responsible.
Many historians conclude that while this pope may have disapproved of Hitler's anti-Semitism, he was also the product of traditional anti-Jewish Catholic teaching until the Second Vatican Council from 1962 to 1965, which positively transformed Catholic-Jewish relations.
Thus, the Jews were not the priority of this Pope, who was instead concerned about the fate of Catholics and fiercely opposed to communism, they argue.
But with the archives being opened on Monday, new information could come to light.
None of the pope's post-war papers have previously been released but in response to swirling controversy almost immediately after his death in 1958, four Jesuit priests capped 16 years of hard work by publishing 11 volumes of archival documents in 1981.
A commission of both Jewish and Catholic historians, established in 1999, decided that still more access was needed to find out the full story.
While the archives covering the Second World War have already been widely published by the Vatican, the researchers will now have direct access to an even greater number of documents – including some of the most sensitive ones.