Ten suspects were in court on Tuesday for tampering with money from the Vatican.
The suspects, including a cardinal and four other associates, are charged with fraud, extortion, embezzlement and corruption.
It is the Vatican's first corruption case in modern history.
Central to this is a real estate deal in London.
In 2014, the Vatican invested many millions of euros in a building in Chelsea, an expensive neighborhood in the British capital.
After a few years it turned out that the investment had suffered a significant loss.
The Holy See wanted to get rid of it.
But that was not so easy.
The money was invested in a real estate fund of an Italian businessman in London.
The Vatican thus thought it owned the property.
But that wasn't the case.
A partner of the Italian businessman said that the Vatican would only become owner if 15 million euros were paid for it.
The Vatican disagreed and considered turning it into a lawsuit.
However, it feared that this would take a long time and that the judge might rule in favor of the business partner.
The amount of 15 million euros has therefore been paid anyway.
According to the prosecutors, the business partner is guilty of extortion.
The owner of the fund is also among the suspects.
Money for nun hostage went to luxury hotelshotel
In other ways too, money from the Vatican has been spent on dubious causes.
For example, a security adviser is on trial who received more than 0.5 million euros, including to free a nun held hostage in Colombia.
Instead, she spent the money on luxury products from the likes of Louis Vuitton and Prada and on luxury hotels.
The money was donated by the only cardinal on trial: Giovanni Angelo Becciu, who held a very prominent position within the Vatican.
He also donated a hundred thousand to a charity organization in Sardinia run by his brother.
He also allegedly asked a subordinate to lie to prosecutors.
The cardinal has since been removed from office.
It is not entirely clear how much Pope Francis knew about the malpractice.
Some suspects allege they acted with the Pope's knowledge.
The prosecutors also state that he approved some transactions himself, possibly without knowing all the ins and outs.
At the same time, it was Francis himself who decided to start the trial against the ten suspects.
The case is also still on Wednesday, after which a months-long suspension will probably follow. The suspects deny breaking the law.