The 543 books, which date from the 16th and 17th century, were confiscated by German authorities in May 2012 after they were put on auction in the southern city of Munich.

The collection, which was returned to Naples on Friday is believed to have been stolen from the Girolamini libary in the southwestern Italian city between June 2011 and April 2012.

The former director of the library, Marino Massimo de Caro, was arrested in 2012 and later found guilty of the theft of the around 2,000 volumes.

"These are unique things that have changed the world," said senior public prosecutor at the Munich I Public Proscecutor's Office, Manfred Nötzel.

Some of the stolen books ended up in the hands of Marcello Dell'Utri, a close aide to former Italian Prime Minister Silvio Berlusconi and well-known bibliophile, who was jailed last year for colluding with the Sicilian Mafia, the Cosa Nostra.

Among the titles are works by Polish mathematician and astronomer Nicolaus Copernicus, English physicist and mathematician Isaac Newton, and German mathematician and astronomer Johannes Kepler.

The two most valuable books included in the collection are by Italian physicist Galileo Galilei, which alone are worth 200,000 euros.

ksb/pfd (dpa, AFP)