A rarely seen painting by Italian master Caravaggio, part of a private collection, is being displayed to the public for the first time in an exhibition in Rome.

"The Portrait of Maffeo Barberini" features the future Pope Urban VIII, who hailed from the noble Roman Barberini family and was a friend of Caravaggio's patron.

Born in 1568, wealthy humanist Barberini was elected in 1623 to the throne of Saint Peter, which he held until he died in 1644.

The painting was authenticated in 1963 by the art critic Roberto Longhi, a great specialist in the work of the 16th-century artist.

Longhi says the undocumented painting was part of the Barberini family collection for centuries before passing into private hands in the 1930s.

"Caravaggio – The Portrait Unveiled" will run from Nov. 23 to Feb. 23 at the Barberini Palace, the family's historic home, which now houses part of the National Galleries of Ancient Art.

The Palace also permanently houses four other works by Caravaggio, whose real name was Michelangelo Merisi, including "Judith Beheading Holofernes," "Narcissus," "Saint John the Baptist" and "Saint Francis in Meditation."

Maffeo Barberini was "not only a mighty man of power but also a great and refined intellectual," and Caravaggio's portrait of him is "of very great value," gallery director Thomas Clement Salomon told Agence France-Presse - (AFP).

"It has never been lent to an exhibition; it has never been seen in a museum, so it is an absolute preview," he said.

"The portraits painted by Caravaggio can be counted on the fingers of one hand, so showing one to the public and experts is exceptional."

The Maffeo Barberini portrait, with its sparsely colored decor, "plays on light and shadow," Caravaggio's signature style, art historian and curator Paola Nicita told AFP.

"The heart of the painting lies in the hands: the left hand clutching a letter ... and the right hand emerging from the painting, entering our space," she said.

"It is a painting that expresses itself through gestures," she added.

"This marvelous gesture of the outstretched right hand is very reminiscent of the gesture of Christ in 'The Calling of Saint Matthew'," she said, referring to one of Caravaggio's most famous works, which hangs in the St Louis of the French church in Rome.