An erotic pagan fresco commissioned by one of the naughtiest popes in history has been restored and returned to the public after decades in the dark .

The fresco, in a long-closed papal apartment inside famed Rome monument Castel Sant'Angelo, illustrates the classic fable of Love and Psyche - a beautiful girl visited by a mysterious winged lover, punished by the gods when she lights a candle to see his face .

The myth - which has a happy ending - was used by the Roman philosopher Apuleius as an allegory of the soul seeking divine love. The wall painting shows Love lying in full-frontal glory while the naked Psyche leans over him, her gleaming thighs and buttocks lovingly rendered .

It was commissioned by Pope Paul III (1534-1549), a member of the powerful Farnese family who lived a wild life and sired four children before and after a marriage he renounced to become pope .

Painted in 1545-1546 by Florentine maestro Perin del Vaga, the fresco was damaged over the centuries by decay and clumsy restoration efforts - the last in the 1960s .

"This restoration is part of an important project which we have been working on for months," said Rome art expert Fiora Bellini at Thursday's reopening of the room .

"The idea is to set up a separate guided tour of the Farnese apartments, recognising their stylistic autonomy from the rest of the monument" .

Bellini said she was now hoping to get funds to restore a second, adjacent apartment used by the former Alessandro Farnese .

Like the Love and Pysche Room, the Perseus Room is called after the splendid fresco on its roof .

"The aim is to make the circuit formed by the two rooms shine out with its former splendor" .

Chief restorer Rossano Pizzinelli said: "We tried to recover the lost balance between the original painting and the successive interventions" .

"The project highlighted the quality of Perin's school, truly perfect in its mastery of all fresco techniques". There are twelve apartments in the former papal fortress on the Tiber - built on the tomb of philosopher-emperor Hadrian - but they have been closed to visitors for years .