ROME It is Wednesday, May 13, 1981. On a sunbathed St. Peter's Square in Rome, a young-looking John Paul II is standing in his open vehicle, waving at the adoring congregation. He is clad in white, a broad smile on his face.

As the clock strikes 17:17, a hand holding a gun suddenly emerges from the crowd. Barely visible between two bespectacled faithful, the hand pulls the trigger and shoots, from point-blank range.

The man in white collapses, clutching his abdomen. He is helped by men in black.

Across the square, a feeling of bewilderment rapidly replaces the joy of before.

The dramatic images of the Pope being attacked are as enduring as those of U.s. President John F. Kennedy's assassination in 1963 and both incidents are key events of the 20th century.

Shortly after his serious injury, experts warned that although the Pope would probably recover physically, the attack would leave a permanent scar on his soul.

Indeed, despite a difficult operation at Rome's Gemelli Hospital that saw the removal of about 60 centimeters of his intestines, the Pope was soon fully fit again.

Today, as his 81st birthday approaches and the effects of Parkinson's disease begin to wear him down, the Pope continues to fly around the world, influencing the course of religious history.

This week, for example, he traveled to Syria and Greece, where he became the first Pope to visit a Muslim mosque and the first to apologize to the Greek Orthodox Church for the past sins of the Roman Catholic Church.

Despite the Pope looking exhausted at times, Vatican officials are already busy planning papal trips to the Ukraine and Armenia.

Some are suggesting that the Pope's enduring determination may have something to do with the fact that he once came so close to death.

"The Pope has a powerful physique, like that of a swimmer, but without the help of God he would not be able to remain so active," said Gianfranco Fineschi, an orthopaedic surgeon who has been treating the pontiff since 1981.

The Pope himself is convinced that divine intervention spared his life.

"Why didn't you die? I am certain I aimed well, that the bullet was lethal... Why didn't you die? What are they saying in Fatima?," the man who pulled the trigger was quoted as telling the Pope when visited in prison, in 1983.

Indeed, both the Pope and his assailant are shrouded in one of the biggest mysteries of the Roman Catholic Church: The so-called "third secret of Fatima."

Last year, during the Pope's visit to Portugal, the Vatican finally revealed that what for long had been thought to be an apocalyptic prediction about the end of the world was in fact a vision of the pontiff's assassination.

The message was delivered to three shepherd children in Fatima by the Virgin Mary on May 13, 1917.

"And we saw in an immense light that is God... A bishop dressed in white..." the message said. "He was killed by a group of soldiers who fired bullets and arrows at him," it added.

Vatican officials said the message was a clear reference to what would happen exactly 64 years later.

During one of his first appearances in court Mehemet Ali Agca, the Turkish terrorist who pulled the trigger in St. Peter's Square, shocked the audience by screaming blasphemous remarks about being Jesus Christ reincarnated.

His remark that the attempted murder of the Pope was connected to the third secret of Fatima was met with sniggers and perplexity.

To this date, no one knows whether Agca had any prior knowledge of the Fatima secret and why he tried to kill the Pope. Suspicions that other accomplices were present that day in St. Peter's have never been seriously investigated.

Several conspiracy theories have been put forward, but despite three investigations and two trials, the motives behind Agca's action remain obscure.

One of the most hotly pursued leads involved an alleged Soviet- inspired plot enacted by Bulgaria's secret services. After being elected Pope in 1978 Karol Wojtyla had said he would do his best to oppose communism. Three Bulgarians and three Turks were arrested but later released owing to a lack of evidence.

Other conspiracy theories, involving the CIA, the left-wing Red Brigades and former Italian prime minister Bettino Craxi never received much credence.

Antonio Marino, a magistrate who spent 15 years on the case, believes not even Agca knows the name of those behind the attack.

Last year, Agca was pardoned by Italy and was extradited to Turkey, where he is currently serving a prison sentence for the murder of a journalist. "There is only one defeat in this story: Truth," Marino remarked, according to DPA, at the time.