The 84-year-old pontiff died Saturday evening at the Vatican after suffering heart and kidney failure following two hospitalizations in as many months.
The Vatican released the pontiff's official death certificate Sunday, saying he died of septic shock and an irreversible cardio-circulatory collapse and listing the ailments he suffered from, including officially acknowledging that he had Parkinson's disease, reported the Associated Press.
Streams of pilgrims converged on Rome and some 130,000 worshippers gathered at St. Peter's Square to hear John Paul's words read at a Requiem Mass. The pope had prepared the text for the mass before his death.
"It is love which converts hearts and gives peace," an archbishop read as many listeners wept.
In the Apostolic Palace's Clementine Hall, two Swiss guards stood on either side of the pope's body, which was placed in front of a fireplace adorned with the Vatican's coat of arms, a crucifix standing to one side and an ornate candle burning on the other.
Prelates and Italian Premier Silvio Berlusconi were among those who stood in line to pay their respects. Vatican officials also in attendance included close papal aide Cardinal Joseph Ratzinger, American Cardinal Edmund Szoka, Polish nuns, the pontiff's personal doctor, and his longtime personal secretary, Archbishop Stanislaw Dziwisz, according to the AP.
The body will be moved from the Apostolic Palace on Monday afternoon to St. Peter's Basilica for a public viewing.
John Paul's death set in motion a series of rituals that end one papacy and start another, which could last up to a month.
In the past, rituals had involved tapping the pope's forehead three times with a silver hammer, but the last version of the official Vatican document outlining the procedures does not mention the silver hammer, saying only that the camerlengo "must officially obtain the pope's death," the AP reported.
Within 15 to 20 days, the 117 cardinals from around the world charged with electing the next pope will go behind closed doors in the Vatican's Sistine Chapel. When they make their decision, white smoke will pour from the chapel's chimney.
There is no favorite candidate to succeed John Paul. The former Archbishop Karol Wojtyla of Wadowice, Poland was the first non-Italian to become pope in 450 years.
Meanwhile, Rome was preparing for up to 2 million pilgrims to descend on the city, working to provide extra trains, fresh water and thousands of beds, according to Reuters.
Rome authorities planned to erect giant screens across the city for pilgrims to follow celebrations.