He appeared stronger than in recent days, as he addressed thousands in the town famous for its ancient ruins left over from the eruption of Mount Vesuvius in 79 A.D., reports CBS News' Sabina Castelfranco.
Only last month, the 83-year-old pontiff, stooped and slowed by Parkinson's disease and other health problems, struggled through a four-day pilgrimage to Slovakia, and a cardinal last week said John Paul was approaching his dying days.
John Paul's speech was often halting, and he slurred his words as he read opening prayers for peace. He skipped portions of his speech, but he looked alert and happy to be back in Pompeii after 24 years.
Before heading back to the Vatican by helicopter after his three-hour visit, he even seemed buoyed. He sounded stronger as he asked the faithful in improvised remarks to "pray for me in this sanctuary, today and always."
Some 30,000 pilgrims, many of them standing under palm trees in a packed square in front of the shrine here dedicated to the rosary, applauded in encouragement, especially when he paused in his speech.
Shouts of "Long live the pope!" resounded from the crowd.
"I wanted this pilgrimage of mine to carry the sense of an appeal for peace," John Paul told the faithful after praying the rosary with them.
The pontiff, who vigorously opposed the war in Iraq, lamented that the new millennium "is already lashed by the winds of war and stained with blood in so many regions of the world."
Some in the crowd wore costumes from their native lands, including a few with Mexican sombreros.
After an hour's flight from Vatican City by Italian air force helicopter, John Paul arrived in a space in ancient Pompeii's ruins which was a gymnasium in Roman times.
These ruins, the pope said, are witness of a great culture. Today, just as in the times of ancient Pompeii, it is necessary to announce Christ to a society which is moving away from Christian values.
Along the route to the sanctuary, John Paul, sitting in an upholstered chair in the white, open-topped "popemobile," waved constantly to joyous pilgrims.
Several dire assessments of his health recently by top prelates heightened concern over whether his physical frailty allows him to continue in the papacy.
An intestinal ailment forced him to skip a public audience at the Vatican on Sept. 24.
The Vatican devised a mini-lift to allow John Paul to board helicopters, which he used to fly regularly in his frequent trips. Parkinson's plus knee problems make it impossible for John Paul to climb stairs to board.
For several months now, John Paul has rarely been seen walking or even standing in public. He navigates the vast spaces of St. Peter's Square and Basilica in a kind of throne-like chair on wheels guided by aides.
"I love the pope. He's the most holy man on Earth," said Ella McLoughlin, a pilgrim from Worcester, Mass. "I think God still wants to use him. That's why he's still alive."
A local churchman, Monsignor Domenico Sorrentino, told the pope, "May the Lord keep you for a long time as a prophet and witness of peace."
The century-old shrine is very dear to the pope, who considers the rosary a powerful form of prayer.
The sanctuary draws some 4 million faithful each year to Pompeii, now a sleepy town flanking the sprawling ruins.