Pope Benedict XVI took his campaign to invigorate Catholics' faith to the birthplace of St. Francis Sunday, holding up the medieval playboy who became a simple friar as a model for his peaceful ways, his love for nature and his preaching of tolerance.

The pope journeyed to this Umbrian hill town, with its steep and stoney streets, to mark the 800th anniversary of the conversion of Francis of Assisi in his mid-20s from being, as Benedict put it, "the king of partying" as the son of a cloth merchant, to a deeply reflective man who embraced lepers, stripped away worldly wealth and won admirers for his gentleness and simplicity.

"Yes, my dear brothers and sisters, to convert oneself to love is to pass from bitterness to sweetness, from sadness to true joy," said Benedict during his homily at Mass in a courtyard below the 13th century St. Francis Basilica, where the saint is entombed.

Benedict praised Francis as a man ahead of his time, for his "search for peace, protection of nature, promotion of dialogue."

Like his predecessor, John Paul II, Benedict has been concerned about flagging faith among the faithful, especially in affluent societies. The anniversary of the conversion of Francis, who went to the extreme in overhauling his spiritual life, provided a suitable occasion to press the campaign to encourage faithful to better live out their faith.

"To speak of conversion means to go to the heart of the Christian message and together to the roots of human existence," Benedict said.

Millions of pilgrims and tourists come to Assisi every year to admire the medieval artwork in the basilica, including its ceiling painted by Cimabue and followers of Giotto, but also to soak up the mystical atmosphere of the town, where monks walk in sandals even in bitter winter and the voices of cloistered nuns often float through the alleys.

Some of the nuns, followers of St. Clare, another of Assisi's saints, hugged Benedict when he stopped at their pink-and-white stone basilica.

The pope moved through the streets standing in a closed-top popemobile whose windows were rolled down halfway. Earlier this month, the Vatican had a security scare when a man at the pope's public audience in St. Peter's Square tried to jump in the back of a popemobile and was wrestled to the ground by security forces. That was a different vehicle, which completely open on top and on the sides.

Benedict flew by helicopter to the outskirts of Assisi where he was greeted by Italian Premier Romano Prodi.

Benedict, 80, had a heavy schedule for his 11-hour visit in the muggy air of the Umbrian town, including several speeches, moments of private prayer before St. Francis' tomb in the lower reaches of the basilica and an early evening encounter with young people.

The late Pope John Paul II made six pilgrimages here during his papacy, including to pray for peace a few months after the Sept. 11 terrorism attacks.

Although Benedict's visit to Assisi was organized by the local bishop's office, logistics were mainly in the hands of the Franciscan friars. In 2005, Benedict curbed the independence of the friars running the one of Italy's major tourist destinations, decreeing that they must seek permission for their activities from the bishop.

The outgoing bishop had complained that he had virtually no power over the "autonomous enclaves" of the basilica, its adjoining convent and a nearby church.

The Franciscans here regularly host international peace conferences, and have welcomed controversial leaders, including, on the eve of the Iraq war, the then Iraqi deputy premier, Tariq Aziz, a Christian who had conferred with John Paul about the approaching conflict.