VENICE, Italy (AP) — Venice has always been a place of contrasts, of breathtaking beauty and devastating fragility, where history, religion, art and nature have collided over the centuries to produce an otherworldly gem of a city. But even for a place that prides itself on its culture of unusual encounters, Pope Francis’ visit Sunday stood out.

Francis traveled to the lagoon city to visit the Holy See’s pavilion at the Biennale contemporary art show and meet with the people who created it. But because the Vatican decided to mount its exhibit in Venice’s women’s prison, and invited inmates to collaborate with the artists, the whole project assumed a far more complex meaning, touching on Francis’ belief in the power of art to uplift and unite, and of the need to give hope and solidarity to society’s most marginalized.

Francis hit on both messages during his visit, which began in the courtyard of the Giudecca prison where he met with the women inmates one by one. As some of them wept, Francis urged them to use their time in prison as a chance for “moral and material rebirth.”

“Paradoxically, a stay in prison can mark the beginning of something new, through the rediscovery of the unsuspected beauty in us and in others, as symbolized by the artistic event you are hosting and the project to which you actively contribute,” Francis said.

Francis then met with Biennale artists in the prison chapel, decorated with an installation by Brazilian visual artist Sonia Gomes of objects dangling from the ceiling, meant to draw the viewer’s gaze upward. He urged the artists to embrace the Biennale’s theme this year “Strangers Everywhere,” to show solidarity with all those on the margins.

The Vatican exhibit has turned the Giudecca prison, a former convent for reformed prostitutes, into one of the must-see attractions of this year’s Biennale, even though to see it visitors must reserve in advance and go through a security check. It has become an unusual art world darling that greets visitors at the entrance with Maurizio Cattelan’s wall mural of two giant filthy feet, a work that recalls Caravaggio’s dirty feet or the feet that Francis washes each year in a Holy Thursday ritual that he routinely performs on prisoners.

The exhibit also includes a short film starring the inmates and Zoe Saldana, and prints in the prison coffee shop by onetime Catholic nun and American social activist Corita Kent.

Francis’ dizzying morning visit, which ended with Mass in St. Mark’s Square, represented an increasingly rare outing for the 87-year-old pontiff, who has been hobbled by health and mobility problems that have ruled out any foreign trips so far this year.

And Venice, with its 121 islands and 436 bridges, isn’t an easy place to negotiate. But Francis pulled it off, arriving by helicopter from Rome, crossing the Giudecca Canal in a water taxi and then arriving in St. Mark’s Square in a mini popemobile that traversed the Grand Canal via a pontoon bridge erected for the occasion.

During an encounter with young people at the iconic Santa Maria della Salute basilica, Francis acknowledged the miracle that is Venice, admiring its “enchanting beaty” and tradition as a place of East-West encounter, but warning that it is increasingly vulnerable to climate change and depopulation.

“Venice is at one with the waters upon which it sits,” Francis said. “Without the care and safeguarding of this natural environment, it might even cease to exist.”

Venice, sinking under rising sea levels and weighed down by the impact of overtourism, is in the opening days of an experiment to try to limit the sort of day trips that Francis undertook Sunday.

Venetian authorities last week launched a pilot program to charge day-trippers 5 euros ($5.35) apiece on peak travel days. The aim is to encourage them to stay longer or come at off-peak times, to cut down on crowds and make the city more livable for its dwindling number of residents.

For Venice’s Catholic patriarch, Archbishop Francesco Moraglia, the new tax program is a worthwhile experiment, a potential necessary evil to try to preserve Venice as a livable city for visitors and residents alike.

Moraglia said Francis’ visit — the first by a pope to the Biennale — was a welcome boost, especially for the women of the Giudecca prison who participated in the exhibit as tour guides and as protagonists in some of the artworks.

He acknowledged that Venice over the centuries has had a long, complicated, love-hate relationship with the papacy, despite its central importance to Christianity.

The relics of St. Mark — the top aide to St. Peter, the first pope — are held here in the basilica, which is one of the most important and spectacular in all of Christendom. Several popes have hailed from Venice — in the past century alone three pontiffs were elected after being Venice patriarchs. And Venice hosted the last conclave held outside the Vatican: the 1799-1800 vote that elected Pope Paul VII.

But for centuries before that, relations between the independent Venetian Republic and the Papal States were anything but cordial as the two sides dueled over control of the church. Popes in Rome issued interdicts against Venice that essentially excommunicated the entire territory. Venice flexed its muscles back by expelling entire religious orders, including Francis’ own Jesuits.

“It’s a history of contrasts because they were two competitors for so many centuries,” said Giovanni Maria Vian, a church historian and retired editor of the Vatican newspaper L’Osservatore Romano whose family hails from Venice. “The papacy wanted to control everything, and Venice jealously guarded its independence.”

Moraglia said that troubled history is long past and that Venice was welcoming Francis with open arms and gratitude, in keeping with its history as a bridge between cultures.

“The history of Venice, the DNA of Venice — beyond the language of beauty and culture that unifies — there’s this historic character that says that Venice has always been a place of encounter,” he said.

Francis said as much as he closed out Mass in St. Mark’s before an estimated 10,500 people.

“Venice, which has always been a place of encounter and cultural exchange, is called to be a sign of beauty available to all,” Francis said. “Starting with the least, a sign of fraternity and care for our common home.”

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Winfield reported from Rome. Associated Press writer Colleen Barry contributed.