Vatican officials toured Philadelphia on Tuesday ahead of a major Roman Catholic gathering that the city's archbishop believes will include an appearance by the pope.

Archbishop Charles Chaput said he's "personally convinced" the pontiff is coming to the World Meeting of Families in September 2015. But he stressed that nothing is certain until an official announcement from the Holy See, which won't come for several months.

"There's every indication he is coming," Chaput said.

His remarks came after local organizers unveiled the meeting's theme: "Love is our mission: The family fully alive." The weeklong conference, which aims to strengthen family bonds among people of all faiths, is being overseen by the Pontifical Council for the Family.

Council president Archbishop Vincenzo Paglia arrived in Philadelphia on Monday, about two months after a local delegation traveled to see him in Rome. On Tuesday morning, he saw the Liberty Bell and Independence Hall accompanied by Mayor Michael Nutter and Pennsylvania Gov. Tom Corbett.

Taking inspiration from the site where the Constitution was written, Paglia described his goal for the international symposium: "I would like to write the importance of the family for the contemporary world."

Paglia wouldn't speculate on which other cities Francis might visit during a U.S. tour. Paglia plans to visit the United Nations in New York on Thursday for the International Day of Families.

On his way into Tuesday's news conference at the Independence Visitors Center, Paglia stopped to chat with some tourists who turned out to be members of a choir from Waldorf College in Forest City, Iowa.

After the mayor told choir director Adam Luebke why Paglia was in town, the singers began serenading the archbishop with the Latin hymn "Ubi Caritas."

"It was completely impromptu," Luebke said afterward, adding that the group had only planned to see Independence Hall and get a cheesesteak.

Later, when Paglia was asked what he would tell Francis about his trip, the archbishop said he'd convey the welcome that he received. And, he added, "Surely I will give to the pope a little bell from Philadelphia."