RELIGION

Vatican-sponsored conference on families spurring Pope Francis' 1st US trip

  • Workmen construct a stage ahead of the World Meeting of Families and Pope Francis's scheduled visit Monday, Sept. 21, 2015, in Philadelphia. Francis arrives in Philadelphia on Saturday. (AP Photo/Matt Rourke)

    Workmen construct a stage ahead of the World Meeting of Families and Pope Francis's scheduled visit Monday, Sept. 21, 2015, in Philadelphia. Francis arrives in Philadelphia on Saturday. (AP Photo/Matt Rourke)  (The Associated Press)

  • Pedestrians walk along the Benjamin Franklin Parkway next to barricades and port-a-potties ahead of the World Meeting of Families and Pope Francis's scheduled visit, Monday, Sept. 21, 2015, in Philadelphia. Francis arrives in Philadelphia on Saturday. (AP Photo/Matt Rourke)

    Pedestrians walk along the Benjamin Franklin Parkway next to barricades and port-a-potties ahead of the World Meeting of Families and Pope Francis's scheduled visit, Monday, Sept. 21, 2015, in Philadelphia. Francis arrives in Philadelphia on Saturday. (AP Photo/Matt Rourke)  (The Associated Press)

  • A pedestrian walks past portable toilets staged ahead the World Meeting of Families and Pope Francis's scheduled visit, Tuesday, Sept. 22, 2015, in Philadelphia. Pope Francis will attend the World Meeting's closing concert, the Festival of Families, on Saturday and celebrate Mass on Sunday. Both events are being held on the city's Benjamin Franklin Parkway. Francis will parade down the parkway's outer lanes before both events. (AP Photo/Matt Rourke)

    A pedestrian walks past portable toilets staged ahead the World Meeting of Families and Pope Francis's scheduled visit, Tuesday, Sept. 22, 2015, in Philadelphia. Pope Francis will attend the World Meeting's closing concert, the Festival of Families, on Saturday and celebrate Mass on Sunday. Both events are being held on the city's Benjamin Franklin Parkway. Francis will parade down the parkway's outer lanes before both events. (AP Photo/Matt Rourke)  (The Associated Press)

Pope Francis' six-day, three-city tour of the U.S. this week evolved from a pledge he made last fall to attend the World Meeting of Families in Philadelphia.

Stops in Washington and New York were added after Francis put the triennial, Vatican-sponsored conference on his agenda. It opens Tuesday.

Organizers describe the conference blending prayer, religious instruction and faith-themed lectures, as the world's largest gathering of Catholic families.

With more than 18,000 people signed up, this year's will be the most attended of the eight World Meetings.

Pope St. John Paul II conceived the event in 1992 to explore family bonds and the role of families in society. The first one was held two years later.

Francis arrives in Philadelphia Saturday. His packed schedule includes the World Meeting's closing concert and an outdoor Mass.