He met them in the Basilica of St. John Lateran before meeting the faithful of Rome.
He also called for promoting a culture of adoption so that there are no abandoned children.
Arch. Wilton Gregory (71) served as president of the United States Conference of Catholic Bishops between 2001 to 2004.
It is the 20th anniversary of John Paul II's visit to Romania in 1999, which was his first trip to an Orthodox country.
