The mass, which Francis will precede with a tour around St. Peter's Square, will begin at 9:30 a.m., Italy's ANSA news agency reported.
The celebration, which the Rev. Federico Lombardi said will be marked by "simplicity," will begin at St. Peter's tomb, where the Piscatory ring, a ring cast in gold for each pope, and the Pallium woolen robe of the papacy will handed off to Francis, the Vatican spokesman said.
Then, the Gospels will be sung in Greek and communion will be given by the deacons of the church square and 500 other priests, but not by the pope.
Delegations from 132 countries and international organizations are expected to attend the mass. U.S. Vice President Joe Biden, who is Catholic, will be representing his country as President Barack Obama is in Israel.
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