As many as 1 million pilgrims and other visitors are expected at the Vatican on Sunday for the canonization of two of the most influential popes of the 20th Century, John Paul II and John XXIII.
Pope Francis will be assisted during the sainthood ceremony by retired Pope Benedict XVI, the first time two living pontiffs will help canonize a pair of their predecessors.
Giant screens have been erected in piazzas throughout the city for those unable to get into St. Peter's Square for the Mass, which is expected to begin at 10 a.m. local time (1 a.m. PST) and last about two hours.
John XXIII, who is said to be a favorite of Francis, was born Angelo Giuseppe Roncalli to a poor rural family in Italy. Although he served as pontiff less than five years, from 1958 until his death in 1963, he is credited with modernizing the Roman Catholic Church.
He convened the historic Second Vatican Council, which instituted such reforms as Masses in the vernacular instead of Latin.
Born Karol Wojtya in Wadowice, Poland, John Paul II would become the first non-Italian pope in more than 400 years when he was elected in 1978. He was beloved by Catholics around the world for his warm, personal style and fierce opposition to Soviet communism.
John Paul II served as pontiff for almost 27 years, surviving an assassination attempt in St. Peter's Square in 1981. He later forgave his attacker.