Pope Francis, leader of the Roman Catholic Church, proclaimed two of his predecessors -- John XXIII and John Paul II -- as saints at a ceremony Sunday in St. Peter's Square.
Officials say as many as one million people crowded St. Peter's and the nearby streets of Rome for the elevation-to-sainthood ceremony.
Francis read the formal proclamation at the canonization Mass also attended by emeritus Pope Benedict XVI. It is the first time two former popes have been elevated to sainthood at the same time.
Relics of the two new saints were brought to the altar during the ceremony -- John Paul's blood used in his 2011 beatification, and a small piece of John's skin taken after his body was exhumed for his 2000 beatification. Relics are used to help the faithful venerate.
Churches throughout Rome were open Saturday night, filled with pilgrims from around the world who came to witness the canonization of the two 20th century popes.
The newly canonized popes are widely seen as representing contrasting factions of the Roman Catholic Church.
John, an Italian also known as the "Good Pope" because of his friendly and open personality, died before the Second Vatican Council ended its work in 1965, but his initiative set off one of the greatest upheavals in church teaching in modern times.
The Council ended the use of Latin at Mass, brought in the use of modern music, and opened the way for challenges to Vatican authority, which alienated some traditionalists.
John Paul continued some of the reforms but tightened central control, condemned theological renegades and preached a stricter line on social issues.
Groups representing victims of sexual abuse by Catholic priests say he did not do enough to root out a scandal that emerged towards the end of his pontificate and which has hung over the church ever since.
Both canonizations have involved some intervention with the normally strict rules governing the declaration of a saint. Francis ruled that only one miracle was needed to declare John a saint, while Benedict waived a rule that normally requires a five-year waiting period before the preliminaries to sainthood can even begin in order to speed up John Paul's canonization.
Some information for this report provided by AP, AFP and Reuters.