A crowd estimated at more than one million thronged St. Peter’s Square and the surrounding area today to watch two 20th century Catholic giants, Pope John Paul and Pope John XXIII, declared saints.

Pope Francis presided over the massive canonization ceremony, joined by his predecessor, the retired 87-year-old Benedict XVI, leading the Italian press to dub the day the “Festival of Four Popes.”

Both were historic firsts. Two popes have never before been declared saints in the same ceremony, and two living popes have never before been on hand for the event.

The canonization was the largest public gathering in Rome since the funeral of John Paul II in April 2005. In his remarks during the Mass, Pope Francis praised the two new saints.

“These were two men of courage, filled with the boldness of the Holy Spirit, and they bore witness before the Church and the world to God’s goodness and mercy,” Francis said.

Pope John XXIII, known in his day as “Good Pope John,” is remembered above all for convening the Second Vatican Council (1962-65), which launched the Catholic Church on a course of reform.

Francis today described Pope John as a “pastor” and a “servant leader,” calling him “the pope of openness to the Holy Spirit.”

John Paul II, the most traveled pope in history and the third longest-serving pontiff of all time, left behind an enormous legacy, including his role in the collapse of Communism and his outreach to both other Christians and the followers of other faiths.

Francis described John Paul as the “pope of the family,” referring to the special concern the Polish pontiff had for young people and family life. Among other things, John Paul II founded World Youth Day, a gathering staged every two or three years that routinely draws crowds in excess of a million people, becoming the Olympic Games of the Catholic Church.

The family is also a point of emphasis for Francis, who will convene a global summit of bishops in October devoted to issues related to the family.

Today is “Divine Mercy Sunday,” an observance placed on the Church’s calendar by Pope John Paul II intended to foster devotion to the mercy of Christ. Francis, who has made mercy a cornerstone of his own papacy, prayed that the two new pope-saints will help Catholics “to enter ever more deeply into the mystery of divine mercy, which always hopes and always forgives, because it always loves.”

As part of the canonization ceremony, a Vatican official asked three times that Francis name his two predecessors as saints. Francis then read a Latin formula officially “declaring and defining” that the two men have been enrolled as saints and can now be venerated by Catholics all around the world.

As part of the canonization rite, relics of each of the new saints were presented to the pope. In the case of John Paul II the relic was a vial of the late pontiff’s blood, while for John XXIII it was a piece of skin removed at the time of his beatification, the final stage before sainthood, in 2000.

Catholic teaching holds that a canonization is among the rare occasions when a pope utilizes his infallible authority, definitively asserting that the new saints are in Heaven.

The global resonance of today’s ceremony was reflected in the VIP turnout. Dignitaries on hand included twenty four heads of state and ten heads of government, with official delegations from 122 nations.

The United States was represented by a three-member delegation led by John Podesta, a former White House Chief of Staff in the Clinton administration and now a special advisor to President Barack Obama.

Italian authorities fielded some 13,000 security personnel, while the Vatican said the Mass itself involved more than 130 cardinals, 1,000 bishops and 6,000 priests from around the world. Italian media outlets quoted Roman officials as saying that more than 5,000 buses carrying pilgrims arrived in the city in the days before the event.

John XXIII and John Paul II join the subset of popes who have become saints, a total of 80 out of 268 pontiffs recognized by Catholic tradition, though just seven others have been canonized in the last 1,000 years.